My 83 Camaro with stock 305 and crossfire TBI injection runs good (just passed smog inspection).

However, when started in the morning, idle goes to about 1200 RPM, then over the next several seconds ramps up to around 1800. After a few minutes when the ECM goes into closed loop, the idle drops down to around 1100.
Obviously the ECM is getting some bad info. There is no "CHECK ENGINE" light and there are no stored error codes in the ECM.

The engine has a new TPS, MAP and O2 sensors. I've checked vacuum lines and they all appear to be in good condition.
Any other ideas of what could be causing this?

Thanks,
-rod

 

even 1100 rpm is a tiny bit high. try doing a simple idle decrease and drop it down to about 800.

 

Hmmm. I'll take a look for the idle adjustment.

Everybody said the idle is controlled by the computer, and the way the idle speed starts ramping up after start certainly seems like a computer thing. It sort of goes up a little then pauses, then goes up a little more then pauses. It's kind of "hunting" for an appropriate idle speed.

A few days ago I went to start it up on a really hot afternoon, and it actually didn't do the racing thing. It started up and idled nicely instead of like it does when it's cold.

 

Being that it idled good on a hot day, you may want to check the Engine Coolant Temp, ECT (not the temp gauge sensor) and Air Intake Temp, IAT sensors as they may be sending the wrong data to the computer. These sensors work toghether. Also check the idle control valve , if your car uses one, make sure it is clean and not sticking.

 

Hmmm. Now that's some good advice. I didn't even know there was an Air Intake Temp.
How can I tell the difference between the Coolant Temp sensor for the ECM and the Temp sensor for the gauge?

Is the Idle control valve the IAC (Idle Air Control)? It's got two since I've got two throttle bodies.

Thanks!

 

The ECT is located iether on the thermostat housing (TBI) ,or on the front of the intake manifold (TPI). The IAT sesor lives underneath the plenum, and the plenum has to be removed in ordr to get to it.