Engine revs up in the park

[Wingback806]

Hello guys I have a 95 Ford bronco XLT and when I put it in park every now and then it revs up to about 1300 RPM and stays like that for a while. What you guys think the problem is

 

[miesk5]

Yo W,

Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19

http://broncozone.com/topic/14269-code-reader/?pid=74587&mode=threaded

Some basics;

The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.

Run it around to heat the engine up and shift thru all gears including Reverse.

Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual & release clutch.

Then turn off engine, all accessories/lights (close driver's door) , etc.

Do KOEO test First

Post Code(s) here according to:

KOEO

&

KOER

****

THIS WILL PROBABLY HELP DIAGNOSE A SENSOR OR WIRING or vacuum leak......

and also: Throttle sticking or linkage binding."

Usually a bad or a good IAC would result in a low, erratic idle..my 96 had a good IAC, but the throttle body holes were mostly clogged... have been using a TOP TIER Gas (Shell) but now I am certain the station owners are subbing non-Shell gas in their tanks)

However, I have heard of a bad IAC causing a high idle.

Read this by Mike:

Ford vehicles with an Idle Air Control Motor (called IAC) that have idle problems and sometimes noise concerns can be diagnosed in the following manner. For high idle problems, try unplugging the IAC motor. If the idle drops, its usually due to an input signal to the computer which results in the computer raising the idle speed. If this is the case, look at all of the computer inputs to make sure everything is up to par. If the engine RPM does not drop when the IAC motor is disconnected, then either the IAC motor is not functioning properly, or, there is a vacuum leak in the engine. Stop the

engine, remove the IAC motor and block off the passages. Restart the engine to see if there is any change in engine

RPM. An idle speed higher than base idle specs indicates a vacuum leak. If the engine RPM is at base idle specs, then

the IAC motor is bad. Resistance specs are 7-13 ohms. A good resistance reading does not necessarily mean that the

IAC motor is good. Occasionally, an IAC motor will become weak, and will actually bypass too much air, causing a

high idle condition even though everything else is operating properly.

Read more at

http://web.archive.org/web/20030411092204/www.carquest.com/techbulletins/engine_controls/tt3q00.CQ.pdf

 

[Wingback806]

Thanks for help