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2007 Jeep Wrangler Rubicon 4WD 2dr

2007 Jeep Wrangler
Trim Info:
4-Wheel Drive, 2 Door, 4WD Sport Utility Vehicle
17 mpg city / 19 mpg hwy
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March 21, 2013, 8:39 am

Victor L

Question: what would cause a car to rev up immediately after starting?

I recently did an engine swap in my 98 wrangler inline 6, and used my previous motors components that were all working fine with my previous motor. Once i built it back up and turned it on for the first time it started to accelerate on its own so i immediately turned it off. i tried it again and the same occurred. I read online that the intake manifold if not seated correctly would cause this so i bought a new intake/exhaust manifold gasket and installed it and made sure the manifolds were both seated correctly and bolted down tightly. i also double checked my throttle body and all seems normal. any ideas what else could cause this?
i know that my heater core is severely clogged, but would that cause the motor to accelerate on its own so high?

March 31, 2013, 9:27 am

Elizabeth K

The heater core would not affect it at all. Assuming it runs at high rpms right away (not after a few minutes or after it warms up) you are either getting too much fuel and air, or the ECT (engine coolant temp) sensor is sending it the wrong reading (when you first start it, the only sensor the computer is listening to is the ECT).

And how high is it accelerating to? Sometimes an engine will idle too high after the battery has been disconnected. The solution is usually to let it warm up/drive it and it will come down on it's own. But if it's revving up really high, then that's probably not the case.

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