Stalling at Hwy Speeds and High Temps

**Shudson105** · 09-29-2010, 02:54 PM

I have a 93 LT1 a4 with 88k miles on it. My car is stalling out when the engine gets to around 200* and driving at hwy speeds. The engine just spontaneously becomes unresponsive, check engine light comes on, but it will keep running (with decreasing rpms), while the throttle does nothing and the trans doesn't shift into lower gears. The engine will remain running (at very low rpms) until I stop the car with the brake and the engine will just shut off. It does not backfire. No codes at given either.

This issue has occurred before when my optispark went bad (last summer, 5k miles ago), however it has since been replaced (along with a new water pump, coil, wires, plugs, IAT sensor and both coolant temp sensors). The bad optispark would always backfire in this case. Again, the car doesn't backfire anymore...

It was suggested to me that one or more of my fuel injectors could be going bad and shorting out, but I have not yet heard of that happening and causing this issue.

Any help, thoughts, comments are appreciated!
Steve

**sunsetorangess** · 09-29-2010, 03:12 PM

Sounds like the coolant temp sensor "computer input sensor" is getting lazy or going bad, Have you checked your coolant? If you let it idle and get to temp will it do the same?
J

**Shudson105** · 09-29-2010, 03:56 PM

Both coolant temp sensors have been replaced and work correctly. I have verified that both with a temp gun and a scan tool. My Low Coolant light comes on if I turn the car on when the engine is hot, but will remain off if the car stays running and simply gets hot from driving or idling. I figured that is just cause its dirty. Both my overflow tank and the rad cap show full coolant.

**Shudson105** · 10-08-2010, 10:51 AM

I drove the car the other day back and forth to the local college and let the car sit in the parking lot till the fans turned on and off again and the car continued to run fine. I know the engine itself got hotter then the day it stalled out (or entered limp home mode), but I don't believe the engine compartment got as hot as it did when I posted my orig question.

The GM service manual lists intermittent problems that don't post codes as being caused almost exclusively by electronic or wiring harness related problems. It also listed the EGR valve, ignition and fuel systems as also being areas to check. I don't think the EGR valve would cause the computer to enter limp home mode. As mentioned in my orig post the ignition system is all new (including a section of the wiring harness).

Does anyone have any thoughts on what could happen to the fuel system to cause the computer to enter limp home mode?