beltrunner

I've read hours of posts on similar problems of intermittent stalling, and actually went through it with this car about 5 years ago. My '93 LT1 automatic,stocker(100,000 miles) would falter and die once in a while, until it finally died and had to be towed home.Turned out to be the opti spark, which I replaced (I did use an aftermarket one). It was fine for awhile, then stalled & towed again, and it was the ignition module. Replaced that and been good for 5 years.Now it has a very sporadic problem of idling too slow & rough (about 500 rpm) once a week or so. 3 times this slow idle lead to a complete stall. It will start up again, then stall immediately, and start back up and be fine for another week or so. When it dies, all the dash warning lights come on as when you first turn on the key on a normal start. It has only done this 3 times in the past month. I cannot replicate the problem. It throws no codes. Fuel pressure specs are all good. Readings at the ICM are good. The car has original fuel pump, and O2 sensor and ignition switch. When it runs normal it runs great. My question is would a bad opti be this intermittent?Last one killed the the car completely.I drive the car continually and this is such an infrequent problem that I can't figure it out. I'm putting in another fuel pump because I have one on hand, but I don't think that is the problem. Should I suspect the opti? Thanks for any help.

Injuneer

Did you check the fuel pressure?

500 RPM for an automatic is not that far below stock programming (550 RPM in drive).

Check for a sticking EGR valve.

Since it appears the vehicle may be losing switched ignition power (dash lights up like you just turned the key to "run"), check for burned contacts at the harness connector on the ignition switch. That seems to be a more frequent problem as these cars age.

If the problem was due to a problem with the cam position sensor in the Opti, you should be getting DTC 16 and/or DTC 36 when you check for codes.

beltrunner

Thanks for the reply Injuneer...actually this car in now being driven by my daughter, so that's why I am more concerned about it...if I can't make it right, mom insists I sell the car and get something "dependable" for our kid...I had a new fuel pump on hand which I installed this weekend (boy, that was fun)...car runs great with the new pump, but it ran great before the new pump except when it stalled & died...fuel pressure was within specs with the old pump, and the same with the new one...only difference is that the new pump is almost silent compared to the whine of the old pump...the car had just recently passed Calif smog before the stalling problem rose again...the EGR was replaced 2 years ago when it failed smog due to a bad EGR valve...I'm only guessing that these valves are supposed to let you pull vacuum on them when the engine is off, but not hold vacuum when the motor is running? The original EGR would not hold vacuum at all & failed smog, and the replacement EGR passed smog easily...when I manually open the new valve with engine on it can kill the motor, but does release in time when I let go of it...can I replace the ignition switch without pulling the steering column? Thanks for helping save my car from the chopping block.

Injuneer

My first comments were just some possible causes of the stalling that came to mind when I read your description.

The valve is opened by vacuum. There's an air bleed hole through the diaphragm. When vacuum is removed from the valve, it should close. Doesn't matter whether the engine is running or not.

Note that EGR is not used at idle, not above 3,500 RPM, nor at wide open throttle. Manually opening the valve at idle by pushing on the diaphragm should not introduce any vacuum, since the air present above the diaphragm should not be able to flow backwards through the EGR vacuum solenoid, so it should close as soon as you take your had off the diaphragm. I guess the fact it is a negative (exhaust) back-pressure valve may mean it closes faster when the engine is running. Never really thought about it.

If there is carbon buildup around the pintle, or in the hole in the manifold that the pintle block, may be an intermittent leak. A sticky EGR vacuum solenoid could cause intermittent problems, allowing vacuum to be applied to the EGR valve when it isn't supposed to be.

Shoebox has a guide to replacing the ignition switch:

4th Gen F-body Ignition Switch Replacement

beltrunner

So the EGR circuit checks out okay. I'm driving the car for awhile instead of my daughter. Car's been fine until last night, when at about 25 mph it "hicupped" on me...it didn't die, but only faltered for a second...lost power for an instant and then was fine. After it did this the "ABS INOP" light began to flash. I turned the ignition to off, restarted it, and this warning light went on & off as normal. I thinking of dropping the column to check the ignition switch connecters for signs of heat. Would a failing ignition switch cause these intermittent problems? Thanks again for help on this.

beltrunner

Well, so I installed a new ignition switch.There were no obvious signs the old one was bad...but too much work to just put the old one back. The old switch did have one of its lugs discolored,but a meter check failed to find a problem.All was fine for 3 days of driving...but this morning I drove to the store.When I came back to the car it started right up...I put it into gear and pulled about 3 feet forward and the thing died. 3 quick restart attempts cranked motor, but it would not catch. Sat there for 2 minutes and it started up and ran great...The Security light did not flash, but what about this VAT module that can be replaced with a dummy one. Could this be my problem? I've gotta sell my car if I can't fix it.Thanks for any more help to save my car!

GaryDoug

I would check the fusible links on the terminal post near the battery. Try moving the wires around while the engine runs. One could be intermittent. The one of most interest is fusible link E (rust color).