help please
does the ecm use the input from the p/n position switch to operate iac
if scanner shows change from park to drive should'nt iac steps increase
thanks have been all over looking for an answer

 

Typically the Prk/Neut idle speed is higher then when in drive. And yes, the ECM usually bumps the IAC a few steps when the transmission is shifted from Prk/Neut to a drive position. This is to make up for the additional load to prevent the engine from stalling.

RBob.

 

ok but does the ecm use the p/n switch input or does it use load in other words
if my car is running at operating temp and i operate the switch with out actually putting the trans in gear therefore not creating a load but the ecm sees the change will the iac steps increase solely from the input

 

The ECM uses the P/N switch. Note that this is NOT the same P/N switch for the starter interlock. It is a separate switch.

Opening the switch should have the ECM adding a few IAC steps. At the same time this is calibration dependent. Without knowing which ECM & MaskId is being used there is not a definitive answer. But note that the idle control logic will set the idle speed by changing the IAC.

RBob.

 

thanks rbob
how can i determine calibration and maskid
the ecm is a 165 new reman and the prom is new gm dealer purchased

 

Which year is the calibration for? F-body TPI?

I didn't recall the '165 MAF calibrations having an IAC bump so double checked. Neither the $32 or $6E mask appear to use an IAC bump when the trans is shifted into drive. There is a change in the desired idle speed. Two that I checked are 50 RPM higher in Prk/Neut, which is on par for other GM ECM strategies.

That is, higher idle in prk/neut then in drive. Prevents the engine from stalling when the transmission is shifted into a drive position.

RBob.

 

thanks again rbob now for something completely different {monty python}
noticed with the est timing connector unplug there is no idle loss when shifting from park so i guess that rules out possible torque converter lock up seems to be some sort of a timing issue, which i have check and double checked and every thing is in spec, not sure what to do next but i will keep on hammering thanks