Need Help with LT1 Trouble

[bigbadspoon]

Hi everybody. I'd like to bow before the wisdom of the more experienced members on here and ask a question about my 94 Z28. It's got an aftermarket cold air induction and some base-level exhaust mods, and now the idle is very high (1200-1600 in neutral) and my mileage has been shot from about 20-22 mpg to about 11-13.
I was, needless to say, concerned about this, and so took the car to a mechanic, where I was told that the computer needed to be reprogrammed to compensate for the aftermarket parts. I thought that sounded kind of strange, because the mods are light and the computer shouldn't have trouble, but I called around to find someone to do the job anyway. Since I couldn't find anyone in the entire city of Orlando, FL capable of such a job (stupid, huh? There's 1.6 million people here; someone should know), I wanted to ask if anyone else has experienced this and what they did about it.

[Craig 94 TA GT]

There is most likely some other problem that is causing your idle to be at 1200+. I've had a cold air kit, exhaust, etc. for a long time and they didn't do anything to my idle...and hardly much to my mileage. Something else is forcing your computer to idle high. I would say, if you can, buy an ALDL cable (about $50 shipped, on ebay - or $90 everywhere else) and read the data from your PCM. I would also suggest cleaning the IAC (on the throttle body) but I don't think that would also cause a bad loss in mileage.

Did you ever see the SES light kick on? Are there any kinds of misses or hesitation when you drive?

[TraceZ]

Hi everybody. I'd like to bow before the wisdom of the more experienced members on here and ask a question about my 94 Z28. It's got an aftermarket cold air induction and some base-level exhaust mods, and now the idle is very high (1200-1600 in neutral) and my mileage has been shot from about 20-22 mpg to about 11-13.
I was, needless to say, concerned about this, and so took the car to a mechanic, where I was told that the computer needed to be reprogrammed to compensate for the aftermarket parts. I thought that sounded kind of strange, because the mods are light and the computer shouldn't have trouble, but I called around to find someone to do the job anyway. Since I couldn't find anyone in the entire city of Orlando, FL capable of such a job (stupid, huh? There's 1.6 million people here; someone should know), I wanted to ask if anyone else has experienced this and what they did about it.

That is BS about needing a new program.

Check your throttle linkage for a hang up. Disconnect the cruise control cable and see if that changes it. Make sure the throttle blades are closing completely. You might want to remove the throttle body and clean it up really well. Put new gaskets on it and clean up the Idle Air Control really well. Also check for vaccum leaks. Also make sure the intake ducting is securely on the throttle body all the way around. It is a common mistake for folks to not get the intake elbow on the bottom properly.

If that does not help, I'd get it scanned and see what the values are for the IAC and the TPS.

[Joe 1320]

yep, it's BS alright.

A good chance what was mentioned already could be responsible. The IAC is directly responsible for metering additional air into the intake when the throttle blades are closed so that could be affecting idle. So could a restricted throttle cable. The actual target idel rpm is programmed into the computer, but other circuits have an influence.

[Jeff_in_Atl]

Wasn't there something somewhere about the oil from the filters like K&N getting on the MAF wires and causing this. I think Kerm posted a TSB from GM about this.

[Joe 1320]

Over oiled replaceable filters (K&N) can cause fouling of the MAF sensor element wires. If this is suspected, electronic contact cleaner can be used to clean the MAF internals.