This had been a problem for a long while, outliving all repairs I have
done on the car.
Lately I have to drive on a daily basis, and this winter the problem
became a royal pain.
The colder the night was, the lower will be the maximum speed I can
get to. At that max threshold speed the car would buck, jerk as if
ignition is not happening, and can even stall, if forced.
The oddity is that warming up the engine on idle has little effect,
compared to driving under max achievable speed.
After about 5 minutes of driving, that maximum speed will start
increasing, after 5 more minutes it will gain another +10mph, and in
about 30 minutes I can drive fine at any speed until next cold night.
There are no error codes, starting, idling, stopping, accelerating,
going at 80mph are all fine, there's no jerking or stalling other than
in the situation described.
At warmer weather I won't notice the problem, or that max speed would
be around 70mph, where it doesn't bother me so much.
This issue survived:
* transmission rebuild
* three MAF sensors change
spark system change (plugs & wires)
* ICM change (ignition control module)
O2, camshaft, crankshaft sensors change
* new catalytic
* fuel filters change
Throughout the years it's as solid as my appetite. And it's as
disturbing. Imagine how you wake up in the middle of winter, you need
to drive to work, and you aren't able to drive above 20mph for good 5
minutes. Now imagine that you're a police officer, sitting in your
vehicle, enjoying your morning doughnut, and then a rusty old car
crawles right in front of you at a treacherously low speed, and then
you see it again and again, as I make several circles around the area
trying to get the car to the speed where I could pull on the highway.
This picture can make even the most breakfast-minded detective
I'm looking for any pointers, anything I could try to diagnose what
the hell is so profoundly wrong with my otherwise great beast.
It's a 1988 GM with 75K engine, no distributor (coil packs),