Long time reader, first time poster. I’ve searched the site and haven’t found my issue discussed, although one was close from Mr2000gt but ultimately had no solution. Please forgive me if I’m out of place here. I’ve got a 2002 3.8 N/A 40th Anniversary Grand Prix GT with about 170,000 on it. I picked it up about a year ago and did a bunch of the regular maintenance stuff that hadn’t been done yet (or in a while) and replaced some worn suspension parts etc. It’s run flawlessly since. It has needed exhaust since I bought it but I was playing the band aid game until I could get to it. Forgive the length of this but I’m so confused by this I figure the more info I give you it might help eliminate a bunch of things and/or find someone with the exact same problem and a quick solution.
So here’s the problem. About 5 weeks ago I’m cruising along about 50mph and the engine suddenly just shuts off. No sputter, cough, weez, choke or puke; just shut off.? Fuel? Check, Battery check, Belt on pulleys, Check. I restart the car and it lights first try and idles smooth as usual. I drop it in gear and drive off like nothing ever happened. OK, That’s odd. About 2 miles later after the same 50ish mph driving, it shuts off again. This time with a little stumble; the same type that in an older non-injected car would induce some right foot massage to keep it running. I try a restart (neutral) on the role and it won’t light so I coast out of the way and put it park and try an immediate restart. It lights and stalls immediately 3 times before finally choking to a start. Of course exhaust is black and rich as hell from the failed attempts but is now absolutely fine. Smooth idle start driving again. Mind you, there has been NO SES light at all! I go through this process a couple more times until I get it home and scan it. There was one code (I think P0420 catalyst below threshold) which wasn’t a surprise as I’ve gotten it before with some other stuff that had been going on and I figure was related to the rotted out exhaust. When the other repairs were made all codes were erased and no P0420 code or other until this mystery began.
I start down the road trying to figure this out with no help from the computer, no codes. I’ve recently replaced the fuel pump and filter and fuel pressure was 44psi at the rail. I have a smooth running non-misfiring engine so I suspect the ICM is in perfect working order. I start thinking that maybe the cat is plugged (known to usually go south by my 170K miles). No big deal I need exhaust anyways so I buy a new cat and a cat back system. I’m going to spray down the nuts/bolts for the downpipe and I happen to catch a drip out of the corner of my eye. I stay there for a second and I see it again. At first I don’t think much about it because the hood has the scoops open to outside air and it has been parked in the rain for 2-days before I could get to it so I’m thinking rain got in, hasn’t been run, it’s nothing. I go to spray the nuts/bolts down again after about 10 minutes and I see another drip go by. I pay more attention and see that I have a coolant leak at the throttle body and it’s going off the elbow onto the bell housing. I think ok this is the problem because it’s sucking coolant into the intake and causing the problem. I install a new throttle body gasket, thoroughly clean the throttle body because it was completely ganked up and had some coolant in the intake along with a bunch of sticky oily goo. (I am not familiar with the NA 3800 so I have no idea if this is the normal condition of the intake interior for a car with this mileage).
I turn the key and it starts right up idles fine and the scanner is hooked up looking at live data and everything appears to be in working order. After about 1:52 it sputtered and saved itself. I figure it’s the residual coolant and/or goo I couldn’t get out of the intake. It runs fine at idle for about another 13:30 and then just stalls. No sputter, stumble, choking, nothing. Temp on the scanner was at 164. It starts right back up and runs for another 20 minutes before stalling again. Next attempt to start I get the same as before; lights with immediate stall 3-4 times then chokes to a start and idles fine. I take it out and drive it thinking maybe a little more load and heat will improve the condition. Nope. After a couple miles of 50-60 mph driving I come to a light and take my foot off the gas and it stalled without incident. This time it really didn’t want to restart but I did the pedal to the floor and turn the key till it lights, which it did and it ran fine all the way back home. On the restart I ran it to 6,000 rpm shift and stayed in it to the 2-3 shift and let all the way off. It just idled down to normal at 40 mph I accelerated again and it was completely smooth and drove like nothing had happened. Still no codes or SES light.
I’ve checked the grounds, fuses, and relays, swapped the ICM from my GTP, unplugged the MAF, and looked for any damaged wires or connections all with the expected outcome. I checked the plugs on the front bank and an easy one on the back and all were normal in appearance with no wetness or excess carbon. I went ahead and replaced the cat and installed the rest of the new exhaust and nothing has changed. It basically does the same thing as before. The only change was today it sputtered and saved itself at about 40 seconds and stalled out, again without fanfare, after about 15 minutes and 164 degrees according to the scanner. Again no codes or SES light and nothing seems out of spec. (All dash lights come on when it stalls, as they should and go off on the restart so the bulbs are good) I haven’t swapped the IAC from my GTP but I don’t necessarily believe that’s the cause as I suspect it would throw a code if it were the problem. There is no coolant visible in the oil; none on dip stick, none on oil filler cap, none visible in the head. I rechecked the throttle body gasket to see if there was coolant in the intake as before, but it was as I left it, mostly clean and dry. I haven’t gone to the trouble of doing a compression test as I have no evidence that a lower intake or head gasket issue is present. The thing that I find interesting is that it stalls at about 15 minutes (probably varies with outdoor ambient temp) of idle run time or 164 degrees. Does anybody know what commands come at that temp? Any advice/help is much appreciated.
Originally Posted by GrandPrixGT1
