redcamaroz28

Ok, first of all, I have read and reread as many threads as I possibly can find about the infamous idle to 2300rpm stumble(what my car has had for the last 2 weeks)....I need an sure solution for this problem fast because this is my daily driver to school, and it is physically impossible for me to fit on a bus (I'm 6'4"), so I need to fix this by sunday.
As other cars, my car does not do this much when it's cold, but when it's warm, i can barely get it up to speed without having to downshift it to get it above 2500rpms, and when it does stumble, hesitate, and buck, it makes a ticking/clanking noise from the front of the car.
The twist of this is, at idle when warm, (at night) the lights will dim, guages and headlights, while the idle is choppy in drive, but when I put it in neutral, it smooths out. While the lights fluctuate from dimming and going to there normal brightness, the voltage meter jumps up and down about 1-2 volts, but always staying above the middle line, and when i put it in neutral, it goes away with the dimming.

So far, I've replace the plugs and wires(2 months ago, checked 3 times in the last week), coil, 60k tune up w/ fuel filter and new egr valve, ran fuel injector cleaner with 93 octane, and today replaced the o2's. The o2's smoothed out the above 3k, but I don't think these are part of my car's problem.

I have narrowed the suspects down to: injectors(friend has extra set), fuel pump, otptispark(which I don't think it is, or I hope it isn't this), ignition module(the thing by the coil), or the alternator/battery(could not be giving the ignition enough spark? and dropping volts?).

I'm trying not to make this like all the other posts, but I've had too many opinions about this, and not enough money (I'm only 16) to try to fix all of these. Also, I haven't found a post yet on both voltage dropping on the guage and a stumble, so could it be I have 2 problems?

If anyone has had this happen before, please post your experience or opinion to what this could be.
I'll be happy with even MORE possibilities, because as of now I think I have heard almost all of them.

Thanks
Ryan

96cam4ro

Since your headlights flicker, I don't think it's fuel related. Most probably it's your Optispark. My car had a stumble at 3500 rpms - a new opti fixed it. Usually when your ignition module goes bad, your car starts, then dies immediately..

redcamaroz28

I forgot to mention, when warm and in reverse, it feels as if the the car wants to hop. It bucks around alot.
Also, could this be a clogged cat.
96cam4ro: Thanks for replying, but what I don't understand is how the headlights would be affected by the opti, cause if the engine stays running, shouldn't the lights stay at their usual brightness(just like when reving it, they stay the same)? And how would an opti have anything to do with the volt gauge going up and down only at idle?
I'm not trying to deny your statement, I'm just trying to learn about our cars (once again, I'm only 16), so I do want to learn more about our cars, even though there are some crappy designs--such as lack of space
Why did they make it so that we need about 2 feet of extensions to get to our o2's.

Ryan

MZK4252

That sounds a lot like the prob that I've been having...I haven't noticed the flickering or the voltage change though. I just changed my opti and that was NOT it...dang.

I would check for bad grounds...I think that might do it.

Best of luck to ya...

87IROC-Zowner

I'm a Third-Gen guy all around... but the last two Fourth-Gen Camaro's I've looked at have had the exact same problem that I noticed right off. The battery was an aftermarket in both cars and both were loose. Being that these cars have a much tighter engine compartment, the positive side of the battery had arched numerous times against the A/C line coming from the condensor on both cars. Might check this problem on yours as well. If the little battery hold-down is missing on your car, at least put a bungy strap to hold the battery in place.

Was also just working on a '94 Z last night which has a slight hesistation from idle-2000 RPM's. There is no bucking/missing/coughing, just seems like a dead spot in the RPM band. We installed new 8mm wires on it, but it was raining and wasn't able to test the results. Hopefully this weekend he'll be able to get it out.

badass383

You might want to check the EGR by disconn. and plug the line and take it for a ride.

As far as the main thread, I had 2 vehicles do this same thing although not bot GM. One was the idle solenoid in a F@#$ (sorry guys) causing the idle to go too low and alternator would then put out to little. This would cause the computer to go like a brown out. Started acting wacky with lights and all that. The other was a GM and it turned out to be a bad alternator doing the same thing. To low voltage out and system goes wacky because it was below the threshold for proper operation.

Question? What is the battery voltage when the car is acting funky. That is what do you measure across the battery when it's doing this?

could tell yoy alot

magius231

can't confirm this, but one of the people I talked to at a GM dealership said that sometimes the EGR passage in the intake manifold leading to the EGR valve gets plugged up with carbon and you get the same symptoms as a bad EGR valve. Again I can't confirm that.

Gripenfelter

Does your oil pressure hop around when the car is warm??

It could be something serious.

My car did that when I spun a main bearing.

But unplug your MAF and see if your car does it in open loop when the car is warm.

If it does, its not a sensor problem.

JSK333

The voltage dropping sounds like a side issue due to the bad idling.

Have you replaced the EGR solenoid too, or just the valve? Try the solenoid too, the black thing on the driver's side of the intake manifold toward the back.

Since it stops around 2300 RPM, it sounds EGR-related--the stock PCM tune has the EGR operating from 900-2100 RPM.

mobleman

I think you have two separate problems

Light flickering: I had the same thing last year plus very low voltages. Replaced the alternator and the problem immediately went away.

Hesitation: I posted this a week or two ago, maybe it will help,

Quote

"Long story behind that question. It was the classic low rpm hesitation, car works fine when first started, but once it was warmed up and in closed loop it would hesitate or bog at aroung 2000 rpm. I spent a 1 1/2 years chasing the problem and even logged diacom data to see if I could find any trends. I could actually see the hesitation onth e data plots!!
This topic has been discussed at length on this board, but I'll give you my take on it.
Things I tried and or checked:

tp sensor
maf sensor
o2 sensors
replaced knock module with lt4 module
checked and changed wires
checked fuel pressure
checked egr operation
pcv valve
thourougly cleaned the throttle body
checked the canister purge system by temporarily disabling it
checked and cleaned injectors


All of those changes didn't make much of a difference, although the lt4 knock module removed much of the false knock I was getting.

I believe the key to the problem is that the hesitation only occurred once the car was warmed up which means all systems are at operating temperature and the ECM is operating in closed loop. I decided to test a theory by forcing the car to run open loop while warm (simply run the car with the maf sensor unplugged). I could notice a difference, the problem was still there somewhat but it had improved. So I replaced the optispark.
Whamo, Car is running better, not 100% but definitely better.

Next came the biggest improvement. I installed mac headers and an off road pipe hooked up to my flowmaster catback. Car ran like a top!! I'm thinking, "Wow, that’s one of the best bolt ons for the money!!”
Turns out that wasn't the only reason for my power gains.
The next weekend, just out of sheer boredom, I decided to cut the catalytic converter off of the stock y-pipe. What I found convinced me that the hesitation could be one of or a combination of, two problems. The cat was severely melted on the inlet side, there were air passages, but flow was severely limited.

Hang in there, I'm long winded but here's the summary:
My theory on the cause of the hesitation problem:

First the coil wire. Way back when the car was one year old, I had a corroded coil wire which caused the car to stall and not start whenever it rained and I had run threw some small puddles. While trying to restart the car it would start hard, backfire, stumble etc and then die again. Eventually the car would start. This I believe caused a specific chain of events:
a) The hard starting backfiring and stumbling damaged the optispark.
b) The hard starting caused unburnt fuel to enter the exhaust and partially poison the cat, causing the front portion of the brick to melt slightly. I had checked the cat externally before (glowing the smell of rotten eggs etc. but could find no indications (externally) that the cat was damaged.

I believe that the problem occurred once the car was warmed up and the ECM was in closed loop, exacerbating the optispark problem. Additionally once the cat was at operating temperature it further restricted exhaust flow.

That’s my take on it. Feel free to email me if you have any questions. Hope this helps!!!

guest

when you unhook the MAF sensor and the car goes into closed loop, does it take information from any of the sensors then, or does it just go with preprogrammed information. i was just curious because i have the stumbling problem and have driven around with the MAF, 02's, MAP unhooked and it didn't help anything.

mobleman

unhooking the MAF will put you into open loop and runs in speed density mode. Since it cannot tell what the airflow into the engine is anymore, it uses a set of default tables to run the engine.

JSK333

Unplugging the MAF sensor won't put you into open loop, it only defaults to speed density mode.

SD uses preset Volumetric Efficiency (VE) tables, along with the temperature of the incoming air (IAT), to determine the density of the air. It will still operate in closed loop, allowing the O2 sensors to correct the AFR.

This might even be something as simple as needing to clean the IAC out, which regulates the idle.

RicocheT

I also have had a stumble when i cruise around in 6th gear at very low rpms.. Car bucks and stumbles at very light touch of the throttle.. Started after I installed my headers.. I tried changing the usual... plugs, wires, o2 sensors. And have no gotten the stumble out.. I stopped looking for it as of now b/c even when i scanned it all the varibles looked ok so i figured it wasn't much of a problem. More annoying than anything and the car still ran alright at the track.
Reading through the posts lately though I think i may try unplugging the egr to see if that helps, if not then I guess it's going to have to just stay that way

Kreinmc

You know you can fit on the bus.