93' bronco high idle problem

[Metalhead_24]

hi,

just got a 1993 bronco V8 351 5.8 ... i was told by seller that the idle control switch was bad. I've replaced it

and it's still idles at 2.5 rpms. My buddy told me it could be a vaccum hose but not sure . If anyone has any idea

of what could be the cause please let me know.

thanks for your time

 

[92bronco_in_progress]

sounds like a vacumn line

 

[miesk5]

I agree with 92...

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 hloes 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. Diagnosing an IAC motor and its ... read more here

-----------------

Do a Self Test for Diagnostic Trouble Codes (DTCs) by our pal BroncoJoe19

Do both KOEO and KOER; latter test needs engine @ normal op temp.

Also, a bad TPS would result in a high idle

Throttle Position Sensor (TPS) Function & Diagnosis TSB 94-26-4 for 93-95 - DTCs 121,122,123, 124, 125, OBD II Codes P0122 and P0123

Source: by Ford via miesk5 (Al M)) at comcast.net

Long article, but any DTC found will narrow it down - and read this too in the TSB: "To minimize the replacement of good components, be advised that the following non-EEC areas may be the issue:

Excessive blow-by

PCV malfunction

Vacuum leaks

Fuel pressure

Throttle sticking or linkage binding."

Suggest buying a Vacuum Gauge..one of the most valuable troubleshooting tools.

 

[Metalhead_24]

Thanks guys,

very helpful haven't checked it yet but i will. i'll post back with more when i do and be sure to let you know what it is when i find out.

thanks again.

 

[Metalhead_24]

hi,

The idle problem was the TPS.. runs great now!

thanks again

 

[Yardape]

Thanks for posting your results and the fix. Thats a huge help for others on here.