2002 Ford Ranger

Engine Performance problem
2002 Ford Ranger 6 cyl Two Wheel Drive Manual 140000 miles

Intermittantly when I push in the clutch coming to a stop the truck goes to nearly 3,000 rpm at idle. Turning the a/c on or loading and unloading the engine with the clutch will usually drop the idle to near normal.
I haven't seen the check engine light come on.
I tried physically putting my foot under the gas pedal and pulling up. No help.

Last time I wrote the truck had a terrible spark knock. 2cars recomended I clean the MAF with MAF cleaner. I did that and it seemed to help for a few days but the spark knock is back.
August 14, 2010.

Your symptoms seem to lean heavily toward a vacuum leak. That is the one thing that would cause both issues. The best way to check for a leak is with a smoke test but you can use a can of carb cleaner with the engine idling. Spray a little in any suspect areas and listen for RPM change to indicate a leak. Once you have eliminated any possibility of vacuum leaks, move on to the next step.

You may have a bad IAC ( idle air control) but try cleaning the throttle body first. Remove the intake snorkel, have someone hold the throttle wide open for you and scrub the back side of the throttle plate and surrounding bore with an old tooth brush and some carb cleaner. Be sure to spray some into the small holes next to the throttle plate. That should help stabilize the idle. If it still has a problem, replace the IAC.

Aug 14, 2010.
Sprayed the vacuum lines and around base of intake with carb cleaner but found no vacuum leak. Cleaned throttle plate front and rear and truck comes back to idle now. I drive the truck very easy but the spark knock is still awful going up a hill. I usually buy the 87 octane here in Kansas city from Phillips. The engine is the 3 liter Vulcan V 6. The check engine light is not on.

Aug 16, 2010.
Make sure your EGR system is fully functional for the pinging problem. Manually pull the valve open at idle and see if the truck tries to stall as it should. If it doesn't the passage could be plugged up or the EGR could even be the source of a vacuum leak.

There may also be a timing shunt along the harness somewhere that when removed, retards the timing by 3 degrees that should help also. Not positive about your model on that though. Check the EGR first though.

If you have a scan tool, make sure the knock sensor is working.

Aug 16, 2010.