99 Malibu Idles Rough

malibu

#1

I have a 99 Chevy Malibu with 155+ miles. The car has been running great up until a few weeks ago. When you have the car in park or at a stop the idle goes up and down almost to point of stalling. We’ve replaced the spark plugs, coils, module, oxygen sensor and pcm. Since the pcm was replaced and programmed it runs even worse. Any suggestions?


#2

My apologizes, the mileage is 115+ Other than this issue the car runs great.


#3

Try getting your transmission sensor replaced…or at least looked at.
I had a 91 Grand Am that was doing the same thing…Idling rough, up and down, and then when I tried to start off at a stoplight, it would die. I know it’s 8 years difference, and a different GM model, but that’s what worked for me when we’d replaced the ignition coils, gave it a good tune and all that other stuff…


#4

There may be a loose vacuum hose or other leak. Check the air intake to the throttle body.