SirRadiodude

I just purchased my first Ford truck and joined the forum.... and now I am in a bit of a pickle....

The truck:
1993 F-150 SWB XLT RC w/ 351, auto, & A/C


I am having an issue with a high idle 1500-2100 depending on load on engine (accessories). When I put it in gear it idles down to 1100 or so. I did ODB1 paperclip diagnostics and came back with a code 12 while checking only ignition.

Code 12: Idle Speed Control motor or Air Bypass not controlling idle properly (generally idle too low) - ISC

While running it displayed the following code

Code 412: Idle speed system not controlling idle properly (generally idle too low) - ISC

So (despite it being too high idle instead of low) I removed and cleaned ISC. No change. Believing the ISC was an original 17yo part I ordered and replaced it... no change. In between each attempt I did disconnect the battery to reset the computer.

What's left?

The truck has 122,300 miles and is not displaying a check engine light BUT it has to pass local emissions testing (inspection is expired) I got very good deal on the truck because of the idle and a leaking rear main seal. The leak I can deal with but this idle risks to tear up a solid transmission, burn mucho petro, and overheat a strong engine.

Last owner was meticulous about maintaining records and its had thousands of dollars or parts replaced and work done.

Any advice is good advice at this point.

91351

Try a new throttle position sensor

dhenke

Is it losing power or making a slight whining noise when driving? My brothers truck is doing the same thing and the cat is clogged.