1988 Dodge Ram engine stuck on fast idle

1988 DODGE RAM
170 MILES • V8 • 4WD • AUTOMATIC
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SIXOIL155
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I have a 88 ramcharger with a rebuilt 318 engine (about 35000 miles on it)with a throttle body.
After starting it hot or cold the idle races up and will not come down.
the idle speed motor seems to be moving ,but very little.
The egr valve has about 50,000 on it and i pulled the vacuum hose off it but did not see any change in idle speed. the map sensor is 3 years old.
Any suggestions as to where to start ?
Aug 1, 2008 at 4:18 PM
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RASMATAZ
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Too fast an idle speed. If an engine without computerized idle speed control is idling too fast and refuses to come down to a normal idle speed despite your best efforts to back off the carburetor idle speed screw or air bypass adjustment screw (fuel injection), air is getting past the throttle somewhere. Common leak paths include the carburetor and throttle body gaskets, carburetor insulator spacers, intake manifold gaskets, and of course, any of the engine's vacuum fittings, hoses and accessories. It is even possible that leaky O-rings around the fuel injectors are allowing air to leak past the seals. Another overlooked item can be a worn throttle shaft and a defective idle speed speed control motor/valve stuck in the extended (high idle speed) position/throttle position sensor. Also the throttle plate could be binding in its bore and kinked accelerator cable, coolant temperature sensor might not be operating properly misleading the computer that the engine is still cold and computer throwing fuel at it raising the idle speed.
Aug 1, 2008 at 4:23 PM
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MERLIN2021
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Disconnect the throttle cable and see if the idle comes down, if not have a look at the butterfly shaft for wear...then check the TPS for bad spots.
Aug 1, 2008 at 4:25 PM
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