Throttle redlines a second after ignition.

I just changed my head gasket on my 2000 XJ. I got everything back together with the right torque specs and when I tried to turn it over the first time, the rpms redlined a second after it turned over and I had to turn the key off. I've tried different recommendations and it still does the same thing. I can't find any air leaks. I was wondering if it's something with the throttle body or one of the sensors. Here's another little piece of info: When I took the intake manifold off, I taped up the sensor orifaces and blasted off the manifold with a pressure sprayer. Could I have jacked something up by doing that?

What you describe is usually a massive vacuum leak at the manifold gasket. Recheck your work and make sure the intake manifold is flat and fully flush to the mating surface on the head.

I'm with Tim MN on this, but have you verified that the throttle is closed before starting the engine?

Yes to throttle question. I'll remove the manifolds again after work today and re-seat. I'll let you all know how it works. Thanks.

XJWillis said:

Yes to throttle question. I'll remove the manifolds again after work today and re-seat. I'll let you all know how it works. Thanks.

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if the throttle plate is closed, then the intake manifold is not seated proporly or the gasket may be torn.

You were right! I took off the intake manifold and it was not seated on the bottom studs. I should have been suspicious when that bottom bolt to the PS pump was such a bear to put on. I put on a new gasket when I changed the head gasket, so that was good to go. It runs like a Jeep again, Thanks!

"it runs like a jeep again"... Is that realy a good thing?

Kevinma255 said:

"it runs like a jeep again"... Is that realy a good thing?

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That means it will run til the gasket pops again!

Kevinma255 said:

"it runs like a jeep again"... Is that realy a good thing?

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for the 4.0, then yes it a very good thing.