Engine Performance problem
2002 Ford Taurus 6 cyl Front Wheel Drive Automatic 173, 00 miles
I just installed a new set of plugs. To gain access to the front cylinders, I removed some vacuum lines. After replacing the lines the car now idles too high. The lines are intact with no apparent leaks. The speed initially is @ 1800 RPM. After about 20 seconds it will gradually drop to @ 800 RPM. Shifting into drive or touching the accelerator will send it back up to 1800. The time that it takes to drop back down to correct idle decreases as it warms up but never gets less than about 8 seconds.
There was no problem with the idle before I changed the plugs. It seems reasonable that something was disturbed while changing the plugs but, on the other hand, maybe it is an unrelated coincidence. Any ideas?
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.