2002 Jeep Cherokee Gasoline Additive / High Idling

RELACHS

MEMBER
2002 JEEP CHEROKEE
V8
AWD
AUTOMATIC
62,000 MILES

Hi guys. My Jeep Grand Cherokee Limited is in excellent condition and had the 60K mile service done several months ago. It runs very, very well.

However, the last couple of times starting the car has been concering, as the idle is very high/rough with the start-up, but it drives normally. I also notice it's reving high while in Park.

In retrospect, I added a few gas tablets to the tank when I last put gas in, but I forgot to fill up completely. I filled the gas tank about 1/2 way.

Would too many gas additive/tablets combined with 1/2 filled tank cause this high idling? If so, can I just "drive it out"? Or is this coincidence and should I be concerned that something else is wrong?

Thanks,
relachs

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

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.