So let me start off by saying, I tried the best I could to tune the car based on researching everything I could on the forums here before I started to post this and what bits of knowledge I had from using HPTuners in the past. But at this point I'm just stumped and not sure what to do. Like the dozens of posts on here, I think I am having issues with the IAC motor and tuning. The issue as many have had on here, is the transition from Park to Drive gears. While in Drive or Reverse, the car stalls while idling after a few seconds in gear. I have a 1988 Trans Am GTA, rebuilt 350, and 2200 (I think...forgot) stall.
The 350 has aluminum heads, factory TPI (not ported), cam (specs below), new pistons, rods, etc but at factory compression. I have replaced the IAC motor, replaced the Narrowand O2 sensor with a 90-92 spec sensor (car didn't seem to want to go into closed loop without changing this), using an AC Delco MAP sensor from GM, and converted the car to the EBL P4 PCM. Before the PCM conversion, the car did stall on occasion but not nearly at the frequency it does now. Before trying to make any adjustments myself, I started by loading in the EBL_P4_3005.BIN as I wasn't sure what the EBL P4 came stock with loaded in the PCM, and the readme text file says the 3005 binary is for 350s with Automatics.
After doing some small tweaks like raising the idle rpm for Park and Drive gears, I started digging through the forums to see if I could find a solution to the stalling in gear. I came across the following thread below and applied all of the adjustments recommended in the thread. While these tweaks seemed to work for the original poster, I unfortunately do not seem to have the same luck. https://www.thirdgen.org/forums/diy-...le-issues.html
One thing I can say I notice right before the car stalls out in Drive Gear, is that the IAC count begins to climb rapidly from around 60 count to the max 140. If I put the car back in Park before it stalls out, it will slowly decrease back down to around 60. That's about the best insight I have as to what's going on, but I'm not sure what to do about it. I have attached the current tune I have in the car, and would greatly appreciate any advice anyone can give me.
There is a good possibility that the MAP is high when in gear. This will/can cause the ECM to believe the MAP sensor is bad and create a default value. Which isn't close to the real value due to the cam.
Can usually see this occur in a data log, if the MAP is above 68 KPa (the supplied value), the ECM flags the MAP as bad.
Set this parameter about 10 KPa higher then what the actual in drive idle MAP is:
RBob,
I tried it out last night, that fixed it! Thank you so much, I can finally start driving this car around and tuning it!
One question about the IAC step counts. Is it supposed to max out when you are in a Drive gear? In Park it's around 88, which I think is too high as well? But when I put it in Reverse or Drive, it just continues to climb to the max value.
Open the throttle blades until the IAC count is in the 20 - 25 range. Do this on a warm engine with no other loads. Keep an eye on the WUD idle indicator, if the ECM drops out of idle (increasing TPS), key-off for ten seconds, restart, let engine settle and continue.
As you tune, the idle stop screw may require some further adjusting. The TPS is OK as long as it is between .3 and .7 volts (at closed throttle).
As for the IAC increasing in drive, may find that a handful more spark advance (SA) will help with that. Along with forced open loop idle and leaning it out a little.
Hi RBob,
I'm just getting back to this after a few weeks of many other things getting in the way. Before even doing any IAC adjustments, I did take it out for a drive just to see what it would do and the car drove great.
But today I just got to adjusting the IAC count as you said, and I successfully was able to get the IAC count at idle around 20-25. I originally had the P/N idle set to 800, and while adjusting the idle screw I could not get it lower than 38. So I lowered the P/N idle and Drive idle in the PCM to 700 rpm, and then adjusted the screw more. That seemed to allow me to get it down into the range I needed. Once I had adjusted the PCM's idle rpm to 700, the IAC was actually too low, at 0, so I was backing the screw out until it reached the 20-25 range. Anyways so that is done.
However, the Drive gear IAC count is the next thing I need to adjust. So I'm noticing it maxes out when I put the car into any Drive gear. I know you said to increase spark advance and possibly set it for open loop idle as well. My question is, what should the IAC range be in Drive gear? Also, how do you set it for open loop idle in Drive?
