# MAF/rough idle...HELP!



## observer (Mar 24, 2004)

I've been struggling with rough idle for a long time now. Any advice will be appreciated








Items replaced:
- MAF
- DV
- all new PCV parts
- new N80 valve
Observations:
- VAG indicates misfires on cyl2 (+- 9 per minute) at idle, none at WOT
- When aircon is on no misfires evident
- When MAF unplugged no misfires evident
- Lean at idle code on VAG
- Car is not pulling smoothly
- Actual and requested boost good
- Fuel pressure at around 110bar during load
Fixes tried
- Reset settings etc
- Cleaned MAF - no luck
- Unplugged MAF - no misfires and car goes pretty strong but not 110%
- Propane spary to test for vac leaks - none found
- Swapped coils and spark plugs - misfire still present on cyl02 
Only other item I can think of is blocked injector but why then does it idle fine with MAF unplugged?


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## bwzimmerman (Jun 16, 2007)

i am by no mean a mechanic, but if your car runs fine with it unpluged then maybe its a bad sensor.
either that, or check for boost leak. I had a simmilar problem and it was a small boost leak. A clamp broke on my FMIC and it cause a gap about the size of a quarter.. all better and car runs perfect.

or maybe a bad coil pack on cyl 2?


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## Arin (Jun 27, 2002)

*Re: MAF/rough idle...HELP! (observer)*

possibly a bad injector?
Also there is a TSB that states if everything you've done doesnt change the misfires, you may need to have your exhaust valve rocker arms replaced.


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## observer (Mar 24, 2004)

*Re: MAF/rough idle...HELP! (Arin)*

Definitely not a bad coil pack as I changed them around as well








Arin, I agree that it might be an injector but why then does it run fine with the MAF unplugged? This also sort of throws the RSB recommendation out the window or am I wrong?








Everything point to the MAF as I see it but it has already been replaced 2 time and I cleaned the current one yesterday with no luck. Will request a change again and see if it helps...maybe I just had a couple of dud MAFs but I doubt it.
I'm not a mechanic but would unplugging the MAF not hide the fact that there is a vacuum leak somewhere and that is why it idles fine with the MAF unplugged? 
As I understand it the car then relies on the oxygen sensor in the exhaust to ensure a correct A/F ratio, right?


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## Arin (Jun 27, 2002)

*Re: MAF/rough idle...HELP! (observer)*

It's strange that it's on only one cylinder. If it was any sensor causing the problem, or any leak (other than internally in the engine) I'd expect misfires on all cylinders.


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## observer (Mar 24, 2004)

*Re: MAF/rough idle...HELP! (Arin)*

I have once seen a misfire on another cylinder but that was about 30k miles ago and never again. 99.99999% of the time it is on cyl 2








When I unplug the MAF the revs does not jump between 720rpm and 760rpm that much...stays very close to requested 760rpm. Same for the A/F ratio Maybe by unplugging the MAF the ECU just add a VERY small amount of fuel (as a safety factor) at idle to mask the injector problem. All speculation of course








When the MAF is plugged in I have sort of a dip in power at arounf 4K rpm and then is comes back again. With the MAF unplugged this dip in power is gone. With MAF unplugged the car spins like mad in 1st with it unplugged no spinning of wheels. Must be the MAF.....just hope that by unplugging the MAF I'm not masking a vacuum leak


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## teeOHkay (Feb 22, 2008)

*Re: MAF/rough idle...HELP! (observer)*

i have been experiencing the same problem with my car! i have a mkv gti also with the same problem. My car seems to idle really rough then when i hit the gas from a dead stop the car seems to hesitate then it just jolts forward really hard and boosts heavily. then when i lay my foot off the gas or shift into neutral while slowing down the RPMS drop to 0 sometime it will spike back up sometimes the car just stalls. i really do not know what to do. I have a bit of mods done to my car ive checked a lot of things. i also replaced the coil packs and spark plugs. replaced the DV. hasnt done anything. this only happens randomly though for me sometimes it runs clean sometimes this happens, usually if i use a lot of boost while driving or accelerate really hard. I have the forge dv and spacer, 3 inch turbo back no cats, autotech fuel pump, forge cold air intake and apr stage 3 software. i can not figure it out its extremely frustrating! helpp! haha


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## psychlow (Sep 21, 2006)

*Re: MAF/rough idle...HELP! (observer)*

I vote for lean misfire caused by a partially plugged/faulty injector.
Without the MAF sensor plugged in, ECU changes to a richer fuel table for safety since the ECU can't meter the incoming air.


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## saaber2 (Jul 15, 2008)

*Re: MAF/rough idle...HELP! (observer)*

How many miles? Dirty intake valves/fuel injectors/tumble flaps? VW says in their own patent that the valve deposits cause misfires and numerous other problems. Have you already done the valve cleaning and/or cleaned the injectors?


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## teeOHkay (Feb 22, 2008)

*Re: MAF/rough idle...HELP! (saaber2)*

i have 35K on the car and I just again had the car brought in and checked for vacume leaks, a couple of tiny ones were fixed but the car still seems to have a problem. All the coil packs/ spark plugs were checked, MAF cleaned out they cant seem to pinpoint it either. They are hoping another code will show up. Reprogrammed after a loose DV code showed up and that seemed to help a lot by fixing that vacume leak but there still has to be something else.


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## GolfRS (Feb 4, 2006)

*Re: MAF/rough idle...HELP! (teeOHkay)*


_Quote, originally posted by *teeOHkay* »_i have 35K on the car and I just again had the car brought in and checked for vacume leaks, a couple of tiny ones were fixed but the car still seems to have a problem. All the coil packs/ spark plugs were checked, MAF cleaned out they cant seem to pinpoint it either. They are hoping another code will show up. Reprogrammed after a loose DV code showed up and that seemed to help a lot by fixing that vacume leak but there still has to be something else. 

Please read this thread and contribute any way you can.
There is also some contact info you might wanna take notice...
http://www.golfmkv.com/forums/showthread.php?t=112990


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