01 XJ engine runaway.

[Wyojeepin]

I just rebuilt the 4.0 in my 01 XJ, and installed it. When I start the engine it acts like you are holding the throttle flat on the floor. The engine revs to atleast 4,000 rpm's (where I shut it off). I replaced the TPS with no difference, checked for vacuum leaks. The throttle valve never moves tho.

What would cause it to be at full throttle on start up? The only code was the TPS so I replaced it and cleared codes, no more have shown up.

 

[birchlakeXJ]

You have a massive vacuum leak.

The intake manifold is very likely not properly positioned on the head and is leaking air, which causes high engine rpms. The intake manifold must be properly positioned over small positioning studs which allow it to seat all the way and seal. If the intake manifold not properly positioned over those studs on the head, no amount of tightening the bolts will allow it to seal.

You wouldn't be the first one that this has happened to.........................

I'd start there.

 

[Wyojeepin]

thanks I will check that.

 

[Retlaw01XJ]

You have a massive vacuum leak.

The intake manifold is very likely not properly positioned on the head and is leaking air, which causes high engine rpms.

You wouldn't be the first one that this has happened to........................

Been there. Intake was hung up on the exhaust manifold flange.

 

[SicNastyXJ]

That is exactly what it is. I just finished rebuilding the 4.0 in my XJ and ran into exactly the same problem. loosened and readjusted the manifolds then torque back down cured it.

 

[Wyojeepin]

Yap ya'll where right, it ruined the gasket tho. Got a new one and reinstalled now it runs right, well almost. Now its missing, found #4 injector bad. Got a new stocker on order.