Idle wants to bounce and surge as motor warms up
09-19-2014, 02:21 PM
#1
Idle wants to bounce and surge as motor warms up So, I've had the car idle tuned and street tuned and was about to take it to the dyno but I've run into an issue where the car does not want to hold idle once warm. My tuner can't get back out to look at the car until Monday, so I'm looking for ideas on what to check/troubleshoot over the weekend. When it was tuned, it idled fine when hot?
Okay, so first things first, I am running in open loop SD. I replaced the MAP because I didn't have it secured on the back of the FAST and it was coming loose, so I thought it was an issue. I bought a new Delphi MAP and relocated to the front and plugged the hole in the back of the FAST. I took the manifold off and when I put it back I double-checked for vacuum leaks.
The car idles fine when cold (around 1050 RPM). But once it starts to warm up it begins to surge from 900-1100 and then it gets progressively worse if I leave it in park or in gear with idle until it dies. It's commanded to idle at 925 once at operating temp.
I've adjusted the TB set screw and reset the TPS several times.
I have a new fuel filter to try. I have a new Racetronix pump in the car.
I plan to take the IAC out and clean it.
I have a new LS3 MAF/IAT in the car. The MAF is disabled but the IAT is enabled.
I had a check engine light come on before I replaced the MAP and it's gone (will have to see what the log shows on Monday if it is MAP or IAC related).
I also plan to drive it today to see if it stumbles/surges under load in gear to rule out the IAC as being faulty.
Any other ideas for what to check? It was doing it before it was tuned. I mean it surged horribly and would die out quickly - and it had a mail order tune on it where it idled fine for about 5 minutes and then never idled right after that. So it's worked on and off and seems to stop working just because.
After the street tune, it idled and drove fine for about 2 hours during the process. Once we finished it had a high idle hang when I pulled it back into the garage. And since then it's been doing this **** while idling once warm. So it sounds like it developed a vacuum leak somewhere that only shows once warm? Because it idles dead nuts when cold.
Any thoughts?
Okay, so first things first, I am running in open loop SD. I replaced the MAP because I didn't have it secured on the back of the FAST and it was coming loose, so I thought it was an issue. I bought a new Delphi MAP and relocated to the front and plugged the hole in the back of the FAST. I took the manifold off and when I put it back I double-checked for vacuum leaks.
The car idles fine when cold (around 1050 RPM). But once it starts to warm up it begins to surge from 900-1100 and then it gets progressively worse if I leave it in park or in gear with idle until it dies. It's commanded to idle at 925 once at operating temp.
I've adjusted the TB set screw and reset the TPS several times.
I have a new fuel filter to try. I have a new Racetronix pump in the car.
I plan to take the IAC out and clean it.
I have a new LS3 MAF/IAT in the car. The MAF is disabled but the IAT is enabled.
I had a check engine light come on before I replaced the MAP and it's gone (will have to see what the log shows on Monday if it is MAP or IAC related).
I also plan to drive it today to see if it stumbles/surges under load in gear to rule out the IAC as being faulty.
Any other ideas for what to check? It was doing it before it was tuned. I mean it surged horribly and would die out quickly - and it had a mail order tune on it where it idled fine for about 5 minutes and then never idled right after that. So it's worked on and off and seems to stop working just because.
After the street tune, it idled and drove fine for about 2 hours during the process. Once we finished it had a high idle hang when I pulled it back into the garage. And since then it's been doing this **** while idling once warm. So it sounds like it developed a vacuum leak somewhere that only shows once warm? Because it idles dead nuts when cold.
Any thoughts?
