Thanks. The tech who just replaced the engine wiring harness said he did check those components and said they looked fine. At idle, the car's RPM will fluctuate between 500-1000, and when first accelerating it will backfire 2 or 3 times until it gets up to speed. Once over 30 mph or so the car will run fine.

I did have a look at the old harness- lots of broken insulation and frayed wires- a real mess. The tech said we would never be able to fix the problem if we didn't at least replace the harness.

This car is now very perplexing. We hate to keep dumping money in and not getting the problem 100% resolved. I thank you again for your responses.