High idle

[tmkassin]

exxfire is in the neighborhood, but I think adjustment of the idle stop screw is the last thing to check, ESPECIALLY on a new TB. You haven't adjusted already, it have you? Some people do this to compensate for an undiagnosed problem, but that is not the right thing to do...

750 warmed up? STEADY 750???

IAC stepper count at 0 means the pintle is max'ed into the bypass port, and is blocking all air through the IAC controller. It's stuck with carbon fouling, OR, there's a vacuum leak (not likely, since you say it's steady when WARM), OR, ECM is sending a faulty signal, that's keeping IAC pegged, OR, ECM to IAC harness is shorted of open... Last possibility is the adjuster screw is too far extended, holding the butterfly open too far. Again, I think if you have NOT already adjusted this, it's probably where it is supposed to be

Pull the IAC, work GENTLY the IAC pintle shaft. Feel for any 'grit' that's impeding the action. Spray in some THIN lube, and blow it through with compressed air, or a vacuum attachment, to pull the excess.

Re-install, and watch the stepper count on a scan.

If still at 0, pull it again, and test the IAC connector voltage, like so:

Block the IAC port with tape or something, making sure you see how you're blocking it - since this is what it's doing anyway, with a 0 count.

With it out, port blocked, get the spec IAC VOLTAGE at idle from FSM, and put your multimeter on the IAC connectors while it's idling. Look for variation as you work the throttle linkage.

If it dies show voltages at or near spec, connect the IAC to the connector (with the IAC port still blocked), and see if you get pintle movement while working the throttle linkage.

FSM test for IAC function, and voltages might be slightly different here...

Using the scan tool I can see the IAC counts changing as it idles down. When I stop it is idleing around 1200 and the IAC steps down till the idle is around 650. But it will not do this till I am completely stopped. At that point the count is about 14 if I remember correctly. It is a new IAC in a brand new throttle body. The car runs flawlessly other than the idle issue.

[tmkassin]

New injectors, IAC, EGR, TPS, plugs, wires, MAP and a 52mm throttle body. Now today a left oxygen sensor. BINGO! it finally idles down. So I spent a little money trying to figure this out. And I was looking for any excuse to get the 52mm throttle body. It was still much cheaper than the dealership and I got a real education. The injectors were necessary too. This car runs fantastic now.

[shortej]

New injectors, IAC, EGR, TPS, plugs, wires, MAP and a 52mm throttle body. Now today a left oxygen sensor. BINGO! it finally idles down. So I spent a little money trying to figure this out. And I was looking for any excuse to get the 52mm throttle body. It was still much cheaper than the dealership and I got a real education. The injectors were necessary too. This car runs fantastic now.

Now just for clarification, when you say left side, is that drivers side or passinger side? The reason I ask is I have the same issue with with my 94 coupe, and I have replaced the drivers side already for a rich condition, the passinger O2 sensor code went away after I changed the drivers side. Wondering idf I need to change the passinger side as well? Thanks ES

[tmkassin]

I ended up replacing them both. It still idles about 1000 when cold and 750 when warmed up. Not the right numbers according to the FSM. I even re-set the min idle screw according to factory specs. It is way better than 1500 when cold and 900 when warmed up. I think it has to do with my airbox and exhaust mods.

[John Lupulio]

Nice car have high idle problem been through my 88 corvette my mechanic too its crazy idles 1300 disconnect mas air runs like have cam high performance connected mas air idles back up to high rpms everything is good car no leaks ecm new injectors 58mm throttle body air control motor no vacum leaks ect.....