# MkIV 2.0L Hesitation & Rough Idle



## nweurosport (Jan 16, 2003)

Having some difficulties with my MkIV Jetta. I'm getting a little bit of a rough idle, a definite stumble every 3 seconds or so. The engine vibrates noticably to the touch/sight if you pop the hood. The car also hesitates heavily under 3k rpms. Once you hit 3k it seems to pick up just fine.
This hesitation seems to disappear at WOT which makes me suspect the TPS. Does anyone have the TPS test procedure handy? I don't have a MkIV Bentley sitting around.
There is also a strong possibility one or more of the plug wires got damaged during a plug service. There is probably some misfiring from the wires.
Any other complications with the MkIV 2.0L's that people have come across routinely? Do the late model 2.0L's get their TB's all buggered up with carbon like the earlier ones? I'll go investigate mine tommorow morning.
Thanks for your help. Planning on doing a good amount of routine maintainance since it just hit 65k. Looking at timing belt, serpentine belt, plugs, wires, PCV, fuel filter, trans fluid. 
I'm trying to sell this thing...








-Andy


----------



## king_hil (Mar 4, 2003)

*Re: MkIV 2.0L Hesitation & Rough Idle (nweurosport)*









bump for a fellow washingtonian...land of the crazy people who drink coffee like it was water


----------



## QuackDuck (Feb 21, 2003)

*Re: MkIV 2.0L Hesitation & Rough Idle (nweurosport)*

Is your check engine light on? Are your spark plug gaps correct? Is your air filter clean? When was the last time you replaced your fuel filter? Is your Air flow meter healthy? That's all I can think of. If you have a misfire, the check engine light should be on. 
I had crapy performance issues when my stock NGK plugs were nearing their end. Try using Bosch Platinum 2 plugs. NGKs are not the best choice for this engine IMO.


----------



## nweurosport (Jan 16, 2003)

*Re: MkIV 2.0L Hesitation & Rough Idle (QuackDuck)*

The check engine light came on a while ago noting the MAF. The MAF was replaced but the computer was not reset. The code went away on it's own after a week. Are there compensation numbers that might still be floating around in the computer that I didn't wipe out?
The plugs are Platinum+4's which I think are questionable. The air filter is K&N and recently bathed. The fuel filter is questionable. Those things are all on my list. 
Thanks for the suggestion.
-Andy


----------



## Cyclopath (Sep 1, 2002)

*Re: MkIV 2.0L Hesitation & Rough Idle (nweurosport)*

Was the MAF changed before or after the filter got its bath? May have too much oil on the filter and it coated the sensor.


----------



## jettaray76 (Jan 15, 2003)

*Re: MkIV 2.0L Hesitation & Rough Idle (nweurosport)*

man i would check your fuel filter and it could even be your cat.. how many miles?? i would do plugs wires and fuel filter and see where that gets ya. You might want to take it to a muffler shop and have them check your cat ....


----------



## QuackDuck (Feb 21, 2003)

*Re: MkIV 2.0L Hesitation & Rough Idle (nweurosport)*


_Quote, originally posted by *nweurosport* »_
The check engine light came on a while ago noting the MAF. The MAF was replaced but the computer was not reset. The code went away on it's own after a week. Are there compensation numbers that might still be floating around in the computer that I didn't wipe out?
The plugs are Platinum+4's which I think are questionable. The air filter is K&N and recently bathed. The fuel filter is questionable. Those things are all on my list. 
Thanks for the suggestion.
-Andy


More than likely the problem is caused by Bosch Platinum +4 spark plugs. Run search on Vortex and Usenet. Many engines that are switched to the +4 plugs exhibit the problems that you describe. Buy a set of cheapo Auto Lite plugs for testing ($1 each) and see if that will make the problem go away. +4 plugs are highly problematic in many engines. I too wanted to try those +4 plugs but after reading about the poop that people experienced with them I decided to go with Platinum 2, and I couldn't be happier. Many 2.0 owners opt for ordinary copper core plugs because they give a "hotter spark." The only real advantage of platinum plugs is their longevity. I use platinums because changing the plugs on the 2.0 is too painful to do very often. 


_Modified by QuackDuck at 12:57 PM 6-6-2003_


----------



## 2kjettaguy (Dec 24, 2000)

*Re: MkIV 2.0L Hesitation & Rough Idle (QuackDuck)*

oxygen sensor #1 could be bad. Did you ever have the recall performed?


----------



## nweurosport (Jan 16, 2003)

*Re: MkIV 2.0L Hesitation & Rough Idle (2kjettaguy)*

I had the recall done aboue 20k miles ago. What exactly did it address? It was a software update for the heating circuit wasn't it? Could the O2 sensor be faulty without throwing a code?
-Andy


----------



## 2kjettaguy (Dec 24, 2000)

*Re: MkIV 2.0L Hesitation & Rough Idle (nweurosport)*

I am not sure what the ecu upgrade invloved. I just got a new sensor because I have neuspeed's supercharger chip flashed in. From what i heard the sensors were very slow to react. 
Have you thought about the MAF? Those things are such little bastards when they go out. So much of the time any poor engine behavior can be blamed on the MAF


----------



## thefish77 (Jan 22, 2002)

*Re: MkIV 2.0L Hesitation & Rough Idle (nweurosport)*

Damnit! I just bought some new +4's and wires to do a change at 65k. I have had the same thing for awhile too, so keep the info coming. It really annoys me. Did you notice that it does it when you re-start the car hot, but no issues on warmup?


----------



## QuackDuck (Feb 21, 2003)

*Re: MkIV 2.0L Hesitation & Rough Idle (nweurosport)*


_Quote, originally posted by *nweurosport* »_
I had the recall done aboue 20k miles ago. What exactly did it address? It was a software update for the heating circuit wasn't it? Could the O2 sensor be faulty without throwing a code?
-Andy

The recall consisted of replacement of the #1 oxygen sensor and reset of ECU computer. Original oxygen sensors did not tolerate sudden teperature changes too well, and they cracked. People who started the cars in the morning and drove cold engines as if they were warm (3,000 RPM+) right away got the check engine light. 
My recall letter did not mention anything about any software changes, besides, ECU runs embedded software and I don't see how you could update firmware without replacing the chip - the actual hardware.


----------



## nweurosport (Jan 16, 2003)

*Re: MkIV 2.0L Hesitation & Rough Idle (QuackDuck)*


_Quote, originally posted by *QuackDuck* »_
The recall consisted of replacement of the #1 oxygen sensor and reset of ECU computer. Original oxygen sensors did not tolerate sudden teperature changes too well, and they cracked. People who started the cars in the morning and drove cold engines as if they were warm (3,000 RPM+) right away got the check engine light. 
My recall letter did not mention anything about any software changes, besides, ECU runs embedded software and I don't see how you could update firmware without replacing the chip - the actual hardware. 

That's interesting. I thought Motronic chips were flashable. Can anybody point me at a good source for a Motronic manual? Is there a Bentley manual specific to Motronic tuning?
-Andy


----------



## nweurosport (Jan 16, 2003)

*Re: MkIV 2.0L Hesitation & Rough Idle (thefish77)*


_Quote, originally posted by *thefish77* »_Damnit! I just bought some new +4's and wires to do a change at 65k. I have had the same thing for awhile too, so keep the info coming. It really annoys me. Did you notice that it does it when you re-start the car hot, but no issues on warmup?

Yeah, basically everywhere I look I hear bad things about the +4's. Where'd you end up getting the wires? Are they decent quality? I'm n ot ready to spring for OEM ones from the dealer, but I want a quality piece of equipment.
-Andy


----------



## thefish77 (Jan 22, 2002)

I got the OE Beru wires from Bow Wow- I'll run the +4's until they start screwing up- they were 4 bucks apiece, so i'm not out too much. Any ideas on where to have them installed? I was gonna try it, but after looking at it, i don't see how to change the plugs and wires without taking off the damn upper intake manifold!


----------



## nweurosport (Jan 16, 2003)

*Re: (thefish77)*

I'm always more than happy to help out. It's not as impossible as it appears. The plugs are actually angled perfectly to get a socket in through the manifold runners. The tricky parts is removing the plug wire boot which is where I think they got buggered up when mine were done.
-Andy


----------

