# Rough idle and poor acceleration '02 1.8T Jetta



## Full Metal Foil (Nov 26, 2008)

Friday my car decided to give me problems. While I was driving home from work my acceleration went to complete crap. When I would press on the accelerator, the engine would bog down and fight with me. I got it home and it sounds horrible while idling. I took it into Auto Zone to have them test the code. (code is at home) The code stated that the fuel injector or fuel injector wiring may be bad and to check it. The odd thing is, once the guy cleared the code it ran perfect for about 5 miles before bogging down again. Makes me think that something other than the fuel injector is failing if it will run like a top for 5 miles before starting up again. What could it be? Any help is much appreciated.
I bought this used '02 1.8T Jetta about 5 months ago. I have been having the "usual" part failures that come with this car. So far I have changed the crappy water pump out with one that does not have plastic turd impellers, put in a new timing belt, thermostat, and fixed the broken oil dipstick casing. Now this problem has emerged. 










_Modified by Full Metal Foil at 12:58 PM 6-1-2009_


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## Full Metal Foil (Nov 26, 2008)

*Re: Rough idle and poor acceleration '02 1.8T Jetta (Full Metal Foil)*

Changed the spark plugs lastnight, the old ones were gapped at .042. I corrected the problem and made the new plugs .032. Still runs very rough. I put some Fuel Injector cleaner in the fuel system, will see how that works. Is there a way to tell if the coils are bad? The first one looked brand new, but the other three look like they have seen better days. 
Engine still is running rough at idle and when accelerating.


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## MyFirstGTI1.8T (Jan 9, 2008)

*Re: Rough idle and poor acceleration '02 1.8T Jetta (Full Metal Foil)*

Did you have a CEL? Blinking CEL is the best indicator of a failed coil.


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## AutomaticJoy (Sep 27, 2007)

*Re: Rough idle and poor acceleration '02 1.8T Jetta (MyFirstGTI1.8T)*

clean the throttle body?
I know when my car was idling rough, we had a VW tech friend scan it with the dealer computer. A code came up and he said "odds are, your throttle body needs to be cleaned"
The butter fly had some crap gunked around the gap making it idle bad.
We cleaned it later that day, and Its ran fine ever since. Worth a try


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## Full Metal Foil (Nov 26, 2008)

*Re: Rough idle and poor acceleration '02 1.8T Jetta (MyFirstGTI1.8T)*


_Quote, originally posted by *MyFirstGTI1.8T* »_Did you have a CEL? Blinking CEL is the best indicator of a failed coil. 

The CEL was blinking. I'm going out at lunch and picking up the new "R" type coils for the car. When I replaced the spark plugs I did notice the coils looked pretty worn out.


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## Full Metal Foil (Nov 26, 2008)

*Re: Rough idle and poor acceleration '02 1.8T Jetta (AutomaticJoy)*


_Quote, originally posted by *AutomaticJoy* »_clean the throttle body?
I know when my car was idling rough, we had a VW tech friend scan it with the dealer computer. A code came up and he said "odds are, your throttle body needs to be cleaned"
The butter fly had some crap gunked around the gap making it idle bad.
We cleaned it later that day, and Its ran fine ever since. Worth a try










I think I will also clean the throttle body and MAF while I'm at it, just to get everything done at once.
Should I place a new wiring harness in for the coils as well while I'm at it? 
Thanks for the advice so far guys. Love this forum.


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## Full Metal Foil (Nov 26, 2008)

*Re: Rough idle and poor acceleration '02 1.8T Jetta (Full Metal Foil)*

Update...
I changed out all of the Ignition Coils today. It ran better than ever for about 30 minutes. After a while it kicked back into it's rough idling and accelerating like hell. This thing is weird. I checked the coil wiring and it looks very new. I think the stealership put new ones in about 4 months ago. I made sure the coils were secure and pressed the wiring into the coils till I heard them click into place. It's almost like something is jarring loose once in a while and then connecting back up later on. I started it up a while ago after the rough accelerating and it ran fine, but then started acting up 10 minutes later. It's driving me crazy!








Here were the error codes before changing the coils out.
_______________________________________
P0300: Random Cylinder Misfire Detected
Explanation: Lean Air/Fuel Ratio
Probable causes:
- Ignition system misfire condition
- Fuel injector fault
- Engine mechanical condition
_______________________________________
P0301: Cylinder 1 Misfire Condition
Explanation: Vacuum leak on engine
Probable causes:
- Ignition system fault
- Fuel injector fault
- Engine mechanical condition
_______________________________________
P0303: Cylinder 3 Misfire Condition
Explanation: Vacuum leak on engine
Probable causes:
- Ignition system fault
- Fuel injector fault
- Engine mechanical condition
_______________________________________
P0203: Injector Circuit Open - Cylinder 3
Explanation: Open or short circuit condition
Probable causes:
- Poor electrical connection
- Faulty fuel injector
_______________________________________
P1780: Engine Intervention Readable - No Communication between ECM and TCM
Explanation: Open or short circuit condition
Probable causes:
- Poor electrical connection
- Failed TCM
_______________________________________
Something is screwy...


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## mini911 (Feb 22, 2003)

*Re: Rough idle and poor acceleration '02 1.8T Jetta (Full Metal Foil)*

i'm troubleshooting a different problem - mine is idling perfectly fine just starts cutting out when i really get on it.
i unplugged the MAF today to see if it made a difference and the idle went to ish. try disconnecting your MAF and see if the problem gets any worse. if nothing happens, you may need a new one.....among other things.
g/l


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## Full Metal Foil (Nov 26, 2008)

*Re: Rough idle and poor acceleration '02 1.8T Jetta (mini911)*


_Quote, originally posted by *mini911* »_i'm troubleshooting a different problem - mine is idling perfectly fine just starts cutting out when i really get on it.
i unplugged the MAF today to see if it made a difference and the idle went to ish. try disconnecting your MAF and see if the problem gets any worse. if nothing happens, you may need a new one.....among other things.
g/l

I unplugged it the other day and the car went crazy. Idled like crap and when I plugged it back in and started it up, it would jump everytime it shifted until I shut the car off and back on again. It's crazy.


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## Full Metal Foil (Nov 26, 2008)

Any ideas from the codes of what might be going on?


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## JettaRed (Aug 14, 2000)

*Re: (Full Metal Foil)*

Do you have an automatic? (That's what the TCM is for.)
Sometimes when the throttlebody starts to fail (and they do fail, though rarely), you will get the symptoms you describe.


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## Full Metal Foil (Nov 26, 2008)

*Re: (JettaRed)*


_Quote, originally posted by *JettaRed* »_Do you have an automatic? (That's what the TCM is for.)
Sometimes when the throttlebody starts to fail (and they do fail, though rarely), you will get the symptoms you describe.

Yeah, it is an automatic. It has Tiptronic shifting as well. I need to check that throttlebody out. I haven't given it a good cleaning yet. 
Do you recommend trying that?


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## Full Metal Foil (Nov 26, 2008)

Is there a good site to buy some decently priced fuel injectors?


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## JettaRed (Aug 14, 2000)

*Re: (Full Metal Foil)*

Ususally it's the electronics that fail in the throttlebody, so cleaning wont work. I recently got injectors from http://www.024motorsport.com for a good price.


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## Full Metal Foil (Nov 26, 2008)

*Re: (JettaRed)*


_Quote, originally posted by *JettaRed* »_Ususally it's the electronics that fail in the throttlebody, so cleaning wont work. I recently got injectors from http://www.024motorsport.com for a good price.

Well I'm hoping it's not the whole TB. Ugh... That's a pricey fix. I will check it out tonight.


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## AutomaticJoy (Sep 27, 2007)

*Re: (Full Metal Foil)*


_Quote, originally posted by *Full Metal Foil* »_
Well I'm hoping it's not the whole TB. Ugh... That's a pricey fix. I will check it out tonight.

just clean it. im telling ya. its worth it to spend the 20mins before you go dropping money on all this other stuff. Mine is an automatic too. I dropped a good chunk of chage buying new spark plugs, new hitachi coil packs, heat sheild and MAF cleaner. The entire time, after talking to our VW tech friend...it was the stupid crap cloggin the throttle flange.


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## Full Metal Foil (Nov 26, 2008)

*Re: (AutomaticJoy)*


_Quote, originally posted by *AutomaticJoy* »_
just clean it. im telling ya. its worth it to spend the 20mins before you go dropping money on all this other stuff. Mine is an automatic too. I dropped a good chunk of chage buying new spark plugs, new hitachi coil packs, heat sheild and MAF cleaner. The entire time, after talking to our VW tech friend...it was the stupid crap cloggin the throttle flange.









It's my first priority once I get home. Thanks again for the help. As strange as it may sound, I'm hoping that damn TB is dirty and causing the problem. An easy fix would be great. I will post the results later tonight. 


_Modified by Full Metal Foil at 9:04 AM 6-3-2009_


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## AutomaticJoy (Sep 27, 2007)

*Re: (Full Metal Foil)*


_Quote, originally posted by *Full Metal Foil* »_
It's my first priority once I get home. Thanks again for the help. As strange as it may sound, I'm hoping that damn TB is dirty and causing the problem. An easy fix would be great. I will post the results later tonight. 

Ill cross my fingers for you for you! I just wished I knew about mine before i spent all the money, but I guess new coil packs were going to be needed eventually. Hopefully what you need isn't gonna damper your funds any


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## Full Metal Foil (Nov 26, 2008)

*Re: (AutomaticJoy)*


_Quote, originally posted by *AutomaticJoy* »_
Ill cross my fingers for you for you! I just wished I knew about mine before i spent all the money, but I guess new coil packs were going to be needed eventually. Hopefully what you need isn't gonna damper your funds any

Thanks Auto! I'm going to guess the TB is gunked up. The guy who owned the car before me did not do any of his own maintenance. He took it into the shop once in a while, but I'm doubting that the TB was ever touched. I bought it at 85k miles. 
The car has A LOT more pick up with these new coil packs and (correctly gapped) Autolite plugs (When it decides to run smooth). The only thing that keeps me wondering is why it decides to run perfect one second, and like complete crap when I start it up the next time. It's messing with me.


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## AutomaticJoy (Sep 27, 2007)

*Re: (Full Metal Foil)*


_Quote, originally posted by *Full Metal Foil* »_

The car has A LOT more pick up with these new coil packs and (correctly gapped) Autolite plugs (When it decides to run smooth). The only thing that keeps me wondering is why it decides to run perfect one second, and like complete crap when I start it up the next time. It's messing with me. 

Well...it IS a Volkswagen. hah. Is this talk about spark plugs and ignition... Im due for some new sparkplugs. Still waiting on my EJ Y and T hoses to get here.


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## Full Metal Foil (Nov 26, 2008)

*Re: (AutomaticJoy)*


_Quote, originally posted by *AutomaticJoy* »_
Well...it IS a Volkswagen. hah. Is this talk about spark plugs and ignition... Im due for some new sparkplugs. Still waiting on my EJ Y and T hoses to get here.

I just changed out my Y hose. It had a nice sized crack running through it. Good times!







Hopefully you get them soon.


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## Full Metal Foil (Nov 26, 2008)

*Failed again...*

Well tonight I cleaned out the Throttle Body very well. It did have a lot of carbon built up on it. I changed out my fuel filter because I'm not sure when the last guy did it. I took my MAF off and cleaned it out with CCC MAF Cleaner. I put the key in, turned it one click and let it sit for about 15 minutes. I turned it on and it is still idling like crazy... I suppose I should change these fuel injectors out. This thing is driving me nuts. haha
Anyone know of a good deal on a VAG-COM? I'm thinking about purchasing one. Now would be a good time...


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## Full Metal Foil (Nov 26, 2008)

Would a VAG-COM be able to clear codes and program the computer back to factory settings?


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## AutomaticJoy (Sep 27, 2007)

*Re: (Full Metal Foil)*

http://www.ross-tech.com/vag-com/vag-com-faq.html 
dunno if its in there or not


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## Full Metal Foil (Nov 26, 2008)

*Re: (AutomaticJoy)*


_Quote, originally posted by *AutomaticJoy* »_ http://www.ross-tech.com/vag-com/vag-com-faq.html 
dunno if its in there or not

Actually I found the needed info. Thanks! The $249 KII USB setup should work for my car right? (2002 Jetta 1.8T) I have a laptop to use it on. Here is the link to the one I'm looking to buy: CLICK HERE


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## Full Metal Foil (Nov 26, 2008)

I just find it very odd that once Auto Zone clears my codes for me, the car runs perfect for about 15-30 minutes... If it was a faulty fuel injector, wouldn't it run like crap even after clearing the codes?


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## CFLdub (Sep 7, 2008)

*Re: (AutomaticJoy)*

Do you have a multimeter? Before you drop money on injectors, clean the contacts on the harness and the injectors themselves with electronic cleaner, also make sure your getting proper fuel pressure. You can also try cleaning your Throttle position sensor. Its the plastic part attached to the throttle body, those clips pop off and snap back in. Use electronics cleaner to clean the TPS and make sure you align your throttle body once you have put it back on the intake. http://****************.com/smile/emthup.gif


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## Full Metal Foil (Nov 26, 2008)

*Re: (CFLdub)*


_Quote, originally posted by *CFLdub* »_Do you have a multimeter? Before you drop money on injectors, clean the contacts on the harness and the injectors themselves with electronic cleaner, also make sure your getting proper fuel pressure. You can also try cleaning your Throttle position sensor. Its the plastic part attached to the throttle body, those clips pop off and snap back in. Use electronics cleaner to clean the TPS and make sure you align your throttle body once you have put it back on the intake. http://****************.com/smile/emthup.gif 

I can pick up a multimeter. They aren't too expensive. I will do that tonight. I will also check out the other areas that you listed. Thanks for the advice CFLdub.








Also, just to be clear... To align the TB I should just have to let the car sit for 15 minutes with the key turned to ACC? 
_Modified by Full Metal Foil at 7:02 AM 6-4-2009_


_Modified by Full Metal Foil at 7:48 AM 6-4-2009_


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## Full Metal Foil (Nov 26, 2008)

*Re: (CFLdub)*

Check this out! I was cleaning the TPS out and look at the prong on the third cylinder... hmmmm... 








I fixed the problem and positioned each prong into place. I will see what happens once I get done with the alignment.


_Modified by Full Metal Foil at 5:55 PM 6-4-2009_


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## Full Metal Foil (Nov 26, 2008)

*Re: (CFLdub)*

The wheel in this photo fell out when I was cleaning the TPS. I'm worried that I maybe I didn't put it back in the EXACT way it was before. Does it need to be lined up a certain way?
-I also cleaned the wiring connectors on the fuel injectors, and on the harness.








After going through the alignment process the car runs a bit better... I have more power, but it still fights me sometimes while accelerating. I only ran it for 10 minutes or so. It idles better, but still kinda rough. Ugh...


_Modified by Full Metal Foil at 5:06 AM 6-5-2009_


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## Full Metal Foil (Nov 26, 2008)

The car is back to acting like a jerk this morning. Rough idling and loss of power while accelerating. Should I just break down and take it to the local shop?


_Modified by Full Metal Foil at 9:02 AM 6-5-2009_


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## Full Metal Foil (Nov 26, 2008)

I let it sit and idle for 5 minutes or so and the idling leveled out and went back to its smooth self. I drove it for about 10 minutes with no problems. When I got off work I turned it on again and it's back to the rough idling and lack of acceleration. What would cause that? I thought maybe leaving it sit like that allowed the computer to readjust everything back to factory settings and fixed itself up, but I'm not sure why it went back to the rough idling after letting it sit. Any ideas?


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## Full Metal Foil (Nov 26, 2008)

Anybody else had this problem?


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## Full Metal Foil (Nov 26, 2008)

Figured out that it was, in fact, the fuel injector on cylinder 3. It was electrically shorted somehow. Thanks for all of the help everyone. Appreciate it.






















She runs like a beast now!










_Modified by Full Metal Foil at 9:12 PM 6-11-2009_


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## Chuckizgod (Nov 26, 2007)

mine did the same thing but it ended up being a bad coil. I replaced all of them, runs like a champ.


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## JettaRed (Aug 14, 2000)

*Re: (Full Metal Foil)*


_Quote, originally posted by *Full Metal Foil* »_Figured out that it was, in fact, the fuel injector on cylinder 3. It was electrically shorted somehow. Thanks for all of the help everyone. Appreciate it.






















She runs like a beast now!











There should have been a DTC for that. Did you ever scan your car?


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## Full Metal Foil (Nov 26, 2008)

*Re: (JettaRed)*

These were the codes i got from AutoZone.
P0300: Random Cylinder Misfire Detected
Explanation: Lean Air/Fuel Ratio
_______________________________________
Probable causes:
- Ignition system misfire condition
- Fuel injector fault
- Engine mechanical condition
_______________________________________
P0301: Cylinder 1 Misfire Condition
Explanation: Vacuum leak on engine
Probable causes:
- Ignition system fault
- Fuel injector fault
- Engine mechanical condition
_______________________________________
P0303: Cylinder 3 Misfire Condition
Explanation: Vacuum leak on engine
Probable causes:
- Ignition system fault
- Fuel injector fault
- Engine mechanical condition
_______________________________________
P0203: Injector Circuit Open - Cylinder 3
Explanation: Open or short circuit condition
Probable causes:
- Poor electrical connection
- Faulty fuel injector
_______________________________________
P1780: Engine Intervention Readable - No Communication between ECM and TCM
Explanation: Open or short circuit condition
Probable causes:
- Poor electrical connection
- Failed TCM
_______________________________________
I mean, it did state that one of the many causes could have been the Fuel Injector. I just wanted to start searching the cheap fixes first. I did tune her up a bit in the process. 
I am having new problems already though. My new code of the week is as follows:
/////
Error Code: P0420
Definition: Catalyst System efficiency below threshold bank 1
Explanation: Faulty Catalytic Converter
Probable Causes:
1. Rich Air/Fuel Ratio
2. Air Leak near rear H02S
3. Faulty fuel control H02S
/////
Oh joy!


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## Flurrymail (Apr 18, 2007)

*Re: Rough idle and poor acceleration '02 1.8T Jetta (Full Metal Foil)*

Hello. I bought my GTI almost two years ago, and while the max power it produces still comes close to 95% of the OEM-as-new power, the idle has ALWAYS been a pain in the butt. It's neither jerky nor random (like something really bad is happening), just constantly ROUGH from morning starting to stopping from highway cruisin' and everything in between.
When bought, I almost immediately changed the coil pack to an "E" revision by Hitachi. Same roughness (they never fail, though).
Also, I replaced the air filter with a K&N that gets cleaned constantly. Always buy the high octane fuel and occasionally drop a bottle of octane booster to boot.
A few months ago I personally cleaned the MAF sensor, temp sensor and "degunked" the electronic throttle body to a mirror luster.








Last month I cleaned the valve gear of all hard crud and sludge, cleaned the oil pan and pickup screen.















A week ago I replaced the fuel filter. I'm still having a rough idle.








I'm considering doing a professional fuel injectors cleaning next week. Can somebody shed me some light in this matter (the idle a/o the pro injection cleaning job)?
Please help! Thank you all in advance just for reading this lengthy post.











_Modified by Flurrymail at 7:10 PM 6-28-2009_


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## Chuckizgod (Nov 26, 2007)

when I replaced all the ignition coils last monday 2 days later my cylinder 1 coil fried and started misfiring again. I had the wiring harnesses replaced and rewired since I found the wires were grounding out to the valve cover. engine runs a lot more powerful and smoother now, and at idle you can't even tell the motor is on unless you look at the serpentine belt turning.


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## That_Crayon_Smell (Jul 12, 2009)

*Re: (Chuckizgod)*

Im in the same rough idle boat here too. My 1.8T has a rough idle on cold starts. Sometimes it trips the CEL. But the idle is always corrected after about 30sec or so. This is when "something" whines down and the idle smooths out...Kinda weird.
Im assuming my injectors, plugs and coils are fine because of the smooth idle afterwards. Im thinking it's something to do with whatever sensor is active on cold starts... MAF? Throttle components? No idea...
So far i've re-gapped the copper plugs to .032". Coils and wires appear fine. Im always using Shell v-power fuel. And synthetic oil 5w-40. I've got about 175K km's on it. (Just got it used about 10K ago)
Are there diagrams here online that show us noobs how to clean a throttle body, TPS, MAF or PCV replacement???
Btw, thanks Full Metal Foil for your updates. Interesting things to look out for!


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