00Silver

Hopefully someone can point me in the right direction...

Today on my way home from work, my GM developed a bad shudder/stumble on light acceleration, steady speed, and sometimes while sitting in gear at idle. If I put my foot into it, it clears up and seems to run fine. It also goes away if I put it in park or neutral. The "foghorn" sound from the airbox has also returned, and it almost seems as if it may be related to my shudder issue. I say this because the only time I noticed the shudder while sitting idle, was when the "foghorn" sound was happening. The spark plugs in the car only have around 5k miles on them, all 8 coils only have maybe 100 miles on them, the IAC was cleaned 2 weeks ago, and I'm not getting any CEL or codes. If anyone can point me in the right direction on where to start looking for a problem, I'd greatly appreciate it.

R.S.LOGAN

Could have a quick check on all vac hose / pipes for any leaks .

00Silver

Could a bad IAC gasket cause this? A buddy of mine had it apart 2 weeks ago and he had mentioned that the gasket has seen better days.

R.S.LOGAN

If it's drawing air , it wont help .You could make a new gasket from gasket paper if not able to get to parts / supplier store and eliminate that possible cause .

00Silver

Took it for a short drive and the CEL came on...Had autozone scan it, and he told me I have a misfire on cyl. 4, and both downstream o2 sensors are throwing codes. The temp. here is 7 degrees with a windchill of -14. Could this have anything to do with it or should I swap out the #4 coil and/or plug? The parts store guy said the fuel line to that injector could be froze up...but I've come to learn not to believe everything you hear at the parts store.

Bert

I'd switch the coil with another position and look at the plug. It may be water in thehole around the plug too. Don't worry about the O2 codes yet.

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Bert

00Silver

Ok, I will try that tomorrow. Thanks

00Silver

Removed the #4 coil and plug...the threaded area of the plug was rusted/gunked up, but the rest of it looked normal, so I cleaned it off, re-gapped it, and swapped out the coil for one of the old ones I still had. VOILA!! No more stumble! Now if I could only find a solution to the foghorn sound from the airbox, I'd be in good shape lol. Thanks for the help guys!

Bert

Maybe it's not sealing very good. Thanks for the update on the misfire.

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Bert

Bajarider

BTW OO, you have a fuel rail that feeds each bank of injectors, not individual lines. Unlikely that they would ever freeze up. -14 degrees! Yikes!