1993 Honda Civic to fast cold idle

RUSSELL YARBROUGH

MEMBER
1993 HONDA CIVIC
4 CYL
FWD
AUTOMATIC
193,000 MILES

I ask this question a few days ago, the engine idles to fast when cold for about five minutes. Once it goes into close loop it idles fine. If I unplug the idle motor of either of the temp sensors it idles fine. You guys suggested a vacuum leak. I checked for that long ago, brake booster, PCV intake gasket, and any other thing that has vacuum on it. Besides if it was a vacuum leak when I unplug the idle motor and the rpm slows down, it would run rough or shut off. It doesn’t, it run pretty well. Also I can remove the air intake duct and filter, slide a restrictor across the intake for the idle air passageway and the motor slows down and runs at the correct rpm. Like I say once it warms up and the ECM goes into close loop, the motor idles fine around 600 rpms. I think something is setting the idle steeper motor to run at the higher speed 1900, 2000 rpm, I just can’t figure out what. I get no codes set in the ECM.

Thanks for your help anyways.

1 Reply

KHLOW2008

MECHANIC
41,815 POSTS

Hi Russell yarbrough,

When the engine is cold, the rpm would be higher as the fast idle valve isopend to allow extra air to get past the throttle body. This is specifically designed to operate thus and if after warming up, the idling is correct, there is nothing wrong with the system.

The cold idling speed would vary according to the temperature and the main controlling item is the fast idle thermo valve located under the throttle body.

If after warming up and idling is till high, the the thermo valve might have worked itself loose allowing excessive air past the throttle body.