Vacuum?

[RSWiser]

I recently replaced the freeze plugs on my 99 Cherokee Sport 4.0.

Once I had everything back in place I started it up and it immediately ran up to the redline and I shut it down. Checked everything and tried again. Same result.

I loosened up the intake to make sure I had it on the guide posts. Everything appears to be in the proper place and torqued in the proper sequence.

Today I had a friend with me and when I started it we could hear a vacuum leak at the rear of the engine. I have a new manifold gasket and we both inspected it and everything seems to be sealed properly.

Could a vacuum leak in one of the lines cause the engine to rev to the max?

Would resetting the PCM do anything?

RSWiser

[4.3LXJ]

That is a big vacuum leak. Did you leave the brake booster line loose? Is the butterfly in the throttle body seated?

[Mudderoy]

I can't wrap my head around this. The butterfly would have to be open, probably wide open to hit 5k rpm.

[XJ Wheeler]

Left my booster vacuum off one time and it only went to 2500~. I'd suspect that new gasket or something holding the throttle open like mentioned above.

Also, just as a precaution double check all the sensors are connected and didn't get damaged.

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[NW99XJ]

I'm wondering if the TPS (throttle position sensor) is jacked up.

[XJ Wheeler]

If you unplug the tps the rpms would change if it was the source right? If so, worth a shot for free!

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