I have a 2000 Chevy Tracker 4x4 with a 1.6 Liter 4 cylinder. It has developed a problem, and there are no associated error codes from the computer. It runs perfectly, but if taken on a long highway run, especially when the weather in warm (Alaska), as in never in winter, if the engine is shut off it will not hot start until you wait about 20 minutes. Then it starts and runs fine. In warm weather it will occasionally stall when idling in traffic for too long, or going at slower speed up a steep hill after a highway run. I replaced spark plugs and wires (needed after 101,000 miles) and did other tune up chores. No difference. A GMC dealer was convinced that it was due to both catalytic converters being plugged—I was skeptical but had them replace them. No difference. I was able to catch the engine when it wouldn't start and pulled a plug and attached a spark tester and there was no spark. I replaced both coils (no distributor in this model) thinking it may be a coil pack failure. No change. The only other think I can think of is a malfunctioning control unit (computer). Anyone have any thoughts?