Last week We took the family to Maine on vacation. While on the Mass Turnpike, we got stuck in a traffic jam for about 30 minutes after driving for about 45 minutes. The external temp on the mirror read about 102F. At first when we stooped things seemed ok, but after 4 - 5 starts from standing to about 15 - 20 mph than back to a standstill, i noticed something best as I can describe a rolling miss with the engine. The idle dropped to under 500, and when in gear, while depressing the throttle slightly, it felt like not all the cylinders were firing. After I noticed this, I would shift to neutral every time we stopped to raise engine speed to keep it running. The check engine light would switch states from flashing to steady on. When traffic started moving, the engine seemed to start running on all cylinders and the check engine light went out. When I finally was able to get off the turnpike, I had it scanned for codes. Nothing was found! Any ideas on what this could be? I bet the high ambient temp and resulting high under-hood temps had something to do with this. Without any DTC's I want to fix it but don't want to repeatedly load the parts cannon at it. What comes to mind is a temp sensitive PCM or crank sensor. What is in the truck is original from when it was built, Any ideas on what it could be or how to proceed? Plugs and fuel injectors have been replaced about 20000 ago. I don't want to break-down on our next trip.

Thanks,

 

When was the last time the fuel filter was replaced? Partially plugged one could have let it start vapor locking in hot traffic.
They are a 30k mile service item. And will not set codes

 

It is important to determine why the check engine lite illuminates, but more important to determine why it is flashing.
When it is flashing it can be doing damage to the vehicle's catalytic converter and that can be expensive to repair.
When you shut the engine down the codes apparently are being erased and the only way to get them , the scan tool needs to be connected and vehicle checked before the engine is shut down.

Might be a good idea to make sure the cooling fan(s) are functioning as required. That could be why it began to clear up once the vehicle started moving.

 

repairman54, good thought, the fuel filter. it was changed 13,756 miles ago. I also recently replaced the fuel pressure regulator as this was causing a surging due to an unsteady fuel pressure.

hanky, the fan is running normally and I changed the belt 4600 miles ago. The solid and flashing check engine light did not last long after we started moving and was gone within a couple of miles. I still suspect some sort of heat soak condition as the cause of this. In retrospect, I don't think having the AC on to keep us cool helped the situation out at all.

The last time I had an issue with this truck, the check engine light would start flashing at speeds over 62 and come on solid over 70. Dropping back to 62, would go from solid on to flashing then go away. Misfire counters indicated cyl 1 and 6 to have misfire counts. I searched a long time online and found a mechanic from Alaska who described the exact same problem. He reported to fix the problem with a crank relearn using the existing CPS. I did that and it's been running fine for years. I wish I had my scan tool with me when this started acting up, but my scan tool is one something I normally bring along on vacation. Since I still have the original CPS in the truck, maybe it is time to replace it. Do they often have problems with heat soak?

 

I've had a fuel pump heat up and slowly lose pressure. Would drive fine in cooler weather but in summer heat after 30 or so miles it would start to die out.
Didn't figure it out until I drove it some on a hot day and let it idle in the driveway with the pressure gauge on it. Was a '95 Taurus so no scan tool checking of fuel pressure.