Mechanic stumped

Well, it's been probably a month now since my car started stalling. So far I know for sure that the icm and crank pos. sensor have been replaced, fuel filter is new and there are no diagnostic codes. My dad's code reader couldn't get anything, but the mechanic's said everything was ok. The catalytic converter has been replaced. I do have an aftermarket cold air intake and I run 10w-30 Pennzoil High Mileage mixed with one quart of Lucas Oil. It's filtered through a FRAM Tough Guard. My plugs are Autolite XP and the wires are Delco. I did replace a coil pack a year ago or so, I thought that was my problem, but it turned out to be a fuel injector. So I'm sure I've had at least one of those replaced, I don't remember for sure.

The car will drive fine usually for around an hour, but then if I decide that I want to stop and eat or something then leave it tends to not be happy any more and will run for a little bit, then stall. It's very intermittent, sometimes it's quick and sometimes it won't do it at all. In fact until this last time the mechanic never saw it. If I sit and rev the engine at night or something after it starts with me, it won't want to start the next day. Weirdest thing was I'd come home and pull up in the driveway and it wouldn't die sometimes. Like I said it's weird as hell. And since the mechanic and I both haven't figured this one out, I was wondering if anyone had anything similar happen and what it could be?

The mechanic figures that if it'll finally completely die, he'll be able to find it, but until then, I'm going to be the one taking the risk, driving around trying to make it die and not freeze outside.

First of all what year is this car, lots of stuff in the post but the required info, second when it won't start you must check for fuel pressure and spark, no other way, this is basic diagnostics. Or check it with a scanner and see if there are cranking rpms during the no start event.

Sorry, it's a 94. The mechanic tested out the most obvious stuff. Fuel pump, filter all that jazz. It cranks, but every so often it just doesn't want to start. But only after I mess with it. But otherwise it'll start fine. Of course winter weather doesn't help much either. Like I said it's all been tested and quite a bit replaced. I don't know everything that the mechanic did to it since I wasn't there when he worked on it.

I think I forgot to mention that the car has been better recently after being in the shop. Now, so far anyways, it'll kind of restart while I'm driving. No particular speed or anything. Just at some point it'll basically hiccup, everything dies out and comes right back on. The lights do stay on and the dummy lights will come on. Then the car starts running again, like I turned it back on, but it kind of turns itself back on. The whole time I never touch the key. After that it runs just fine again.

I've had intermittent problems in the past as a result of contaminated fuel or accumulations of "stuff" in the tank that block up the strainer to the fuel pump. In my case, I think repeatedly parking on a sideways incline allowed water to run into the tank through a vent hole around the gas gap or something.

I've checked a few things, last night I checked around my gas cap, since I've bought a keyed gas cap. My parents used to have problems with people stealing gas out of their boats and that's where I parked my car. It looked like it should seal up fine. I park on an incline but it puts the front of the car higher than the rear, I'm not sideways. I have run HEET through the tank. I was considering putting some Lucas fuel system cleaner through it again. I've done that once before and the car ran really well with it. I don't think it's ever sat long enough to let the gas break down. But would it make much of difference if I usually filled it at half a tank? I always put Shell gasoline in my car in IA the 89 octane is their regular 91 is mid and 93 is V-Power. So I usually 89, and when I'm stuck filling up in IL I'll get 87, but it's always Shell or if I'm in a pinch Mobil. Once I did take gas out of a gas can. It was for our mower, no oil gas, it had been there for a while though. Thanks for the suggestion, I'll investigate further. Any other info will be greatly appreciated.

This may sound off the wall but sounds like a possible emissions system problem. I think you said you put on a different gas cap, First try and find an original one possibly in a salvage yard and try that. If no help then locate the charcoal cannister called evaporative loss cannister. Pull off both hoses and plug the one that is the vacuum hose with a golf tee or some other method. Now drive the car and if runs OK, replace the cannister. It's worth a shot and won't cost a lot. Good luck.

Fm Robert
This may sound off the wall but sounds like a possible emissions system problem As critically important as the emissions system problems are, I believe that a diagnostic code would have been set..

you might have the problem I had. What if finally found and you can read about in my post is the second cable on the battery. Remove all the rubber on all and look at where it is crimpted. Mine was green with corrsion and voltage was bad to main fuse panel under hood.