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A vacuum leak is unlikely to hold RPM that high. 1st inspect throttle plate not closed all the way, possibly hung up, or cable pulled too tight holding throttle open or accelerator pedal not releasing completely. If ok, next would be a computer controlled issue , Possibly idle speed control motor or throttle body assembly if not cable operated .
Testimonial: "no way george. I have tryed everything and benchchecked ba lot.Hard to find vacuum failure,brakebooster/vsc also capped off,to see where the leak is coming in."
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Check for a possible leaking vacuum system, maybe the vacuum booster is leaking, that would explain the idle being affected by stepping on the brake pedal.
make sure all the connectors are on the throttle body and nothing is binding. Jeeps have a service bullitin about something like this. Try removing the IAC and clean the pintal area or replace the IAC. I have a 93 wrangler and I have had this happen to me. I cleaned it and it worked. Try disconnecting the battery for a few minutes then try it again. This will reset the IAC to MIN. If this allows it to start at a lower RPM then you Isolated the problem. Try tappping on the IAC also. It may be sticking. Either way if anything make a difference then you will prabable need An IAC.Make sure you have no vacuum leaks anywhere. A vacuum leak will hold the idle higher also and the computer will close the IAC as far as possible to compensate.
Heres why you have a high RPM
When you start the car if you have a stuck open IAC or vacuum hose leak the O2 sensor will see this extra air and add fuel to compensate to maintaim a 14.7 to 1 ratio but also the computer will see your foot is off the gas and the throttle position switch is closed. Under this condition the computer will want a precalibrated RPM which is between 660 to about 750 rpm +or- some. It will close the IAC till it reaches this level.
if you have a vacuum guage handy hook it to your manifold and if your reading is under 15 hg then you have a manifold gasket leaking or you could just replace the gasket.
Well, the engine requires backpressure and a ventway for the exhaust; however it shouldn't be causing that.
The temp is explained simply by the speed of the engine, that's a really high RPM for no load and it's gonna head up quickly. Try seeing if you can adjust the throttle itself and see if that's incorrect somehow. I'm not sure on the prelude but I believe the cable is adjustable.
The only things holding the engine from going to such an RPM is the throttle itself. If it's opened to far the RPM will rise by giving the engine more air/fuel through the intake. So make sure that throttle is closing. I believe it should just about be completely shut on that car. I think it's only about 1/8th inch gap or somewhere close to that. I'm not positive on that and you'll have to work with it to find it.
If you can't adjust your cable, try disconnecting the cable completely and see if the throttle closes. If so the RPM should go down to an idle or somewhere close for you. Hope this helps bud!
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