Weird Idle

mn12sc35th

Registered User
I'm having a sort of strange problem at idle. It's on my 91 NA V6. In drive at idle it usually runs 6-700 rpms (800 in park) sometimes it will rev up about 500 and back down repeatedly on it's own. Sometimes in drive at a stoplight if the brake isn't in hard it will try to move. What could cause this? No check engine light no other symptoms.
 
Would cleaning the IAC help? We ended up having to put an IAC on it about 2 yrs ago as we broke the end of the plug for it and couldn't seem to fix it. I'll also check closer on a vacuum leak. Thanks for the info.
 
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