I've got a '94 Z28 with 52,000 miles on the clock now and I put some Pacesetter Longtubes on about 5-10k miles ago. With the headers came new plugs and wires. Soon after I did fuel filter and other fluids plus brakes, pcv valve and blah blah blah. I never noticed a slightly rough idle until recently for one reason or another I hadn't done anything differently I was driving through a neighborhood around 25-30mph and the RPMs were almost surging up and dropping back down again. It was the most peculiar thing. Once I got home I let it idle and I checked my wires and such, and it idled slightly rough, but nothing too out of the ordinary. I let it sit and went back later and drove it, and it seemed fine.

When listening to the exhaust when I'm driving it still kind of sounds like it is surging, but the tach isn't moving from the steady RPM at where it is at. I've talked to numerous people, and they really aren't too sure as to what to think.

Today I was sitting a stoplight and I put the car in neutral and gave it a little gas up to around 2000 RPMs, and sure enough, I would keep my foot steady but the tach would bounce up 200 - 300 and drop back down. Same symptoms when I was driving around as well. My gas mileage has slowly been getting progressively worse since I put the LTs in, so I have a slight idea that it could be O2 sensor related, but I'm not positive.

Anyone have any experiences or suggestions as to what it could possibly be?

 

subscribing..

 

?? Don't quite understand

 

I would suggest replacin the IAC motor and cleaning out the TB for starts!

 

I cannot find anything about the IAC Motor in my Hayne's Manual. Any suggestions where I can find a writeup on it? Or is it pretty straight forward?

 

its very straightforward. Two screws hold it into the throttle body. I'd put a screw bit in there and turn the bit with a wrench to take it off without having to remove the throttle body. Its cheaper to try to clean it first as opposed to just replacing it.

http://shbox.com/1/iac3.jpg

 

It's straight forward but while your at it you should remove the throttle body and clean it as well, with the throttle body off it makes cleaning the IAC easy. And on a side note for whatever reason my car one day started doing the exact same thing your talking about. I cound't figure it out for the life of me so I went through my motor and tried to clean every little sensor, I took of the intake and put it back on and then I dis-connected the battery and let it sit over night, for whatever reason(not sure what did it) the car was fine the next day.

 

You removed the entire intake manifold? For what reason?

 

Sorry if that was unclear, I just removed the intake from the throttle body down, then clamped it back up perfectly. Sometimes if your air intake is just slightly off it can cause a funny idle.

 

you mean the intake elbow

 

yea, that thing

 

I gotcha. Alright, well I've got a check list of things to check. I'll be sure to let you guys know how things work out. Most likely I'll try that throttle body trick as well

 

yeah i have 74k on both o2s and teh IAC so its either or and neither have thrown an SES , i do plan to do both of em anyways