what's up all
I have been zapped before so let's get it all out in the open
I have third gen drive in a first gen camaro
complete tpi swap oe harness and ecm
also a 700r
here is my question, my scanner {snap on 2500} shows p-n in park and an
immediate change to drive when shifting out of park
however my iac does not step or change at all which causes a low idle sometimes stall, otherwise the iac functions normal, a/c switch etc.
am i crazy or should the iac not change with the shift from park
thanks any help would be most appreciated

 

wow all this time and knowledge and still no help
am i getting the cold shoulder

 

The ECM doesn't read what the IAC is doing it only commands it to do something. You have a strange problem.

 

strange problem indeed
i understand the communication protocols the scanner reads what the ecm commands, and the input the ecm sees from its various sensors and switches
when the ecm sees park to drive which my scanner shows it is {unless i am mistaken of where the scanner gets its info}, when the ecm sees park to drive it should command the iac to retract therefore more steps, unless again i am wrong about the ecm's control of the iac when changing from park to drive
strange problem indeed

 

Does the scanner see an increase in load?

 

it does see an increase in load but the lag time is to long before the iac compensates which leads most times to a stall

 

has this always done this? is the pintle in the iac at the proper depth max 28mm

 

since this is a new build and this is my last hurdle i have to say yes
i have done all the obvious clean t/b replace iac installed correctly..., all other functions appear normal as does readings on scanner.., iac shows when engine at operating temp around 0 to 5 when a/c activated raises steps as should... one step further if i turn the a/c on and immediately shift to drive all is well
the orange black b10 is connected and working as described 12 volts open in drive 0 closed in park.. it is not wired to disable starter since that is a separate circuit in this build

 

What type/year TPI system is installed?

Later ECMs had a PARK adder for IAC counts (steps) programmed into the binary file, earlier ECMs had an engine RPM adder programmed for PARK.

One caveat is that IF the ECM expects a given RPM and the engine is in compliance (equilibrium), there will be no IAC activity. It's a simple PID loop, and if the process is at the setpoint, there's nothing for the output to do. When the gear selector is taken from PARK, the ECM should expect some RPM drop (and is programmed to "forget" the PARK adder RPM). As long as the engine RPM is at the target idle RPM ± the allowable tolerance (also a programmed value), the IAC will not have to move (equilibrium again).

I'm guessing that the ECM is "happy" with what it is seeing as inputs. That said, the IAC might be less active than is normally be expected, causing some lag or "laziness" when it is called upon to move. Verify the throttle minimum air position is correct and TPS voltage is correct so that the IAC is always active. Having too much throttle plate opening will cause the IAC to shut down completely trying to lower the idle RPM. Asking the IAC to open quickly to recover idle RPM from a completely closed position could be what is causing your stalling/stumble.

 

Thanks vader you set the bar for all others in this board
The tpi is a complete 1986 maf setup.
I installed oem harness and original ecm [165}, however in search of an answer for this problem and others, maf codes etc. I replaced the ecm with a reman and the prom installed was a thermomaster and it was replace with what was apparently the last remaining gm oem in the us. The maf codes and problems went away. There has been no change however with the iac operation.
I may at this point go back to my original thought that the trans, torque converter
was causing to much initial load from park to drive and the engine, iac, could not compensate. There is only this problem when shifting from park to drive or reverse, after that everything is normal. I have gone through all the settings min. air, tps, timing etc.
Thanks and any other thoughts opinions or experiance's would be greatly appreciated

 

HELP!!!! OK NEW INFO
while going through all the settings today min air timing tps etc. i found with the est connector unplugged while setting timing when shifting into drive there is no stall, idle down etc, so what as so far as timing could be the fault, not adjusting timing fast enough? any ideas? help

 

I don't have an EST module to disconnect, but i do have an ESC module on my '88 TPI. When setting initial timing I disconnect only one wire, "Set timing Connector". IS EST and ESC the same thing?

When I data log I start logging before starting the engine. The IAC is shown parked at 160 steps once the engine starts, the steps decrease to zero, and then increase to about 20 when put in drive with brake applied.