1986 tpi camaro 700r4
let me make this simple does the ecm use input from the p/n switch to operate iac or does it use load only
thanks

 

no p/n. simple enough? I saw the whole situation with a search and feel you. Most low idle stumble stalls happen cold because of intake leaks. you might get better help if you list operating conditions ie. happens when hot, happens when cold, happens every time i put it into reverse or forwards. Leaky egr's cause some stumble problems, intake leaks(mostly when cold), throttle too far open so iac can't do it's job, opening up the exhaust which makes the engine idle low, plugged catalytic converter, low fuel pressure, carbon in iac system, injectors not working(mostly when hot), ----do you see a pattern here. Most stumble stalls have nothing to do at all with a computer. the computer does it's best to compensate but there becomes a point where it can't do any more. I like your determination to get to the bottom of it, and know that you will-keep applying yourself-don't give up.
Note:I struggled with one of these on a vette and found the rubber below the little square plate on top of the intake was deteriorated and was causing a lot of the concern , leaked and blocked the port partially combined with a leaking egr. Good luck.

 

thanks ed
here is the scoop
new motor built by me completely
bored 327 2.02 valve 67 gm heads ported
69 z28 cam and springs
roller tip 1.6 rockers
engine to slow to recover when changing into gear no matter hot, cold, mad, happy
if shifting into gear with foot off brake so less load will sometimes be able to recover
no other running problems associated with this symptom,
thinking torque converter everything else is set within specs, iac min air tps timing etc
thanks

 

When shifting into drive a prk/neut switch helps a lot. The ECM uses a higher idle speed when in prk/neut then when in drive. This helps prevent the RPM from dipping and stalling. Some ECMs also bump the IAC open a few steps when it sees the prk/neut switch change to in-drive.

Note that the prk/neut switch for the ECM is separate from the prk/neut safety switch. The safety switch being to cut off the starter from cranking unless the shifter is in either park or neutral position.

If you don't have a prk/neut switch installed for the ECM, then leave the wire open. This is in-drive and better then having it in prk/neut all of the time.

RBob.

 

nice. I'll check a wiring diagram sometime to see how that works. didn't realize that ecm for that model had a feature like that. where are both switches located? normally? not in the trans, but on the console with the shifter?