The LT1 That Could

iTrader: (3)

It's back again. this thread comes up so often, I hate to do this, but I'm looking for some advice. The car is having a low RPM stumble, not so much of a miss, but stumble and hesitation to accelerate. Under constant throttle (cruise) there is a small noticeable miss, but the main problem is accelerating from a stop. The car will spit and sputter and act like it wants to die when stopped in gear at idle. A quick rev and the problem isn't apparent, until you accelerate again. this has been going on for a while, and here's the history of my most recent problems...

water pump went out and was leaking thru weephole. didn't replace opti, car ran fine after this....

heater hose got cut and was spraying back onto plug wires, car ran like crap, fixed hose, car ran fine...

now its doing it again. It only does this after being driven around for 10 minutes or so....once it happens it doesn't go away until the car has set for a long time.

Soooo, do we think its the opti, or should I just try some regular maintenance. Plugs are less than a year old, as are the wires...no wires rubbing header. Stock fuel system, thinking it may be a filter, but i doubt it.

anyways, any and all suggestions are much appreciated. This car is not going back to the shop, I am fixing this problem myself bcuz I'm tired of dropping money at a "performance" shop, to only have the car run good at WOT...which it does fine with, only under partial throttle or idle do i have probs. even from a dead stop if you hammer it, its fine....however it will stumble if i try to get up on the converter, but as soon as you nail it...she clears out....WTF!

infinitebird

iTrader: (11)

I'm going to suggest O2 sensors because what you describe is exactly the symptoms of bad o2 sensors. If you have a scan tool you can easily check whether the o2s are working correctly.

runs good at startup - 10 min -> O2s don't operate at cold temp
runs bad at idle/part throttle -> O2s operate at part throttle/operating temp
runs good at wot/high rpm -> O2s do not operate at WOT

The reason it doesn't go away until the car sits for a long time is because until it cools back down again it will start up and go into closed loop almost immediately. The reason accelerating from idle is bad is because when you first enter wot, if the computer was dumping in more fuel than it calculated was needed it will use that calculation for wot rather than the standard one. In this way the O2s can have an indirect effect on wot performance.

The LT1 That Could

iTrader: (3)

totally overlooked 02s

sadly, the car has had an code for ever for the AIR system being removed and not being disabled in the computer...A scan would prolly net me some better insight. Ill try and get one next week.

daniel6718

iTrader: (36)

ve never had a code on an obd1 car for air pump as long as theres a fuyse in it...egr will though...my low rpm stumble was fixed by remote mounting my coil off the motor watch it at night every car ive ever looked at has arced to the head...because of the dumb metal bracket they use....

donkey mule

Mine did that when the o2 sensors were going out. It got worse and then I changed them out.

The LT1 That Could

iTrader: (3)

It's throwing code 29 - Secondary Air Injection (AIR) pump circuit. I'll check the coil, but I haven't had problems with it in the past. I am blaming opti or 02s at this point.

LT1MAN

iTrader: (6)

i 2nd the o2's. im having a low rpm stumble right now because i have the new motor and no tune yet. running so rich the o2s have no idea what the hell is going on. so every now and then, under various weather/traffic conditions, cruising at low rpm, it will just barely bump/studder a little. i almost cant notice it under all the new vibrations from the motor, but its there, and im pretty sure its because of the o2's being drenched with unburnt fuel.

A-man930

iTrader: (2)

interesting... I'm still at the point where I need to change the plugs and wires, and I actually just had the coil off the car but didn't space it out I'm having a hard time pinpointing what exactly is hapening since its an m6, but after having it for a while now I'm pretty sure there's some kind of miss/stumble under aggresive acceleration. If I let the clutch out even semi-quickly while giving it any more than 1700 or so, it falls on its face, recovers quickly, and slips the clutch or fries the tires... Also when at low rpms in 2nd or 3rd I'll feel a few lurches when I hit the gas... it's slightly annoying.

396Z28

iTrader: (2)

I to am having the same problem. But its driving me insane cause mine does it even worse when its cold.

The LT1 That Could

iTrader: (3)

Well I finally had some time to narrow down the prob, and it is more than likely 02s, so thanks for the suggestions whoever said that. i let the car idle and warm up in the garage, and as soon as it went into closed loop, or whichever loop it is when 02s start taking readings, the SES light came on and almost instantly the car began stumbling. It sounds more like its flooding the car, and any kind of throttle other than WOT produces a bogging effect, especially when in gear and getting on the converter, it damn near kills the car.

Anyways, thanks again for the 02 suggestions, and does anyone know what size wrench it is to remove those....isn't it a 19mm??

porksoda

iTrader: (39)

I think its 7/8's or 22mm either or will work

A-man930

iTrader: (2)

Wow, sounds familiar (except for the whole converter part), only I don't get an SES. If the O2s are the culprit, will they always throw a code? And now that I think about it, I have gotten an SES code for a random misfire... Now that makes it sound like the problem is with the coil arcing to the head, I would I be able to see it if the motor isn't under load??

The LT1 That Could

iTrader: (3)

UPDATE!!

Finally got around to fixing the ol hefer! Wow, what a difference 02s make! haha

Maybe this will be useful to some one in the future if they are smart enough to use the search function...just wanted to make a quick update that 02s were the culprit of this prob.

Thanks to everyone who recommended that for me!

goodrich969

iTrader: (9)

What brand did you go with?

porksoda

iTrader: (39)

Always stay with Delco. Very few people run Bosch or other brands with no problems but everyone else has nothing but bad things to say about them. Search too, there was a thread asking this same question a few months ago.

The LT1 That Could

iTrader: (3)

Went with Bosch....gonna try them out and see how it goes. The stockers were Bosch and they lasted until now apparently....128K miles!

goodrich969

iTrader: (9)

Yeah, I have bosch but I think I have the same problem.

A-man930

iTrader: (2)

Don't mean to hijack, but I fugured I should ask here before I started a thread.
Question: What part of the coil setup is usually the culprit when it arcs? I was thinking about spacing the ICM/coil out with washers and mounting a piece of ABS plastic to create a barier between the coil and head (maintaining the ground of course). Picture what I'm getting at? I'd rather not re-locate the coil entirely, and this would be cheap... Does this sound like it would help?