# Missfire problem



## SlimQuattro (May 15, 2008)

I've been working on a 01 a6 2.8 auto for a friend of mine. The car would start misfireing when the ac was on so I vag comd it an got acode for faulty secondairy air injection, misfire on cyl #1, and random multipul missfire. I changed the sai pump,replaced all the accordien pipes, plugs wires, fuel rail all 6 injectors and tried 3 sets of coil packs. I drove the car for a while an it had a slight hesitation but no check engine light no codes. He called me yesterday saying it's now doing it worse with an without the ac on. Could it need a maf sensor or fuel filter?


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## O_o (Nov 12, 2009)

[/quote]Could it need a maf sensor or fuel filter?[/quote] 

It's possible. Try unplugging the MAF sensor and see if that helps. While you're at it, clean the throttle body and air filter. 

If that's not it, there are a gazillion other things that could cause a misfire, but most of the time it's because there's not enough fuel, or a weak spark. Do you still have the cyl. 2 misfire code, or is it just random? Does it always misfire, only at idle, or only under load? Can you check the fuel trims, or are there any rich/lean codes from the O2 sensors? Any smoke/vapor coming from the exhaust? What's the fuel pressure at the rail? Did you test your alternator? Do you have a nice bright spark? Did you do an impedance check on the coils? Etc...


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## dubluv3 16v (Aug 1, 2004)

i was working on a 99 passat today same prob. the lady washed it then a day or two later it missing. so i picked it up no light then when driving the engine light came on. scanned it, it said misfire cyl1 and low voltage to control module. replaced plugs and wires it seemed a little better but could hear valve ticking. checked oil none added three qts. tick went away sputter was almost gone. reset code then started driving back home light is on again and sputtering but just a little could it be cause the low voltage i tested battery and it was ok. maybe the alt weak i forgot to test that?


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## gregthebuc (Sep 26, 2009)

My '99 was doing something similiar not long ago. Found the Combi valve on the passenger side had a crack and the coil set off a light show after dark with a spray bottle. Replaced the valve, changed all the vac lines, cleaned the TB, and installed a new coil. Runs like a champ with 116,000 though I don't want to shout that too loud as it might hear me. lol


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## SlimQuattro (May 15, 2008)

the guys wife stopped by with the car the other day an she says it runs great on the intersate and when your in the throttle, but at low rpms and when backing up is when it misses.the guy never said any of that. i drove it an at 1800rpm it misses every time. she also said it didn't start doing it until he changed the coolant temp sensor because someone at advance auto told him it needed a new one. it's hard to tell what he did and isn't saying but if they bring it back i'll check the combination valve and vacum line on it


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## O_o (Nov 12, 2009)

Idle & low rpm rough-running/misfiring is usually due to a vacuum leak...


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