wiweeds

Hi I was wondering if anyone could tell me how to set the idle on my camaro. When I have my car in neutral and its moving it idles at like 3k rpm. But when I am at a full stop it goes down. My tach isnt working so these are estimates.
Thanks guys

rgarcia63

Idle is set when the car is in park or neutral and not moving.

We need to know what you have under the hood.
You need a known good tachometer, or a precision tachometer if you want to be precise, no pun intended.
Verify initial timing.

dimented24x7

iTrader: (2)

Idle really isnt adjustable with a TBI engine by mechanical means alone. The most you can do is set the min air adjustment. Search the TBI board, there are some write-ups on the archives for checking this.

Also, its possible that the IAC may be dirty as well, and is hanging up.

As for the idle when its moving, the ECM doesnt control the idle when the car is in motion. What it does do is add something called throttle follower, which opens the IAC (idle air control valve) based on the throttle position and speed. If the IAC is dirty, it can hang open after the throttle follower and cause a high idle.

Youll have to take teh IAC out and inspect it. If the IAC is covered in gum and deposits, then it should be replaced.

wiweeds

ok that makes sense where is the IAC located?

rgarcia63

Do forget to check the IAC port for crud as well.
After you put it back in, turn the key on(, but don't start the engine) for a few seconds, then off so that the IAC resets itself.
Location:
On my '88 it looks like this one. Should be on the passenger side of TBI, it has a 4-wire connector.

davidearlcox

Actually, the OP would need an accurate tachometer, not necessarily a precise one.

The conceptual difference between accuracy and precision is as follows:

When shooting arrows at a target, all the arrows hitting in a tight grouping is a measure of precision. The distance between the tight grouping of arrows and the bull's eye is a measure of accuracy. Electronic equipment can be very precise while not being very accurate.

For this reason it is common practice for inexpensive Digital Multimeters, such as are available from RadioShack, to be marketed as "Precision" test equipment with little attention called to their accuracy.

dimented24x7

iTrader: (2)

The ECM will tend to do what it has to to get to its target idle speed, so its sort of a moot point to worry about the exact RPMs the engine idles at. Just make sure the min air is set correctly and the IAC and TBI are clean. Sometimes the older TBI bases get pretty sloppy as they wear around the throttle shaft, which leads to the throttle blades hanging open. This can also cause a high idle.

The ECM iself transmits some basic information once per second thru the ALDL, so if you have a cable and something like winALDL or TP RT, you can read the RPMs, and a few other parameters.

rgarcia63

Which is how I set my minimum air rate because it's the same rpm signal the ECM uses.

wiweeds

Well, what I did was let the car idle and unplug a few things to see what happened. The picture is what I believe to be the IAC, when I unpluged it nothing happened to the idle. Should I have expected any change? Also I unhooked a black hose from the back and the idle went higher. Not sure what to think sorry I'm new to this.
Thanks,
Matt

wiweeds

sorry about the double post but I took my IAC out and replaced it. I still have no change. Any thoughts?

dimented24x7

iTrader: (2)

Do this: with the key on, engine off, put a paperclip between the A + B terminals in the ALDL port (do a search, should be lots of posts on how to do this). Wait about 15 seconds, and then go disconnect the IAC. At this point, the IAC is now fully closed as when you put the paper clip in, the ECM automatically commands the IAC to close fully for testing.

Pull the paperclip out, and start the engine. At this point, the engine will be idling on only the air coming thru the TBI. Youll probably have to crack the throttle to get it to start, and the engine should idle real low, around 450 RPM or so. If it still has a high idle, then either the IAC is stuck open for one reason or another, the TBI is hanging open, or there is a vacuum leak.

henryd3

iTrader: (128)

The last post explains it well, but here's the article from the technical articles section, a good place to check out.
https://www.thirdgen.org/tpimod2