Hello everyone. This is my first post. I have been reading this forum for over a year and really appreciate all the valuble info that has been posted. I finally registered so here I go. I own a 93 LT1, 40th anniversary with a K&N cold air induction pipe and the rest is stock. I have 120k on the car and have been replacing various worn components since I bought the car in September 2001. When I first got the car it had about 96k and idled like a rock and ran very strong. As I am a middle aged geezer, I ricky raced it a little bit but drive pretty conservitavley. About 6 mo. after I got the car, the idle started "bumping" ever so slightly and got progressivly worse. Then a little while after, I noticed sputtering and backfiring through th exhaust and throttle body upon torque demand. I have never seen any smoke at all. I think I have 2 seperate problems. The sputtering feels like a timing advance and retardation problem. The idle feels like an electrical short as it is very intermittent. Both of these problems are directly related to outside air temperature above 85 deg.F. I have replaced almost everything in the ignition system including Optispark, plugs, plug wires, AIC, MAP, Coil, Coil Modlue, Fuel Injectors, Water Pump, EGR Valve, EGR Sensor. I have also put plastic looms over the plug and coil wires as I read in a thread on this forum. I have a remanufctered ECM and have dismantled it entirely and it looks good. Yesterday I put a new timing chain on thinking of timing chain stretch as I also read in a recent thread. My old chain had about twice the slack of the new one but looked pretty good. I am putting the car back together today but don't expect the chain to fix the problem. The only error code that I ever got was 32 for the EGR. I m thinking about replacing the knock sensors and the O2
sensors but really think I would get an error if they were bad. One interesting thing is that every time I reset the chip, (i.e. disconnect the battery), the car runs 200% better for about 100 miles. Thank heavens I LOVE working on my car and all these replacements are preventative maitainence on my high mile Vette. If anyone has ANY thoughts that I haven't done, I would greatly appreciate any reponse. Sorry this thread is so long, I just had a lot to say. [IMG]

 

Welcome to the forum!!

Have you changed you TPS? Cleaned out your IAC and T/B with carb cleaner? That is where I would start and make sure you set the voltage to the recomended amount..

 

Wow, you just described exactly the problems I have been having with my '86 L98 for the past six months! However, I haven't noticed a connection between temperature and the intermittent fits of poor idle quality. One time when the car was running roughly (spitting sound coming from exhaust) I disconnected the set-timing connector and the car idled silky smooth. I too suspected that the problem was timing, but have also replaced all of the usual supect components of the ignition system to no avail.

After extensive research, troubleshooting and late night shop-manual study sessions, I now suspect that the problem may have something to do with the EGR system, AIR system, faulty ECM, or even a lifter that may intermittently not be working properly, causing a valve to not open or close all of the way.

I'll be watching this post as well for more ideas. Hopefully we can get to the source of these intermittent idle problems. Good luck.

 

Welcome to the forum... :cheers:

I would say that the chain slack might be part of the problem in the car.

You may also want to pull the distributer up out and inspect it for wear, it could be doing a few different things. One it could be walking up the cam gear and then dropping down causing a slight jump in timing, but this will usually cause the distributer to self distruct faily quick. The other is the bushings in the distributer could be shot allowing it to wobble. This is typically mor..........ahhh fudge this is an opti car isn't it....nevermind :crazy:

 

You are describing the exact symptoms that I have had for at least the last 6 months. Are you getting a slight popping in the exhaust at idle? I have replaced a lot of parts too without nailing down the problem. The list is: plugs, plug wires, opti, (coil and coil driver tomorrow morning), EGR, EGR solinoid, MAP, IAT, FPR, injectors serviced by Rich @ Cruzin, both O2 sensors and both knock sensors. And for kicks a new water pump, belt tensioner and belt. I'm begining to think that the problem is in the valve train ie: lifter, spring ,push rod, cam lobe, etc. as there isn't much else to change out top side. It would be great if someone would get to the bottom of this. :confused:


[Modified by ittlfly, 6:48 PM 12/23/2002]

 

Have you done the TPS and IAC adjustment thing?
https://www.corvetteforum.com/techti...D=55&TopicID=2

 

I had a similiar problem on my 86. It turned out to be a cracked vacuum line to the EGR. I am not familiar with opti cars, but is there a charcoal canister or other vacuum device controled by the ECM?

 

Yes, it's controlled by a solenoid at the r/f of the intake. I found a leak (hole) on the bottom of the small "L" shaped hose from the soleniod to the Throttle body. But the problem still exists. :cry BTW, Gm is real proud of THAT hose $5.00+ for a 3" vacuum hose.

 

Wow!! It seems that this problem is widespead. Yes, I have replaced the TPS and removed, cleaned and reset the AIC. I got the car back together yesterday with the new timing chain and started it up. It fired up the first crank and ran like a brand new engine. It was still up on jackstands with the front tires and hood removed so I haven't been able to take it for a spin yet but I have high hopes. Remember I previously stated that every time I "reset " the computer it ran better so as I am optomistic, but I will have to run it a bit to be convinced. I will be sure to post the results as soon as I have accurate info. I am also thinking that I need to get a diagnostic scanner of some kind. I have taken the car to several local garages who supposedly have a scanner of some sort but was dissapointed at the results. For instance, the last garage reported that the scanner indicated an open EGR valve when I had just installed a new one and an EGR solenoid from the dealer a day before! I removed the EGR valve and checked it out manually and it was working fine. I think doing it myself is the way to go. If anyone has any reccomendations and / or links Iwould greatly appreciate any info. Thanx again for all the response.

 

Yes, I think you would be wise to troubleshoot it yourself. I have spent hundreds of dollars at local shops here in Phoenix with no real results. What I find that most shops want to do is put a few turns on the minimum air adjustment screw and maybe check the AIC and TPS and thats about it. You have to wonder sometimes if there are still good qualified people at these shops who know any more than you do! :jester

 

Try the O2s. I have heard that the O2s start to go bad at about 50k miles.

BTW, I have been battling my bad idle and cutout problem for about 3 months now. Mine is all the time though.

 

So, was the chain the culprit Roger?

 

My car has been at the local Vette doctor for two weeks for this problem. They have been busy and haven't tested it yet but I will post the results when I get it back. Like everyone has said, this seems to be a VERY common problem that drives everyone nuts and affects TPI and LT1's.

There has got to be a solution............

 

Tworottiedogs

Please post the results shops answer to the problem and exactly what was the fix. There's a lot of folks around that would like to have the definitive answer.
:confused:

 

I wonder if it could be burnt valves?Have you done a cylinder leak down test?
You might ask why its ok after resetting the computer? And thats a good question.I guess the timings different for a while.I dont know for sure.But I stayed at a Holiday Inn last night.Ha Ha.
Just a guess since you mentioned the high miliage.
Or could valve guides cause that?
I think these cars were hard on valves cause they make them run so hot.
Sorry to add more questions than answers.

Goodluck all. :chevy

 

Well, I finally got the car back together yesterday. Had to shut down a couple of days for the holidays and such. It was the 1st time I had the hood off and it was a little bit challenging to get it re-aligned. Anway. PROBLEM FIXED!!!. The car now idles like a rock and the old head snapping torque is back. The power band is solid thru all the gears and everything feels nice and tight. I'm taking it a little easy for the first 100 miles or so to let everything work it's way back into shape. I must say that I am truly amazed at the difference. As I said earlier, the old chain only had about 3/4" slack. The only thing that I can think of is that when the chain heated up it got a LOT larger due to metal fautige. Having worked in machine shops most of my life, I know that the torsion and tensil values can change a lot under heat and load. I also noticed that the old chain links would lock in at 180 deg. whereas the new chain links would roll back 270 deg. + per design. Maybe GM corrected a design flaw and kept it hush hush? NAW, they would never do that! I did add a wire loom over the primary OPTI wire, not the one that goes to the coil but the other one that is approx. 5 individual 12 or 14 guage wires that runs beside the plenum box. I really think everyone with a high mile Vette should consider replacing the timing chain especially as a new one only costs about $20.00. The only challenging thing was pulling the Dampener yoke. I bought a standard 3 bolt puller with a 10" center bolt that went right over the 2" square cross frame and used nuts and bolts thru the 3 holes in the yoke. I accessed the center bolt from underneath the front of the car. You also have to loosen the oilpan bolts to drop the front of the pan to remove the timing chain cover. It also fixed a shimmy in the steering wheel that I had going 70 mph+ under acceleration. That old chain must have really been slapping around al ot. Anyway, we have clear blue skies out here at about 70 deg. so I think I'll take her out for a run later on. :steering:

 

That's good news Roger, thanks. I'm getting a new chain along with my Dyna-spark which is due the first week in January some time.

So, you only had to loosen a few oil pan bolts to get the front cover off? My FSM states that the entire oil pan needs to be removed...

Jay

 

Yes Jay, I loosened about 4 bolts on each side and the front 2 about 1/4" and the chain cover slipped right out. The chain cover has a female rubber groove that fits in to the oil pan bevel. The oil pan does not trap the chain cover. Hope this helps

 

I am not a certified GM mechanic as the airline I work for made me get cerified with Ford. :cry I started out as a GM mechanic (also imports) and worked so until 1991 where I chose to go on with American Airlines. Respectfully speaking here to defend the 17+ years I have been a mechanic, most problems are different from car to car so what might fix one car may not fix another. Yes we understand how all the components work together but that is exactly it, they work together and to predict what a problem is by laying my hand on the hood like Mrs Cleo won't happen. Also just like a rumor, people describe problems differently and what may seem one way to one may not seem the same to me. In the late 80's GM had finally got a grip on computer controlled fuel injection and was doing a pretty good job of it. I remember using my Snap On Troubleshooter to see drivability problems and I can't believe a nearby dealer will not do this now. If a dealer says they can't find the problem I would never go there again but NOT all dealers are the same so why not take the car somewhere else. I personally can't stand it if I can't figure out what a problem is. To me it is the biggest insult (to myself) in the world to tell someone I can't fix it or I don't know what the problem is when it comes to my profession. I really don't want to tell everyone to change this and change that and spend a ton of money only to find out it was something different and on top of that make myself look stupid for the suggestions. On the oher side I really want to and LIKE helping people and might offer a suggestion of where I would start looking for a problem. This does not guarantee the fix but is only a suggestion and a hope that it might fix the problem. If the problem costs you 250.00 or 300.00 to fix at the dealer, how much are the parts that you have already replaced and your time? Maybe everyone needs to do what my father called "minimize your losses" and take it to a good dealership. I am sure Jeff Kopp's dealership would have found the problem from the way people speak highly of him. If anyone in the Chicago area has a problem that "nobody can fix" please e-mail me and when I have time I sure would like to take a crack at it. I really don't think I will be flodded with people by this statement but if it happens I guess people will have to get in line since I would be doing this to help and not "for the money". The only thing I ask is that it is truely a problem that "nobody can fix" and not a way to get something for free or cheaper as this happens alot to me.

 

Weracemo,
How about a quick trip to sunny Calif? I've had this popping/missing for 6 months and it has been diagnoised from a bad TPS to failure in the muffler bearings. :jester So far nobody has been right.


[Modified by ittlfly, 11:17 AM 12/28/2002]