I'm setting the minimum idle on my 3.1. OK, I jumper the ALDL for 30 seconds and then disconnect the IAC. Using my scantool, I look at the idle and I can't get my idle below 700 rpms even though I backed out the idle screw all the way. Also, since the IAC was disconnected, how come the scantool showed the IAC counts at 13?! Am I missing something? I powered down the scantool and back on to refresh the readings so as not to get any old values. Once again the scantool showed the IAC at 13 counts. And on top of that, the car ran for over a minute and the SES NEVER came on while the IAC was disconnected. Bad ECM , scantool or IAC wiring?

Ken

 

Disconnected IAC will NOT throw a SES error unless the IAC is disconnected when open to, say, the 2000+ RPM range, where the ECM throws a code 35 for uncontrolled idle speed.

Did you jumper the ALDL with the engine running or not? Do you have any vacuum leaks that you know of that could let in extra air? Try cleaning the IAC and throttle body, particularly around the throttle plate, and replace the TB to plenum gasket.

Does your scantool have a "Hold Idle Speed" setting? If it does, test the IAC using that, since your scanner is obviously not a Tech I, which allows the user to manually control the IAC opening and closing.

Check your MAP reading as well as the CTS and O2S readings to see if there are any other problems (running lean or rich... lean can indicate a vacuum leak).

 

The steps I took are like this:
Jumpered the ALDL (key on, engine off)
Waited 1 minute and disconnected the IAC.
Took jumper out of ALDL and started engine.
Backed out idle screw for air gap, then back in to barely hit throttle lever plus another half turn.
TPS was at .49 volts and RPM only went down to 700.
Turned engine off and reconnected IAC, then disconnected battery for 5 minutes to clear ECM.
Let cooling fan cyle, then engine off... waited 5 minutes and let the fan cycle again.

I've sprayed with throttlebody cleaner and cannot find a vac leak anywhere. The throttle body had been taken off prior to all this and completely stripped of carbon and oiled. New gasket as well.

The MAP was around 1.70 at idle and the O2 sensor went from rich to lean but always reading rich on the road. BLM still at 100 no matter what and the Integrator around 126 on the road. I'm thinking the EGR might be a little open, but I have taken it apart and cleaned it. ECM signals them to open while driving, but still could be bad.

Ken

 

Is there any way you can either do a snapshot or have someone cruise with you on the road to write down the numbers? We need the MAP, O2S, CTS, IAT, IAC counts, EGR cycle, power steering switch on/off, canister purge on/off and the TPS % numbers going down the road. Probably best on a flat road with cruise control engaged (if you have it and it works) so that the numbers are close to constant. Also need the knock retard if your scanner can show it.

Also, fuel pressure may come into play. BLM's are still out of limits on the rich side. Might want to test that with the gauge taped to the windshield or something to see what happens.

:edit: The INT is in the middle of the range (0-255), so I would think that's okay, but the FSM isn't giving me a direct range as to what's what. The MAP is on the high side of the idle range (1-2V), but that shouldn't be an issue. FSM says that a BLM of 110-150 at idle is normal and that it tends to follow the INT value. However, your BLM isn't following the INT for some reason.

Also, have you checked the on-road numbers with the canister disconnected and the purge line plugged?