72Z/28

Hello

I have been struggling to sort out the stalling and engine dying when AC is on while revving the engine or dying while slowing down before stopping at stop light. This issue has been there before and after tuning that was done on the dyno last month. The RPM was set at 750 when tuning done.

So last week, I did the following on the car:

-Replaced the rope seal between the shells of my FAST 92mm intake along with port seals to rule out vacuum leaks

-Replaced my stock 75mm TB with new FAST 92mm TB and put new IAC, MAP,TPS sensors

Yesterday, I did the TPS/IAC relearn. Adjusted the Tb screw and set the TPS to 1.96% as the next value was jumping was 2.35% instead of 2% and the voltage reached 0.82v.

I started the car yesterday and waited till it reached operating temp. The car started idling at 930rpm, which was higher than what was tuned at (750rpm).

Also, noticed idle hanging at 2000rpm for a few seconds. Even if rev it beyond 2000rpm, the idle drops to 2000rpm and stays there for a few seconds then it drops to 930rpm.

I ran out of ideas and will be thankful to new ideas/checks to be done

unfortunately I do not have an HPtuner to do data logging. I am just using ultragauge OBD2 scanning tool to check TPS% but nothing about IAC counts and stuff

Bogan Edition Z28

Can you disable throttle cracker with that software? Try that. I had similar issue and it fixed my issue. I set mine to come on at 100mph and off at 98mph or vice verse.

72Z/28

The only thing this ultragauge OBD2 can do is clearing codes. I cannot do anything else.

Kfxguy

iTrader: (1)

the voltage is supposed to be around .60v, 0% throttle.

72Z/28

Is 0.6v for stock engine? I have 68 camaro with cammed LS6 engine. Does this mean that the TPS is faulty or it needs to be slotted in order to adjust the voltage? It is a new TPS that came with my FAST throttle body.

Kfxguy

iTrader: (1)

Stock. Modded. Turbo. Supercharger.....it does not matter. The voltage needs to be set within a range. Doing a tps "reset" is a sham too. When you turn the key off, it resets to zero.

You cut the nipple off and slot the holes and adjust it where it needs to be. Idle tuning a cable drive throttle body is quite involved....if you need me to walk you through it, I can. My idle tuning procedure is quite involved because I have to have mine be perfect and not just idle it up high like some people do.

72Z/28

well, I did adjust the screw on the TB to lower the TPS volts and Idle rpm dropped as well. So when KOEO, the TPS voltage is 0.79v. However, when the engine is running, the TPS voltage reads 0.62v.

is this normal?

Kfxguy

iTrader: (1)

Maybe the TB is sticking? It might fluctuate .02-.04v but not what you are seeing. some tps (non factory GM) are wonky. Sometimes they will cause you headaches. Sometimes its a balancing act to get it to idle, my suggestion to you is force close the iac motor with your scanner. open throttle blade until you can get it to idle, about 100-150 rpm lower than your target idle. Then adjust the voltage on the tps. If it changes the idle (balancing act) then tweak the throttle blade. Remember, when you shut the engine off, the tps resets back to 0%....no need to do that stupid tps reset. Then when you get it to half *** idle with the iac closed, you can work on the rest of it. If you put a cam in, thinking you can just adjust the blade and the tps, aint gonna cut it. Timing reacts faster than the IAC, so you'll rely less on the iac for throttle dips than you think you will. Timing will also cause the rpm to drop very slow or very fast.

72Z/28

Thanks for the valuable input man. Unfortunately, all I have is the ultragauge obd2 display but it does not have any indication on IAC position.

I am using the TPS that came with my FAST TB but I do have one from GM as well. i am going to install the GM one and see how it goes.

Otherwise I need to take to a tuner. I was just trying to resolve the engine stalling/ dying issues when AC is on and the compressor clutch kicks in

72Z/28

Ok, just removed the TPS and IAC that came with the FAST throttle body and put back original GM ones(new). In fact, the GM TPS response while moving the throttle linkage was smooth and the volts are properly increasing at an increment of 0.01 till reached 4.5v at full throttle. Much smoother than the FAST TPS.

The GM TPS volt was at 0.62 when KOEO. However, it dropped to 0.39-40v when engine was running at operating temperature.

I guess there is an issue with the tune itself.

Kfxguy

iTrader: (1)

The unfortunate thing is I really cant help you if your arent able to tune or flash the ecm. Theres not alot you can do. If its been tuned before with this cam, and started acting up, then maybe you can fix it, but if it hasnt been tuned, then I dont see you nailing it down without being tuned.

72Z/28

I hear you man. I think I need to get me an HPtuner to start looking at the data, then it would be helpful for you guys and for me to decide on what changes to be made.

I do appreciate your time trying to help me though.

72Z/28

Ok guys I guess the reason why my TPS voltage was off by .20 volts was because when I used my multimeter to measure voltage, I put the negative alligator clamp on one of the bolts on radiator support.

I have found a post in one the forums that it is better to probe the negative wire into the TPS negative wire on the connector. So gave it a trial and my TPS voltage was reading 0.55v when KOEO and 0.54-0.55v when engine running at operating temp.

so I adjusted the screw on TB so the TPS voltage to be at 0.60v when KOEO & 4.43v at WOT. It reads 0.58-0.59v when engine is running.

Also my idle rpm increased a bit and it is idling at 850-900rpm. At this Idle , the engine does not stall or die while revving the engine when AC is on.