gpracer1

A few months ago it started doing this. Come to a stop light and the idle may or may not stumble then recover. I think I remember it happening after I started it when the battery was a little low after sitting for a week. If I very slowly press the gas pedal 2% it will drop to 4-500 and run real rough.....3-4% and it revs up.
I am watching on EFI live scan and all the sensors seem to look normal as in no jumps.
Strangely during idle and the stumble, the O2 sensors are showing full LEAN like a vac leak, but I cant find one. Its drving me mad

Car runs like a raped ape, great mileage.....but poor driveability at idle speeds in parking lots.

Since then I have replaced plugs, sea foamed, replaced O2 sensors, MAF to tbody coupler, cleaned MAF, replaced PCV hoses, checked for Vacuum leaks, cleaned tbody, isolated the purge solenoid, hosed everything with carb cleaner, measured voltage at TPS...smooth, fuel pressure 58-60. Tried several idle relearns, and just reinstalled the tune....handheld tuner. Same deal.

I hope someone has an idea.

memmer

Sorry can't help, but maybe you should try tech.
Fred

Macleod52

Is it possible the TB wasn't thoroughly cleaned? Maybe the plate is still sticking?

c4gone

mine did the same and it was the o2's. just my experience with it

gpracer1

Just installed brand new ones last week.

It's almost like the PCM is bad

Also no codes unless I let it sit idle for 10-20 min making it stumble over and over then I get lean codes both banks. I think P0171 and P0174.

c4gone

could it be bad cats that are making it run lean and throwing the o2 codes?

n8dogg

What mods does the car have?

You're using EFI Live, have you performed a tune to your car? Feel free to post it up and I'll check it over.

Any changes to coolant temp, idle relearn, OL/CL operation?

gpracer1

Just drove it to the bank, 30 seconds into warming up in the garage I could make it do the stumble with light throttle. I assume it was still in closed loop.

Mods are:
Honker air intake
LG streets headers x pipe and high flow cats
ZO6 mufflers
1.8 ratio Yella terra rockers
catch can
Diablo predator tune

Car runs great other than the stumble.
Just ordered a TPS, I think its either that or the MAF....cheaper one first.

I do have one license left for EFI live, but I don't know where to get a real tune. Was hoping a tuner already has a tune for my mods that I could buy the file.

n8dogg

Highly recommend a tune, especially for the rockers. I'm happy to help you with a baseline tune. You'll have to send me the tune file and a 30 minute log file.

gpracer1

I wish it were that easy..... I have a Diablo Predator hand held tune currently.

I also own EFI live for my 99 Tahoe that I did a 0411 swap. It came with 2 licenses, one is used for the Tahoe and the other is still available to go in my vette, but I need a tune with my mods to install.

I guess I would need a tune file from a vette that has near the same mods and then log some runs and go from there?

n8dogg

Run EFI Live/Tune Tool and connect to your car. Read the tune and Save As. Run Scan Tool and select default imperial PIDs, connect to car, data long a good 20 minute drive. Post up or send me both the tune file and log file.

gpracer1

Can I do that if I don't have an EFI live tune on the car?

BTW, I just put a new TPS on it and the same thing

n8dogg

Yes, you can read and save the factory tune.

gpracer1

Ill try it tomorrow.

gpracer1

Temps finally dropped to under 100..... so finally able to get to it. Able to read and save predator tune, restore factory tune, license my pcm with EFI, read and save factory tune, and restore predator tune file in EFI live......so at least it will still run good.

So far new TPS and new MAF and still does it. Will still need to run it around town tomorrow a few times to learn the pcm, then I will log some driving. Do I need to select certain PIDs? or all of them?

Ill try to email you my current factory vs predator tune in case you see something obvious.

Marc

gpracer1

Posting the update. (because I hate when people leave threads hang)

Finally got around to ordering a used throttle body with motor off ebay for $80 and the problem is now solved. I wasn't going to screw with taking the motor off the tbody to see which one it is, but I assume its the motor. It was starting to hang at 1500 rpms sometimes when driving for a while and coming to a light, then it would stumble and idle crappy.
Idles great now and no driveability problems.
After not driving it for 2 months due to getting a 2000 Ford F350 crew cab long bed dually diesel and driving that, the vette feels holy shizzle fast again.

Catman58

Do you have any codes?

gpracer1

Nope.