# 1.8T Cold start misfire - mechanic stumped



## rubba.chikin (Nov 8, 2013)

*1.8T Cold start misfire - mechanic stumped [UPDATE]*

Hey guys,

Fairly new GTI owner here, had it for about 3-4 months now.
Apart from a failed alternator it has run fine as a daily.

I bought it towards the end of summer and it's run well until winter started creeping in.
Started off being a little rough during cold starts, but it's progressed enough to cause the CEL to come on.
After the cold start (mech said Open Loop stage?) the idle stabilises and it runs perfectly fine until it's cold again.

My workmate also has the same vehicle albeit slightly more modified and he nudged me towards the forums here in the hope of possibly figuring out this issue.
He has a VAGCOM cable so I'm able to read the fault codes.

Originally it showed up as:
Random Intermittent Misfire
Cyl 3 Intermittent Misfire
Cyl 4 Intermittent Misfire

Watched a live misfire count on a cold start, all cylinders were missing but 3 & 4 significantly more.
Cleared the codes and drove it for a week, could feel the missing on cold starts and a few days in CEL back on.

I'm handy with tools, but not enough knowledge to jump into engines without some help/advice.
I decided to take it to a local VW Performance shop that replaced the alternator previously.

They switched coils from 3 & 4 to 1 & 2, still missing more on 3 & 4.
Swapped the plugs 3 & 4 to 1 & 2, drove it for half a week till the CEL came back on.

Codes read as:
Random Intermittent Misfire
Cyl 1 Misfire Detected
Cyl 2 Misfire Detected
Cyl 3 Misfire Detected
Cyl 4 Intermittent Misfire

Mech starting saying things about possible crack between valves so I started ****ting bricks.
Leakdown test overnight, no pressure drop. Cranked over under pressure, no drop.

I read a load of threads here about cold misfires, lots came back to the MAF and also the SAI pump. 
I tried one morning unplugging the MAF and I think ironically it started up way smoother, so I thought we nailed it.

Replaced the MAF and it seemed better, but the last 2 days cold starts were rough and today the CEL is back.
Mech said he's checked the SAI pump and the vacuum lines and he's pretty much stumped.
Said it could be a custom tune but this car has no performance mods that I know of so I highly doubt it.

Like I said earlier, when the cold start process ends the idle drops and I can still hear the SAIP and when it shuts off BAM stable idle.

Anyone offer any insight into this?
It's driving me crazy!


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## AmIdYfReAk (Nov 8, 2006)

Hows it run with the MAF unplugged?

What plug model/gap are you running?

Hows the wiring to the coil packs?

Is there any misfires under boost? Cold or warm?


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## rubba.chikin (Nov 8, 2013)

The first time with MAF unplugged it seemed to run fine apart from one little blip.
However since having MAF swapped out and issues returned I tried it unplugged yesterday and it was still missing so I do not think it has anything to do with the MAF any more.

I have no idea on the gap, not something I could tell you.

Forgot to mention in the original post the mechanic checked the coil pack harness, said there were a few suspect wires they cleaned up and re-taped but nothing obviously bad.

The misfire isn't super violent, not close to stalling or anything like that.
If I hold the revs up higher like 1.5-2k it still misses.
Originally when the mech thought it could be a minor crack in the head he asked about blipping the throttle on the cold start to see if it was water vapour in the cylinder which would evaporate quickly and the idle settle down. Tried that, giving it a quick stab it'll choke and miss worse and settles back down to missing idle until the cold start sequence is done.

As soon as the cold start cycle is finished the car runs fine, under boost is smooth normal power.
Idling at lights it seems to hang around 750 rpm, very occasionally it has a little dip down below that but nothing that seems bad.

It's really hard to troubleshoot because after you've started it and it's warm it won't miss again for several hours until it's stone cold.


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## Sycoticmynd29 (Jan 17, 2011)

When was the last time the spark plugs were changed?

You went from codes for cyl 3 & 4 misfires to codes for all 4 after moving the plugs around.

What Coolant Temp Sensor do you have? I believe this sensor plays a large role in controlling fueling until the car warms up.

Also, check for vacuum leaks, and loose connections.

Things contract when cold and expand when warm, so a rubber hose could be contracting, causing a loose connection or a leak, then when the car is warmed up, expanding to close the leak.

Just my ideas :thumbup:


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## [email protected] Performance (Sep 17, 2013)

Throw new plugs in, and gap them down to .028. Stock is .032, but the tighter gap will take the stress off of the coil packs. Might fix it.

Clean your ait sensor with denatured alcohol (it's located on the back of the intake manifold, and held in with 1 Allen bolt)

Pressure test your intake tract via one if the methods in the FAQ, and fix all vacum/boost leaks that you find.

Go through all of those steps, THEN report back.


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## rubba.chikin (Nov 8, 2013)

Sycoticmynd29 said:


> When was the last time the spark plugs were changed?
> 
> You went from codes for cyl 3 & 4 misfires to codes for all 4 after moving the plugs around.
> 
> ...


The live misfire count still seems to show more misfires on 3 & 4.
Just after several days of cold starts the cumulative results was misfire on 1,2,3 and intermittent on 4.

Not sure on the coolant temp sensor.. how do I check?
I did see that mentioned in a few of the other cold start issue threads.

I should also mention I checked with a VW Dealer and confirmed the coils were replaced in March 2010 as part of the recall.


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## warranty225cpe (Dec 3, 2008)

Plugs > coil packs > harness. Diagnosed in that order.


My money is on your harness :beer:


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## Sycoticmynd29 (Jan 17, 2011)

rubba.chikin said:


> The live misfire count still seems to show more misfires on 3 & 4.
> Just after several days of cold starts the cumulative results was misfire on 1,2,3 and intermittent on 4.
> 
> Not sure on the coolant temp sensor.. how do I check?
> ...


I'd still suggest replacing your plugs and gapping them per Jeff's advice

The CTS is located in the plastic flange on the DS side of the head.

Black top CTS is outdated, green top CTS is more recent. As for checking if it's working correctly, I have no idea.


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## Dr. Stu (Jul 30, 2011)

Coolant temp sensor replacement youtube video

Green is Good! Black is Bad!


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## [email protected] Performance (Sep 17, 2013)

These are old cars. It's called "do a tuneup".

Coil harnesses go bad

Plugs go bad

Sensors go bad

Coil packs go bad 

Vacum/pcv lines leak

Start replacing old, worn out stuff, and the car will run properly.


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## rubba.chikin (Nov 8, 2013)

Ok thanks for the input guys.

I think my workmate and I can handle throwing some new plugs in and probably the CTS, even coils if it came down to that.
What's the effective lifespan for coil packs anyway? Having them replaced in 2010 doesn't seem that long ago.

Can someone tell me the specific extra gear that runs for the cold start procedure? The idle consistently stabilises immediately once the revs drop and the SAIP shuts off. Obviously the SAIP is one, if it was a vacuum leak which other components should I be focusing on?


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## [email protected] Performance (Sep 17, 2013)

Make sure you gap the plugs down to .032 or even .028; as it takes the strain off the coil packs. Coil packs usually go bad from too large of a plug gap.

Also clean your ait sensor with denatured alcohol. It's located on the back of the intake mani by the throttle body. It'll cause misfires too


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## [email protected] Performance (Sep 17, 2013)

Pressure test it using the stickied procedure at the top of the forum.

If your sai pump is indeed leaking it's an easy fix. You simply drill out the rivets, silicone the two halves together, and use nuts/bolts to clamp it back together.

Pressure testing is key though. I guarantee that you'll find small vacum/boost leaks everywhere, and even the smallest leaks cause issues with the hypersensitive me7 ecu.


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## rubba.chikin (Nov 8, 2013)

Ok so an update.

The MAF got replaced last time it was at the mechanic so it was to be swapped back if it ended up not faulty. 
That was the case so while it was there I asked him to throw in new plugs gapped to .028.
No dice, still missing.

He had a brand new set of OEM 1.8T coils in the workshop so he threw them on, same deal still missing.
Said he's been over the lines a few times and cannot find any leaks.
No labour charge for the last lot of stuff so he's not trying to ream me there.

So...

New plugs gapped to 0.28 = cold start misfire remains
New coil packs = cold start misfire remains
CTS = green unit reading correctly on diagnostics
AIF = reading correctly on diagnostics 

Really the only thing left is the coil pack harness and to do a complete pressure test... for which I do not have or have access to air compressor other than the gas station. 

He said he could throw a chipped ECU into the car temporarily to try more comprehensive fault diagnostics, but other than that it's a hard bastard to figure out.


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## [email protected] Performance (Sep 17, 2013)

Pressure test/

We've done enough parts changing at this juncture


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## Sycoticmynd29 (Jan 17, 2011)

Can't believe I forgot about this, there was a service bulletin about cold start misfires. 
Its an issue with the ECU software.

Not sure if it applies, but its possible

Linky to the Thread

Just a link to the thread with the discussion, I didnt compare your car to whats there


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## riskyroller (Jan 16, 2003)

i had a misfire issue that drove me crazy. it turned out that i had ripped(slightly) the o rings on my injectors. ( bottom into the manifold) when i installed them. it gave me random misfires and injector open circuit codes on 2 and 4. those were the injectors with the ripped o ring. i tried replacing everything from the coil pack harness to the maf. after i replaced the o rings it hasnt missed since.


good luck


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## gigel (Sep 13, 2005)

I am pretty sure you have a vacuum leak. Since 3 and 4 show more misfires, I would say some vacuum line connected on that side of the engine. Check the pipe that goes to the brake booster. You can spray carb cleaner around and see if it changes the idle (keep in mind, that carb cleaner can catch on fire, too). Can you read fuel trim with vag com when is misfiring? You can't if it happens only in open loop but maybe it's still misfiring when in closed loop with the engine cold.


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## Slimjimmn (Apr 8, 2006)

1: check and clean the throttle body (residue buildup will cause rough idle cold as the throttle can't properly open )
2: make sure it has ngk plugs only
3: verify with vag com the sw level for he ecu. The reflash fixes cold start misfires for 1.8t

Also might want to check for exhaust leaks, specifically the turbo to mani gasket and bolts.


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## robin_bga (Jun 23, 2011)

Hi, I would also suggest checking the pressure of your fuel pump, if am not wrong, a good pump should be in between 30-40psi am not really sure but if someone has the real values, then please post the but I believe that is your culprit. 
Cheers R

Audi A3 1.8T, 
8L AUQ, 2001 
Manual transmission


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## mrbatavus (Nov 29, 2008)

Check fuel pressure , sounds like it's leaking down when it sits and it's starving for fuel when you start it up after it say for a while, could be bad fuel pump, injector, could also be carbon build up on intake valves, try running seafoam through it

How old is the fuel filter?


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## rubba.chikin (Nov 8, 2013)

Ok so a few months later now with an update.
So I kinda jumped the gun announcing it was no better.

After the mech installed gapped down plugs he said it was still missing and it wasn't perfect, I updated this thread that night... however it was good enough to not trip the CEL anymore.

I drove the car for 1 maybe 1.5 months with no CEL. 
It eventually tripped CEL for random misfires on 1 cylinder and I cleared that and it was good for maybe another ~2 weeks.
It gradually got worse and now it's missing fairly obviously and it'll trip the CEL at least every second start.


So seeing the new smaller gapped plugs made it better, but not fully fixed... is it possible the coils are slowly killing the plugs faster than they'd usually degrade?
Or the coils themselves are degrading and have gotten worse since having the plugs changed?


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## cesmith (Sep 1, 2007)

coils if you have not done them, and coil harness if you have


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## radlynx (Jan 4, 2007)

what did you replace previously? say yes or no if you replaced the following and when.
spark plugs?
ignition coils?
crankshaft position sensor?
fuel filter?
fuel injector?
camshaft position sensor?

anything that you can add would be very helpful.




rubba.chikin said:


> Ok so a few months later now with an update.
> So I kinda jumped the gun announcing it was no better.
> 
> After the mech installed gapped down plugs he said it was still missing and it wasn't perfect, I updated this thread that night... however it was good enough to not trip the CEL anymore.
> ...


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## radlynx (Jan 4, 2007)

from your post above, you have not switched the fuel injector between 1 - 2 and 3-4. it could be that your 3&4 fuel injector is dying. what's your current mileage?



radlynx said:


> what did you replace previously? say yes or no if you replaced the following and when.
> spark plugs?
> ignition coils?
> crankshaft position sensor?
> ...


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## rubba.chikin (Nov 8, 2013)

radlynx said:


> from your post above, you have not switched the fuel injector between 1 - 2 and 3-4. it could be that your 3&4 fuel injector is dying. what's your current mileage?


The shop swapped the injectors I believe.
The missing is across all cylinders, or last time I checked I had random + Cyl 2, 3 and 4.

spark plugs? YES - gapped to .028 

ignition coils? YES/NO - but the shop threw on a set of new VW OEM coils temporarily and advised the miss was still there at start
I have been told the original coils are garbage and my buddy replaced his with 2.0T coils

crankshaft position sensor? NO

fuel filter? NO

fuel injector? NO - but I believe they swapped them around and the miss didn't move/remained consistant

camshaft position sensor? NO


MAF was also swapped out with a new unit, but that didn't fix it and was changed back to the exisiting MAF


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## radlynx (Jan 4, 2007)

thanks I appreciate it. check with the shop if they really did swap out the fuel injectors. someone mentioned here that a leaking oring can also cause that. also, make sure you have the correct fuel pressure. your fuel pressure regulator might be bad since it's missing across all the cylinders. have them change the fuel filter so that if you have new one, the fuel pressure might increase and stop this random misfire. in my car, i have a fuel pressure gauge installed so if this happens to me, first thing i would check is the fuel pressure. your fuel pump might be dying too and not giving enough pressure.



rubba.chikin said:


> The shop swapped the injectors I believe.
> The missing is across all cylinders, or last time I checked I had random + Cyl 2, 3 and 4.
> 
> spark plugs? YES - gapped to .028
> ...


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## EsquireMyke (Jan 26, 2006)

Check the crankcase breather hoses under the intake manifold for broken hoses or sticking breather check valve. Here a good link of illustration. http://www.audizine.com/forum/showt...he-AWD-ATC-1-8T-Breather-Hose-Kit-10-Off!-***
But also noted there was a software update for cold start misfires, I believe it was for 2002 years, but don't take my word on that.


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## Chickenman35 (Jul 28, 2006)

> *Forgot to mention in the original post the mechanic checked the coil pack harness, said there were a few suspect wires they cleaned up and re-taped but nothing obviously bad.
> *


This statement is very suspicious. If you have a " few " suspect wires, then the harness is likely TOAST!! And once you start moving the harness around to change coils etc, you end up getting more breaks in the wire insulation. It gets very brittle over time. The ground points are also critical.

VW used a very poor insulation in these harnesses. It cannot stand up to the under hood temperatures and is a common failure point. Being a common failure point, your mechanic should have known this and been extra diligent . I have to question how well he inspected the harness ( usually the whole harness has to be unwrapped ).

Personally, there are very,very few shops in the Vancouver area that I trust with any of my cars. I can recommend Shift Auto Sport in Burnaby though. VW experts ( they Road Race them ) and know there stuff. Just out of interest. Would you mind sending me a PM of the shop you're now using. 

SAI pump also sounds suspect. Or hoses/check valves leading from it. I know your mechanic said he's already checked it...but sometimes a second opinion ( or mechanic ) is needed. Just my hunch...


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## Chickenman35 (Jul 28, 2006)

Here's an interesting question. We've had some cold, but dry weather, the last few days. Have things gotten a bit better?

When it's raining ( which it does a lot in Vancouver winters ), poor wiring insulation and connection issues get worse. It's the damp weather. When the engine gets warm, the moisture evaporates from the electrical harness and the misfires due to shorts/poor connections can go away. The problem is worse on Rainy days or days with heavy Dew. A sure sign of harness or terminal moisture sealing problems. And wrapping exposed wires with electrical tape will NOT keep out the moisture. It's a Mickey Mouse band-aid " attempt " at a fix. I won't even do it justice by calling it a " Fix ". ( Hint: I think you need a new mechanic. Just my .02c ).

Vintage British car and bike owners are very familiar with this problem. Lucas electrics are notorious for acting up in wet weather... LOL.


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## Pass18t (Oct 18, 2003)

Replace coolant temp sensor.


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## BassNotes (Mar 16, 2005)

Leaky fuel injector O-rings can be a cause of cylinder-specific vacuum leaks.


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## noelskii (May 19, 2012)

http://www.audiforums.com/forum/audi-a6-9/a6-3-0-cold-start-misfire-cyl-4-p0304-132381/

his reply:



> I did solve the problem, mine was bad valve seals leaking oil into the cylinder while the engine sat overnight.
> 
> The thing you want to do is
> Let the engine sit overnight
> ...


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## BISHILVR (Nov 17, 2011)

My vote is your cam position sensor.


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## mk21.8Tjetta (Jun 3, 2002)

Bringing this back from the dead. To the OP, did you ever figure this out? I'm having the exact same problem, misfire on cold start. When the SAI pump shuts off and the idle drops, the misfire stop immediately and the car runs fine. I have an aftermarket exhaust so I can hear it. Sounds like a Subaru lol. I've had misfire CEL's and a system lean code also.

I've done pretty much everything you have, to no avail. Hoping you had some luck.


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## mk21.8Tjetta (Jun 3, 2002)

mk21.8Tjetta said:


> Bringing this back from the dead. To the OP, did you ever figure this out? I'm having the exact same problem, misfire on cold start. When the SAI pump shuts off and the idle drops, the misfire stop immediately and the car runs fine. I have an aftermarket exhaust so I can hear it. Sounds like a Subaru lol. I've had misfire CEL's and a system lean code also.
> 
> I've done pretty much everything you have, to no avail. Hoping you had some luck.


Hello? Anyone have any ideas?


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## PeteFede (Sep 27, 2018)

Had the exact same problem. Cold start missing during high idle warm up. (In my case codes were intermittent on Cyl 2 and 4) Problem slowly worsened to missing after warm up and oil started appearing on the exterior of the valve.
Issue was the "pancake" crankcase pressure regulator valve at back of the engine. The diaphragm had failed and was leaking to atmosphere through the vent behind the diaphragm.
You can check operation of the valve by blocking off one side and sucking on the other to move the diaphragm. If it does not operate, or air comes in through the vent it is faulty.
Took me over a year to finally diagnose the problem.


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