AZBlackC4

Hey all. I'm new to this forum, although I've checked out the posts now and then to trouble shoot my problem.
Here's the problem. When stopped at idle, my engine stumbles, misses and surges erradically from about 600 RPM to 1200 or so after I've driven it for awhile and it's warmed up. The oil temp usually reads about 195 or so and the water temp is usually about 210 or so. The surging is so bad sometimes that I have to put my foot on the brake pretty hard to keep it from moving forward, but it doesn't do it that bad all the time! It sounds like I'm challenging the guy next to me at a light, the way it revs up and surges. After I take off, it takes off pretty well and the problem seems to disappear. It occasionally coughs or misses slightly when giving it full throttle, but usually it's pretty smooth.
I've had the spark plugs and wires changed, cleaned the MAF sensor, cleaned the IAC valve, replaced the fuel filter and checked and cleaned the PCV valve, checked for vacuum leaks and it still does it. There was no "check engine light" and there still isn't. My mechanics told me they did not find any codes for the o2 sensors or anything else not funcitioning.
I've scoured the internet and have seen other people with similar problems but no solid identifiable reason or solution for why this happens. Some people have replaced the EGR valve, found vacuum leaks, replaced the fuel pressure regulator, or replaced the O2 sensors, etc, but I don't want to just start replacing parts without knowing what is actually causing this. Why does this happen!??
It's driving me nuts! Help!!

Overboost

opti, opti, OPTI SPARK

AZBlackC4

Opti spark? It doesn't do it when it's cold though. Wouldn't it do it all the time if it was spark related?

Overboost

nope, when my opti went, it ran perfect cold, and would not run once it got hot, it would surge, jerk and sputter once you attained a cruising speed, whether it was 45 or 70

the opti will do many strange things, but most of the time, if it is anything ignition related, the opti is the #1 cause, and I spent alot of cash replacing everything around it hoping it was not it
but it was, once fixed it ran like a brand new car

AZBlackC4

Well, the difference with my symptoms is that it does run well at cruising speed and it accelerates strongly with just a very occasional cough at full throttle at 5600 to 6000 rpm. Other than that, it runs well while driving. It's only when I come to a stop light and it's idling. It can be in gear or out of gear, it still idles irradically, stumbles, and if in gear; it surges.

Thanks alot for the info on your history Overboost, I appreciate it. God, I hope it's not the optispark!! I don't have the cash to replace THAT at the moment!!

Anybody else have any opinions, or have had this happen?? The car has about 86,000 miles on it and in good shape otherwise.

Phat98

Park it in the garage, turn off the lights, pull the fuse for the hood lights, and look for any blue sparks around the Opti, plug wires, and spark plugs. I had a similar problem on my '94 LT1 - I had changed the spark plugs and had a slight stumble off-idle, and you could feel it while idling but pulled great...no codes, no Check Engine Light. I was thinking wires/Opti also.

After a week of troubleshooting I discovered I had cracked the #7 spark plug while installing it - that spark to the block was a sight to behold! Replaced the plug and all was well...

AZBlackC4

I'll try that and get back with the results. No matter what the cause is, I will return when I find the solution to explain it.

Thanks guys!

93Rubie

Lets not forget about the Ignition Control Module on the pass. side head. Before we go and play the "blame the Opti-Spark for everything" game.

Those have been known to give troubles from time to time.

Sounds like some of you learned the hard way that throwing parts ($$$) is NEVER the solution. Diagnostics IS, cheaper too if you have your FSM handy and a few decent tools.

AZBlackC4

Thanks 93Riubie, I'll keep that in mind too. I did a quick look at the plugs and wires last night, and it looks like Phat98 may be right. Even though I had the plugs and wires replaced about 3 months ago, and it cost me a **** pile of money to have them all changed, I did see some pretty good flashing from a couple of plugs! I'll check them out today to see if that clears it up. I'm not much of a mechanic and don't have much to speak of for tools, but I think I can at least check to see if the plugs are tight and the wires are plugged in tightly.

How to you know when a plug is cracked?

AZBlackC4

You're a genius Phat98! One of the plug wires had completely come loose from a spark plug on the passenger side of the car, and one plug at the back of the engine on the drivers side has a pretty good spark coming out of the boot that sparks towards the engine block. The boot that was loose apparantly had been on the plug far enough to run well at speed, but caused a very rough idle along with the other plug thats sparking. I think the loose boot finally came almost all the way off the plug yesterday when the car started to miss almost all the time while driving and surged like crazy when it was idleing. It was pretty bad.
I plugged the boot of the loose plug wire back onto the spark plug and hand checked the boot connection on the sparking boot on the drivers side plug, and ran most of the day today without the surging or missing at all. I still have a stumble at idle that I'm pretty sure is due to the remaining sparking wire boot on the drivers side plug, at the back of the engine. It appears to be on the plug sufficiently, but something is obviously wrong wtih either the boot connection or the plug, to cause the sparking (arcing?).
In any event, the irradic idle and surging is gone and the car runs well 95% of the time. I only have a slight stumble at idle now.
I learned a lesson here; Even though I had just had the spark plugs and wires replaced about 3 months ago, I should not have assumed they were all put in correctly or that nothing was wrong with them. I hadn't even thought to check the plugs and wires thinking they had to be fine. Live and learn.

Thanks alot guys!!

BTW; Are there special spark plug wrenches or sockets to get at these plugs? I have no idea how you'd get at these without nearly taking the engine out! I'll let you know how the car runs after I have the sparking boot or plug looked at and replaced. If it runs like a champ and the slight stumble is gone, then I'll know for sure that it was a plug/wire connection that was causing the irradic idle and surging problem

Phat98

Been there, done that. You may still have a boot not fully on one of the plugs, still causing your stumble. You need to make sure all the boots are securely attached to the plugs - you should feel the 'click' when the boots are pushed onto the plug. I know it's tricky, especially the 2 back ones on the passenger side (#6 and #8 plugs). Also, check the plug wires and make sure none of them are drooping toward the exhaust manifolds - try to move them out of the way if possible. Any plug wires draping over/around any engine metal I like to slip a piece of plastic wire loom (over the wire) to keep it from chafing.

Sounds like you've got a handle on it, good job!

BTW, a small squirt bottle of water also helps to locate those pesky sparks!

93Rubie

Nice job!! I'll take credit for calling it NOT being an Opti-Spark.
I'd would ALWAYS test and verify all ignition components and go to the Opti-Spark last. That way you are sure before you pull the trigger on an expensive item.

Do a search lots of threads on spark plug replacement. Lots of extensions and swivels are helpful. Patience too...

AZBlackC4

Well...I drove the car for awhile without doiing anything more to it, and the symptoms partially came back after it got hot. I inspected the remaining sparking plug,( #7 at the back of the engine on the drivers side) and it was sparking pretty well even in the day light. I removed the plug and it was cracked on both sides of the ceramic. Nasty. Replaced it, and the car runs very well most of the time. It seems that after it gets hot and I've driven it for awhile, the idle rises and drops occasionally and there is still a slight miss or stumble while idling and the dash lights drop for a split second when it stumbles. It surged a little bit too the other day after it had been driven for awhile. Yesterday I drove it for awhile, it got over 200 degrees and it idled almost perfectly. It seems there is still something causing the engine to surge or idle a bit erradically even after inspecting the plug wires and replacing a cracked plug. Do you think this symptom could be associated with the ICM? It still may be the Opti-spark ultimately. The car does have about 89,000 miles on it. At least it does run a hell of alot better than it did! Although the remaining slight surge and idle problem worries me.

Phat98

Yep, the same thing I did...I remember the spark plug socket getting stuck in there and I kinda' manhandled it too much to get it out. Two perfect cracks in the insulator!

I haven't had to deal with the ICM on either of my cars, but I would think it would get worse as it heated up. Have you checked/double checked all your vacuum lines? The ones around the battery seem to go first. If you can grab a vacuum hose and get your hands black, that hose is shot.

AZBlackC4

Thanks for the info. I'll check the vacuum lines again. What is the large black round vacuum device that has hoses coming out of it just above the battery? I know these lines are old. what does this thing do and where do the lines go? If these lines are leaking, would it cause a problem when it gets hot? (I know, I'm pretty needy)

Phat98

That's the cruise control servo...there's a couple of lines to/from there, one runs through the firewall to the clutch pedal - you'll have fun changing that one. Sorry.

Have you tried the cruise and see if it works? A pretty good indicator of vacuum issues (sometimes). You might also want to check the vacuum ball (driver side, inside fender in front of tire) - the nipple was broken off on the wife's car when we got it.

AZBlackC4

Don't have a clutch; Automatic. I'll check the lines again and check the cruise control. I used it a couple of months ago and it worked, but you never know.
I don't know. I drove it today and it ran pretty well. Got up to temperature and after awhile it started to surge a bit and stumble when idling. It also seemed to run a bit sluggish. Like something was restricting the power, acceleration a bit. I replaced the fuel filter when the plugs and wires were replaced so I wouldn't think it would be the fuel. Have you ever used a fuel system cleaner?

Not quite sure where to go from here. Can't really look at changing more parts until I can get more cash, so I'll have to run the car the way it is for awhile unless something jumps out at me.

Thanks alot for the advice and info, I really appreciate it.

Take care!

S'vette

take it back to the shop that did the work and make them fix it, should have a warranty on it if only 3 months old.

AZBlackC4

I've been busy analyzing and replacing parts since I last posted, and I think I found the crux of the problem with the engine idle surging and stumbling when hot.

I first replaced the MAP sensor after reading about a miss and stumble related to this. It was easy to replace and doesn't cost much. After replacement, the engine ran about the same. This wasn't the main cause of my problem. I then decided to replace both the o2 sensors. After replacement, the car ran much better, but still surged and stumbled when hot. I then replaced the fuel pressure regulator after reading about someone who replaced this and their stumble went away. Mine did not. The car ran fairly well, but still had a problem when hot, and in fact, was running very hot and not cooling off well at all. Since my main problem was, or seemed to be caused by heat, I started to look at everything that was temperature related. I took the car in to have the coolant flushed and it ran better right off the bat! It actually seemed to start running stronger after I drove it a little while and definitely ran cooler. I realized I may be on to something here, and replaced the Engine Coolant Temperature sensor that controls the PCM. After I replaced that, the car started to run even better, but still had a stumble after getting hot, and still did not run "strong". The surge at idle seemed to be disappearing, but it still stumbled after getting hot. I noticed that after the car sat awhile after driving, and in the sun, it would noticeably stumble and miss right when I started it until I drove it, and it would start to clear up. I then replaced the Intake Air Sensor, and VOILA! the engine instantly ran stronger, smoother and idled perfectly steady. I've been driving it for a couple of weeks now after replacing the IAT, and have not had a stumble or surge yet. It even runs cooler.
I think I've solved the surge and stumble at idle, but realized that my car is 18 years old and I think all of these sensors, EGR valve, ICM, coil, MAF sensor, etc, should be replaced anyway, even if they haven't completely failed yet.
I'm going to continue to replace the parts that I can, and have the Opti replaced at a shop probably.
I'm excited about how strong this car CAN run when it's running the way it should!

Thanks for everybody's input!!

Phat98

Congrats! Hopefully your aggravation will help someone else down the line...