strange idle?
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Senior User
Joined: Nov 2003
Posts: 152
Likes: 0
From: KC
strange idle?
I have a 1990 f-150 with a 302 efi when i start it the engine revs up to about 1500 rpms, and then it will drop below 500 rpm, then back up to 1500 rpm again, then back down, and it will do this for about 30 seconds, and then it will idle perfect around 700-800rpm, what causes this, sometimes when it drops below 500. it will die completely, the truck runs fine other than that, i was just wondering what could cause that? thank you
Elder User
Joined: Feb 2004
Posts: 553
Likes: 0
From: North Bend Washington
does this happen only when it's cold? mine does this every morning on a cold start no matter what the outside temp is. i've cleaned out the IAC and has helped. also what aggravates the problem is if there is a injector that has become partialy cloged, likes to drip fuel instead of spraying, (another problem i have). this one is apparent when the truck has cooled down some what (1-2hrs) idle will do the same thing and i can also smell a rich fuel condition, all most as is it was flooded. hope this points you in the right direction
Tuned
Joined: Apr 2003
Posts: 394
Likes: 13
From: 13th Colony
Could be a vacuum leak, the computer is hunting for the right fuel mixture. A dirty IAC may cause that too. Check for vacuum leaks and clean IAC with throttle body cleaner, not carb cleaner. Carb cleaner may damage plastic parts.
