ChadLunsford

Randomly when I start it up or just put it in park it will rev itself up to like 2500rpm, it actually hit 4000rpm once. We have no idea what it could be, a friend said it could be a vacuum leak. Any ideas?

go-part

Vacuum leak or a faulty IAC(idle air control valve) could be causing a high idle.

http://cdn3.autopartsnetwork.com/ima...AC291_BACK.jpg

ChadLunsford

Thank you ill look into it!

jnicewan

Do you get a check engine light or any codes? Those were notorius for IAC problems but most of the time they fail the other way and cause a low idle or dying. If its a SOHC 4.0L the IAC is located under the plastic cover on the upper intake, if its the OHV 4.0 its on top of the upper intake behind the throttle body and shifted to the LH side, if its the 5.0 its mounted right on top of the throttle body. When the problem is present sometimes you can tap on the IAC with a small hammer or screwdriver handle to unstick the valve. You can also try removing it and cleaning the gunk out of it, sometimes this works and sometimes works only temporarily.

Do check for a vacuum leak but on MAF vehicles vacuum leaks usually dont cause high idle concerns but its a good time to check the vacuum lines, PCV and crankcase breather hoses. I have also seen TP sensors do things like that but its rare and usually sets a ck eng light.