Intermittent high idle and racing engine

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heppm01

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Wife's 2003 Montana intermittently exhibits a high idle (2500rpm) or racing engine while moving. When it happens it's so bad she needs to ride the brakes to keep the speed under control. If she turns the van off and restarts it then it is fine (for a while). Obviously she is not willing to drive it like this.

The engine is throwing some codes but I'm not convinced they are related. P0135 (upstream O2 sensor heater) started a few months before the issue popped up - haven't gotten around to swapping the sensor out yet. P0452 (fuel tank pressure sensor low voltage) and P1639 (5 volt ref 2 circuit) come and go - sometimes the issue happens without these codes and sometimes the codes trigger without the issue happening. (I've been clearing the codes periodically).

Seems to me that somehow excess air must physically be getting into the engine - I don't see how a bad sensor could play into this since there must be air to support the high engine speed. I've replaced the IAC and cleaned the port but it didn't make a difference, and I've checked the vacuum lines as best I could but it's darn near impossible to work in this cramped engine bay.

Any thoughts?
 
really no experience with this but could it be as simple as a sticky throttle cable ? However that would not cause the engine to surge .
 
Does it do it at idle ? Or does it do it only above 25 mph when the cruise is active. Could it be the cruise control going bad ?
 
Also i wouldn't let her drive it either .
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Unrelated to cruise. Once it starts it continues even if the vehicle is stationary, and I confirmed under the hood that both cables are loose. Goosing the throttle does not resolve the issue so it is unlikely a sticking throttle plate.
 
So apparently when I replaced the IAC I pulled on the tube coming out of the top of the intake snorkel hard enough to free the far end from wherever it plugs in. Pain in the a** to get to but hopefully once it is reseated the problem will go away. I'll keep you posted.
 
Got the tube reattached. While I had everything accessible I went ahead and replaced the TPS as well. I noticed there was a little oil on the interior of the sensor, inside of the O-ring. Between the IAC and the TPS the problem has been resolved.
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Glad to hear you solved it
 
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