GR8WHTZ

Ok, I bought my '95z m6 about 10,000 miles ago (now at 80,000mi). Since day one the idle has been slightly rough. I've been slowly trying to track down the problem, but am running out of ideas. I know eveyone is going to say it's the OPTI, but i'm pretty sure it's ok, as I don't have any high rpm misses or drivability issues... It just really annoys me at this point.

Symptoms:
1) Rough Idle
2) Popping in exhaust when deaccelerating
3)Running rich - BLMs run @ ~120-124 for both banks, carbon on rear bumper
4) Sometimes slow to start when sitting overnight (3-4 cranks)



I have checked/replaced
Plugs
wires
egr
AIR
IAC
Vacuum leaks
Injectors- measure 12.5-12.8 resistance
All sensor readings normal (except BLM's)

I really don't think it is ignition related because the car doesn't "cut out" under high load/ high rpm. Also I'm pointed away from the OPTI because the symptoms have been the same for so long. Most of what I read says when the OPTI goes, it deteriorates quickly.

I'm going to check fuel pressure next, and I have a couple slightly noisy lifters, so I might do a valve lash adjustment soon.

Anyone have any ideas?

Thanks,
Dave

Finchinater

Check the IAC. That was my problem. The pintle gets gunked up with carbon and you might want to clean it or if you can scan it, check the counts on it. Can't tell you the specs for normal idle and heavy load. It can cause your car to suffocate and cause you to idle badly. Think it's around $90 and and easy install.

Hope this helps.

Finch

GR8WHTZ

IAC Counts are OK, and I did take it out and clean it...

thanks

ShawnMacAnanny

My car has the exact same symptoms. Do you by chance have a Jet module? I was just wondering becuase they mess with the A/F. Have you ever noticed a loud POP, completely random when you try to accelerate? Sounds like it's almost from the intake. I'm gonna go remove the IAC (if i even can) and clean it with some electronic cleaner to see if that helps.

ShawnMacAnanny

Nevermind no I'm not lol.

GR8WHTZ

Anyone else have any ideas? It's gonna have to go to the shop(4 ltr. word)

Dave

doodad

I am pretty much in the same boat, please keep me posted.

RealQuick

What are your 02 mV look like at part throttle and WOT? Can you log runs with freescan?

speedcrazy

myself i would check the fuel pressure for sure while its running and when you turn it off. you said it cranks alot before it starts if it sits overnight so it could be loosing pressure as it sits. if it is loosing pressure maybe a leaky injector or something wrong with fuel pump.

GR8WHTZ

Ok, I purchased a fuel pressure gauge today. Before startup(key on) i get 41-42psi. @ Idle I get 34-35psi. I see a 4-6psi pressure DROP after 30mins... and a 20psi drop after 1.5hrs...

SO... It is probably a leaky injector, or pressure regulator, right?
What about the gas cap?


Any other ideas from you guys?

Dave

gamecockfan04

This is a symptom that probably 99 out of 100 LT1 owners experience and Ive replaced everything you have and to no avail. The only other thing I can think of is a coil(I tried and it didnt do anything), or the Ignition module. A shaky Idle is normally Ignition related, or Air / Fuel related and it looks as though your fuel pressure is fine. The only other suggestion would be to carefully examine your intake elbow. If its gashed, or torn it will cause backfiring, idle, sluggish problems. I had a torn one and a 1Le elbow fixed that, but it still has the shaky idle. Ive been trying to find my problem and finally have just learned to live with it, but maybe one day I'll solve it.

gamecockfan04

That little of a drop in pressure after 30 minutes is not a big deal. Its going to slowly drop, so I wouldnt worry about that.

Grebas94Z28

If you have the time, skill, and patience to do it, remove the opti. Just to take a look at it. Take it off the car, especially inspect inside and the bearing, make sure it spins freely. My car has about 80k and I just replaced it. I have another post here http://web.camaross.com/forums/showthread.php?t=302929

At most the only thing you have to lose if you can do good work, is replacing a couple gaskets for the water pump and some time if it doesn't turn out to be bad. If you find out this is your problem then you have solved it. and spent a lot of money on a stupid opti-crap!!

doodad

That is what I just found out. Damn opti crap cap is arcing or something. Time to do it again.