Did TBI IAC relearn and idle drops from 1200 to 650. Restart engine and idle goes back up. Change IAC and relearn again. Same thing. No vac leaks. Excellent fuel pressure. Fuel pressure reg is good. Throttle stop screw has never been touched. ECU issue? Thanks

 

Was the engine cold during iac setting?
can you datalog?

 

Hello. Initial relearn was cold. 2nd relearn was after it had warmed up. I do not have Data Log capability. Thx

 

Was this a problem before touching throttle blade adjustment screw ?
if it was and no vacuum leaks could be cts false readings. Can ohm cold and hot to see readings vs coolant temp. Datalog wil see iac movement and cts the ecm is seeing.

 

Sorry. Changed CTS as well and no change. Forgot to add that detail. Throttle blade screw has never been touched. Thx

 

Changed hermostat as well. Thx

 

i went though the same thing with an lt1 car. it wanted to idle at 1100 or so. i plugged off all vacuum stuff and swapped out most of the related sensors with known good components, even injectors and tb. wound up being the ecu. not saying that will be your issue, but it was with me.

 

What year vehicle, and which vehicle? The '88 - '92 F-Body TBI cars don't have an IAC learn procedure. There is a minimum air setting, but need to adjust the idle stop screw to achieve this.

RBob.

 

While it may not technically be a relearn, I always short A-B on the ALDL connector, turn the key on and let the IAC fully seat when I install a new one or make engine changes.

 

Actually working on a 90 Silverado guys. Thought it was same as the TBI set up in my Camaro. Apparently they are not. Thanks for the responses.

 

What kind of IAC relearn are you doing? A '90 should have the regular/standard C3 TBI ECM. It will likely do an IAC reset/calibration at key-off after the engine has been running. But not much else.

I do know that the f-body '8746 ECM won't control the idle speed until the engine is up to temperature. IIRC, the truck '7747 is the same way. Up until then the max idle speed is limited, but can still be rather high.

RBob.

 

The relearn on the Silverado is to jump the AB ports. Wait 30 sec. Then unplug IAC. Turn key off. Disconnect AB jumper. Start engine and warm up. Shut engine off. Reconnect IAC. This procedure brings idle to normal. But the next time the engine is started the high idle returns. I've ruled out the IAC itself by replacing it. And coolant temp sensor and thermostat. Thanks

 

missing a few steps there !