When I stop the car somewhat fast, the RPMS will drop to about 500 and then the car will litteraly rev to 1500 and then idle back down to what I have set at 675.

At first I thought this was the decel enlean or DFCO so I set those values to only operate about 1200 and that didn't change anything.

Is this a timing or and IAC issue? Or something else?

It's driving me nuts. I have to make sure I have depressed the brake well or I will lurch forward 5ft.

Sometimes It happens when I put the car in gear. It will drop a few RPM then rev up and after the rev up it goes back to idle and is fine.

Thanks for any directional!
-Paul

 

What ECM and Mask ID are you working with. I would think id be looking for a way to add a few IAC throttle follower Steps. either that or your setting the Stall spark params off and thats why your getting the big jump. the last but not least is the TQ converter clutch maybe hanging on that will cuase a very anoying surge like you describe.

 

Assuming the IAC is set correctly, and no mechanical ills.

Your probably hitting the stall saver.
If you look using the words power steering you'll probably find some items for keeping the engine from stalling. Sudden heavy steering inputs can load the engine down enough to stall in some applications, so GM usually runs an idle routine so that at low rpm if it sees a stall coming it yanks the IAC open a little.

 

I had a similar problem recently. Mine turned out to be a sticky IAC that would sort of "pop" into place when a severe idle correction was needed during a hard stop. It even surged a little when using the AC, even when the IAC adder steps were dropped quite a bit in the chip. I took the IAC off and cleaned it as best I could, set the AC on IAC steps in the chip, and things have stabilized for the time being. If it starts it again, I'll replace the IAC as a more permanant fix.

If the IAC doesn't seem to have problems anywhere else (cold start surging, AC/DEF operation) I would start checking for vacuum leaks. If it only does it when the brakes are applied, I would start with the power brake diaphram, the vacuum line running to that diaphram, and the one way check valve in that line to make sure they all hold vacuum.

 

I have the 1227165 ECM running with a Modified ARAP Bin $6E Mask

It seemed to be the TCC clutch because with the TH350 transmission and non lockup stall it doesn't do it.... except when I start the engine warm. I have to let it idle for 20-25seconds when it's warm/hot before I can put it in gear or it will stall.

Thanks for the TCC look. Makes much sense.