I know the ECM does, but what signals the ecm???
Most of the time she idles at 1000rpm, but has, at times, recently, started to idle at 700 rpm. (warm)
When it is at 700, it will climb back up to 1000 in a short time. But, also may cause a stall. 3.4, 86gt, automatic.
She does have a new IAC.
Ideas???? Thanks

Edit.. No codes.

[This message has been edited by Dan010 (edited 11-19-2003).]

quote Originally posted by Dan010: I know the ECM does, but what signals the ecm??? Most of the time she idles at 1000rpm, but has, at times, recently, started to idle at 700 rpm. (warm) When it is at 700, it will climb back up to 1000 in a short time. But, also may cause a stall. 3.4, 86gt, automatic. She does have a new IAC. Ideas???? Thanks Edit.. No codes. [This message has been edited by Dan010 (edited 11-19-2003).]

Idle speed (RPM, CLT and TPS and I think MAP and VSS also contribute.
IAC counts in steps, srews a pintle into a bypass hole in the TB.
The TB can get pretty gunked up by the EGR. I would remove the TB and clean it to see if that helps. Has the TB adjustment screw been messed with? If it is at 700 rpm for more than 30 seconds, it should set a idle speed error code......Paul

The ECM receives signals from several sensors. The first would probably be the intake temperature sensor on the air filter canister. You also have the throttle position sensor, the O2 sensor, the coolant temperature sensor, the MAP sensor, and finally there is an oil pressure and tachometer trigger signal. All of these tell the ECM what the outside conditions are so it can adjust the IAC and they also tell it how good the engine is running and if it is running. The ECM reads these variable and adjust the IAC to compensate for them.

This ought to be fun, throttle body should
be some what clean, but will check/clean.
Any quesses to which sensor would be the most likely one to check first??? then second.. ect???

quote Originally posted by Dan010: This ought to be fun, throttle body should be some what clean, but will check/clean. Any quesses to which sensor would be the most likely one to check first??? then second.. ect???

As a vacumm leak causes a high idle, a restriction in the IAC orifice may cause a low idle. (Could also be WAY retarded timing) The IAC would then step out until it gets to desired idle.
Those TB's can get REALLY gunked up from EGR gases (carbon). I would start cheap, by cleaning the TB and IAC passage, and make sure IAC tube to lower manifold is clear, before I would throw money at replacing sensors. The only real pain to removing the Tb is the coolant lines to them (which IMO are useless)......Paul

clean the throttle body for sure. I would also take a look at that TB adjustment screw. My buddy messed with mine one day because it was idling a little high (but the car had just been turned on) and after that it gave me a stupid code. It hadn't done it before so I just adjusted the screw back. If you still have a problem after adjusting it then its probably something else. But don't go replacing sensors like crazy, you might just be wasting money.

I'm glad I found someone who is having the same problem I'm having with my 86 SE, 2.8, except its the exact opposite. I can not get the rpms on mine below 1400. I have done everything posted on all the replies to this topic and then some!! Checked the PCV, removed the TB and cleaned out with TB clearner and blew out with compressed air. Checked all vacuum hoses/lines for cracks. Removed the EGR tube and inspected for hair line or other type cracks. Replaced all the gasgets for the EGR. Tested the EGR itself with a vacuum pump. Tested and inspected the emmissions canister. I was getting a SES code of 32. Ended up being the solenoid located on the right side of the engine, next to the Thermostat housing. I have also replaced the TPS, Coolant temp sensor, O2 and MAP sensor. The only sensors I have not replaced are the IAC and the one which goes connected to the air filter canister. I stopped receiving SES codes and noticed a little better gas mileage, but I still can't get the rpms down. Does anyone know if the IAC or the air filter canister sensor would cause the hight rpms? I'm really frustrated. Any suggestions will be greatly appreciated.

With the engine running put your finger over the IAC hole in the TB...if your engine keeps running you have a vacuum leak somewhere....I had same problem and mine was the lower intake manifold bolts came loose and messed up the gasket...

jgonzales

I am having the exact same problem with my tired 2.8 It's frustrating. I have replaced exactly the same stuff you have including the IAC, but not the air canister sensor. So I am also interested in what people's thoughts are. And I do have the IAC adjusted correctly. So this means to take the IAC out, and plug it with our thumbs and see if the car dies. If it does'nt then what?

no dont take the iac out, there is a hole in the TB just outside of the throttle plate. cover that.