High RPM on starting

[omarsifu]

My 2003 Jeep TJ 4.0 had a broken rear exhaust manifold. The part has been replaced, but once the mechanic started the engine the Jeep went crazy! Super high RPMs. He got in there made sure every bolt was tighten, making sure the intake sat correctly, as well as throttle body. We decided to replace the throttle response sensor and air idle sensor on throttle body to make sure these weren't the cause of the problem. On our second try, the jeep rpms dipped lower by still started high. What can be the cause? What can cause the rpms to shoot out of control? Any help is appreciated.

 

[Jerry Bransford]

Simple, he didn't get the intake manifold properly reseated against the head causing a big vacuum leak. He'll have to redo pretty much the entire job over to get it seated properly. Caused by rushing the intake reinstallation part of the job.

 

[CharlesHS]

I would recheck the intake manifold and vacuum line for the brake booster for vacuum leaks.

 

[JKP]

Vacuum leak. Most likely what Jerry said.

 

[omarsifu]

Appreciate the feedback, very frustrating.