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First, I didn’t see an option to search the forum for previous posts to see if this might have been addressed. If I overlooked a way to search before asking the question, please excuse me.
Problem: 2001 Pontiac Grand AM 3.4L engine surges at idle back and forth between 500 RPM and 1,500 RPM. Rarely goes out of those ranges at idle. Mileage is 162,000. My parents owned the car for about 3 or 4 years and I bought it off them last year. Has surged like this for at least a couple of years. Doesn’t seem to affect driving, only idle. (Transmission does jerk at times as gears change, especially up hills but hopefully only needs some fluid – no dipstick so I’ll have to get it up on a lift to check fluid on transmission). FYI – has been a good car but paid $1,100 in repairs couple months ago for head & manifold gaskets, serpentine belt, platinum plugs, thermostat, fluids – had mechanic replace the other things while he was replacing the gaskets).
I’m suspecting to check for vacuum leak for the idle surge. Does that sound reasonable? I watched the video on using carb cleaner to check for leaks. Good move or should I be thinking along another line of suspected problem?
Thanks for any advice.
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+1 on checking for vacuum leaks –
Also inspect the plastic intake duct for any tears as well as a good visual on all your vacuum lines.
Any CEL?
Is your TB all gummed up with carbon?
I would also use some MAF cleaner.
For checking your trans fluid, make sure the vehicle has been ran for 10 minutes or so and leave the vehicle running when you remove that small plug at the side of the trans.
Thanks for the quick reply. I hate to ask this but I am more of a novice on mechanics, but trying to learn.
What is CEL?
What is TB?
What is MAF cleaner?
Lol.No problem on your questions 🙂
CEL – Check engine light
TB – Throttle Body
MAF Cleaner – Mas Air Flow cleaner, a chemical made by CRC.I would also look at the vacuum hose going to the FPR (fuel pressure regulator). Remove the hose and see if there is any signs of fuel in that hose whether vapor or actual gas. That issue usually causes hard starts though.
Thanks for your answers dreamer. No CEL light on. I’ll check the other things once this snow clears and after Santa visits since the car drives fine but I do want to resolve the idle thing. I’m sure it doesn’t help on fuel economy with the rough idling.
Merry Christmas!
I think you’re spot on by checking for vacuum leaks first as that is probably the prime suspect. You might also have a problem with the idle control valve. To check that try tapping on the outside of it while the engine is running, if the idle changes or reacts in any way then you might consider replacing it and rechecking for the problem.
Keep us posted.
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