Mechanics

ENGINE IDLES TOO FAST

1994 Mazda MX6

Engine Performance problem
1994 Mazda MX6 6 cyl Front Wheel Drive Automatic 165000 miles

Heyyy, I just like to say thanks for taking the time to answer questions on this site, when everyone knows, you guys could be doing other things more important but you choose to do what you do.

Moving on.
I recently got a tune-up cause my car was really in need of one. Everything was running nicely but I've noticed that the longer I drive now, the faster my engine will idle. Like. After 20-30 minutes of driving, the engine idle will be running around 1100-1300rpm say if was stopped at a red light. It gets to the point where I have to use a lot of pressure just to hold my brakes from stopping me from pulling forward. When the light goes green, I can reach roughly 40km/h without even accelerating.
I'll also notice that when I put my car into park, it will rev up to 2500 rpm. At times it will idle so high that the little needle will bounce up and down repeatedly like it will go up around 2600rpm and drop down to 1100 and then go back up again in a quarter of a second. I know this isnt normal. My car is slowly getting to be a discomfort when drivng. What could be the problem?

Thanks for any help!
Avatar
Jordanbotha
July 2, 2008.



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.

Rasmataz
Jul 2, 2008.
Thanks for the quick reply. Just a little extra info. This only happens on hot days during the day time when its above 24 degrees outside. When I drive at night, or in the evening around 9pm, my idle appears to be relatively normal and I can drive for several hours. It's just during the day time that its a nightmere.

Out of all the things you listed, is anything strictly heat sensitive and more reactive in higher temperatures? I know its not my tempertaure sensor cause its been replaced a few days ago, and my engine oddly enough doesnt overheat on the dash.

Thanks in advance for any extra help

Tiny
Jordanbotha
Jul 5, 2008.
Inspect and test the idle air control valve and throttle positioning sensor-

Rasmataz
Jul 5, 2008.
What caused the high idle was the throttle cable being too tight! Hot weather seemed to make the throttle cable tense up, thus causing the throttle plate to not fully close. I loosened the cable and now it idle's normally

J-

Tiny
Jordanbotha
Aug 30, 2010.