1G idle jumpy, log included

[sspat]

Hi

My car is a 90 1g dsm turbo awd, freshly rebuilt engine, all works fine except one problem that has not gone away, it was all the way from the day i bought the car.
The engine is a 6 bolt block, 9.0 CR pistons, head all stock, 755cc injectors, walbro 255lph fuel pump, fidanza lightweight flywheel, hks ssqv vent-to-atmosphere bov, ecu+ running with GM MAF 3", GM IAT, GM MAP and an Innovate Motorsports LC-1 wideband, there's more but i guess that's all that could affect my problem.

The problem is - after i stop from on-throttle driving, the idle stars bumping for 15-20 secs in a set range of rpm, then suddenly by itself gets normal. I've spent a lot of time looking at the captures but can't get a clue. I thought maybe you could take a look if i may ask for your time, and give me some advices where to look at. I would be sincerely grateful.

The ECU+ log: http://oghmacg.ru/hh.jpg

 

[dsmgst1996]

Hi

My car is a 90 1g dsm turbo awd, freshly rebuilt engine, all works fine except one problem that has not gone away, it was all the way from the day i bought the car.
The engine is a 6 bolt block, 9.0 CR pistons, head all stock, 755cc injectors, walbro 255lph fuel pump, fidanza lightweight flywheel, hks ssqv vent-to-atmosphere bov, ecu+ running with GM MAF 3", GM IAT, GM MAP and an Innovate Motorsports LC-1 wideband, there's more but i guess that's all that could affect my problem.

The problem is - after i stop from on-throttle driving, the idle stars bumping for 15-20 secs in a set range of rpm, then suddenly by itself gets normal. I've spent a lot of time looking at the captures but can't get a clue. I thought maybe you could take a look if i may ask for your time, and give me some advices where to look at. I would be sincerely grateful.

The ECU+ log: http://oghmacg.ru/hh.jpg

Where do you have your gm maf located on your piping ?

 

[sspat]

Where do you have your gm maf located on your piping ?

Right after the blow-off, some 30cm before a 90 degree bend going into the throttle body.
The strange part i see in my log is that the MAF output frequency during that idle bumping is stable, the ECU+ translated MAF signal is also stable, but the MUT-II air flow is jumpy in that part, so the stock ECU sees as if the actual air flow is changing up and down, but how, if the direct MAF output is stable?

 

[Afizzle]

hope this thread helps

Terry's Talon Troubleshooting Tips #3 - Fast Idle (aka. Idle Surge)

my theory: even if the above link doesnt help it is still imo necessary maintenance

 

[Afizzle]

hope this thread helps

Terry's Talon Troubleshooting Tips #3 - Fast Idle (aka. Idle Surge)

my theory: even if the above link doesnt help it is still imo necessary maintenance

 

[sspat]

hope this thread helps

Terry's Talon Troubleshooting Tips #3 - Fast Idle (aka. Idle Surge)

my theory: even if the above link doesnt help it is still imo necessary maintenance

That's brilliant, thank you very much, gave me a lot of insight into my problem, and the symptoms are absolutely the same and can be clearly seen on my log:

1. O2 sensor registers lean mix
2. ECU adds fuel to achieve correct mix (injector PW goes up)
3. rpm goes up to 1500, ecu cuts fuel, rpms drop
4. at low rpms ecu catches idle again and whole thing repeats

Look very much as a stuck ISC, beacause other things on the list are checked, there are no vac leaks in the line and i got an idle of 1000-1100 with the BISS fully closed. I'll replace the ISC and confirm if that was the problem.

 

[clipto]

Sell gm maf crap and buy link with speed density, gm mafs so inconstant you will be much happier with out it.