Yes, an electrical load drops my rpm from steady. It goes down and oscillates a little bit. The battery is somewhat new and the problem existed before and after the new battery installation. The alternator is charging the battery, with about 14.5 volts going to the battery. So, I know that it is working, but perhaps it should be working better? I see my engine is grounded in one place to the chassis. I am not sure what else is grounded.

Yes, the brakes too load down the rpm at idle. All hoses seem to be connected and not cracked. I don't hear any noises - although I have not used a doctor's scope.

No squeeling sounds. But, at initial cold start I hear rattling-type sounds that go away once warm.

Any more suggestions or how to test?

 

Not unusual on an older car. If the noise is still there after the car has been driven for a few minutes and everything is up to normal operating temp, then I would worry.

If the O2 sensor has more than 100k miles on it, I would replace it with a generic O2 sensor. Newer O2 sensors can last indefinitely if the car is stock and not turbocharged or chipped, but the ones used 15+ years ago did not. To understand O2 sensors, rear this : Intro to O2 sensors

 

But if the O2 sensor was the problem, you would be getting a CEL & the ecu would revert to "closed loop". I also don't think it would cause an inconsistent idle.

Get a haynes manual for your car and follow the steps under checking for vacum leaks. The fact that your breaks contribute, points to vacum.

If it happens when you use electronics, I still think you should have your alternator & battery checked (reguardless of age). Autozone & Advance Auto Parts perform this service free of charge. Mabye you got a defective battery?

 

It seems logical that the O2 sensor could be causing the rough cold idle. What else is temperature sensitive to the system?

The warm idle is fine, except for the slight change when a load is applied.

The cold idle has rpm needle bouncing around.

 

Problems solved.

Three main things: 1) timing belt was loose - so it was tightened. It was making a noise when cold but disappeared once warm. 2) distributor had tiny metal filings in it, perhaps when remanufactured - so it was cleaned. 3) the timing was changed slightly.

Now the car is running perfectly. The cold and warm idle rpms are back to normal!!!

Thanks for all the hints!