RPMs Bouncing up and down. - Engine Troubleshooting


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RPMs Bouncing up and down.

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Patches33001
Novice

Nov 6, 2017, 9:27 AM

Post #1 of 4 (2567 views)

RPMs Bouncing up and down.	Sign In

Hi, so i have a 1998 Pontiac Sunfire, and last winter i had trouble with the RPM bouncing up and down after driving it for awhile. Then it stopped for awhile once i replaced all the O2 sensors (which at the time was triggering an engine code) and this summer i replaced the EGR valve. But it snowed this weekend, and last night when i got home from walmart it started doing it again. With the dashlights on they kind of dim and brighten repeatedly with the engine sounds. I tested the battery and alternator and both were fine. There isn't an engine code, so what else would be the problem? Thanks![:)]
-Patches

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Nov 6, 2017, 9:33 AM

Post #2 of 4 (2565 views)

Re: RPMs Bouncing up and down.	Sign In

First eliminate all vacuum or air leaks in the system (very important)

. You may have a bad IAC ( idle air control) but try cleaning the throttle body first. Remove the intake snorkel, have someone hold the throttle wide open for you and scrub the back side of the throttle plate and surrounding bore with an old tooth brush and some carb cleaner. Be sure to spray some into the small holes next to the throttle plate. That should help stabilize the idle. If it still has a problem, replace the IAC.

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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

Patches33001
Novice

Nov 6, 2017, 9:44 AM

Post #3 of 4 (2557 views)

Re: RPMs Bouncing up and down.	Sign In

Okay, thanks, last time i took off the intake the throttle body looked fine, but ill check the backside just in case.
-Patches

Patches33001
Novice

Nov 9, 2017, 10:45 AM

Post #4 of 4 (2513 views)

Re: RPMs Bouncing up and down.	Sign In

Just cleaned the entire thing today, seemed fine. But we'll see how it helps! I found the IACV so if i do have to replace it in the future i know where it is. Thanks for the help!

-Patches

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