88 f150 5.0 efi
Been having a problem diagnosing a high idle.
So far, I had to replace the TPS- (this died months ago, I was warming it up with my foot on the pedal when it was cold),- no problem, but I figured it was time to replace it since its gonna start gettting cold out, -and its the right thing to do.
I removed the throttle body,-carefully- disconnected the IAC connector
then removed the TPS I cleaned out the throttle body ports on the plenem
and cleaned the throttle body itself, i did make the mistake of not removing the IAC valve mounted on the side of the TB when I was using the Gunk, and i know it got wet from it-(*which I Now Know its not supposed to come in contact with any engine cleaner,) and after putting it all back together, I plugged in the Battery, and started it up. The Check engine light went out, and It raced at a high Idle as it should have -until it reached operating temp, then it dropped back down to a low Idle. Things were ok as I thought.. within about 8 to 10 minutes into its low,regular Idle, the check engine light kicked back on and it went back to racing at a high idle I stood there looking at the motor shakin my head, then I reached over and unplugged the IAC, -the racing idle stopped,and went back to normal
-I figured that this had to be the problem cause it got soaked in Gunk..-So, I went out and replaced it with a new one this morning..no-change it races until its warm, then it Idles at the low rpm for about 8 minutes or so, then out of nowhere, the engine light goes on, and its racing at a high idle and wont kick down. -I doubt theres a Vaccume leak only cause it would be racing at a high idle constantly..I dont know..does the TPS and IAC run off of each other? meaning, If I disconnect one. will it burn out the other?...- anyone? any ideas? would appreciate it.

 

honestly i do not know if they run off of each other. what code is the code reader bringing up

 

did you reset the computer?

if not, do it now.

 

I dont have a code reader, Ive usually used the old "paper clip" method to draw out and count the flashes, but this check engine light isnt flashing, its just dead on .
any work that Ive done on it in the past, Ive usually disconnected the Battery for about an hour, and then connected it and ran the truck for a few miles so the computer re-adjusts itself..-never had a problem doing that.

 

so did you, or did you not, reset the computer?

 

I guess? to the best of my knowledge, andfrom reading through the Haynes book, they as well suggest disconnecting the BAT to reset the computer.
-If I'm doing this correctly the check engine light should go out..and it does.
but, within 10 minutes after operating temp, it comes back on with the motor racing at a higher idle..
-Ive heard of some kind of diagnostic reset, but only in reference to newer models..I've never really went looking for any diagnostic tools for the truck only because of the self diagnostic paperclip trick,and flashing the codes that are listed in the Haynes manual..but at this point I'm open to newer suggestions.

 

that should reset the computer as far as i know. if the light keeps coming back on then there is probably a problem that the computer keeps picking up on. does the truck ever die out on you if you are getting on it, then come of a quick stop or anything, or just idle really high?

 

Proper sequence is important.

Disconnect the battery for a few minutes.
Reconnect and run engine till it warms up and the check engine light comes back on.
Then shut off truck and read the stored codes using the paper clip flashing CEL system.

FIND OUT WHAT CODE IS TURNING ON THE CEL.

 

sorry, Ive been in and out all day on this,just got back in from messin w/it
-agin..
Nope doesnt cut out on me, just runs high out of nowhere..
-this is all really recent, after the cleaning and replacement of the aic, and the tps sensor..it seemed that i fixed it fine, the light went out,ran at a low Idle..then BAM light goes on,Idle increases..
I just came in the house from workin on it..
--What i just did,: I backed off the dead stop screw that stops the linkage-lowering the idle/closing the butterfly's more..it lowered the idle without me detaching anything..but the check engine lite is still on..
then just to see what happened, I disconnected the AIC and the motor konked out..thats supposed to happen..Right?? -i mean ,if the IAC is working?..I plugged it back in, and started it up its at a low idle..engine lite still on.
but it was at operating temp too. Im up in Massachusetts, and its still close to *90. outside still, so its gonna stay warm under the hood for a spell anyway. dont know what else to do.

 

What code is coming up when the check engine light comes on. The IAC being unplugged will not harm the TPS one bit and vice versa, but driveability will not be great if either is left unplugged.

 

No code, usually its supposed to flash, like it has in the past when somthing is crapping out,or about to..I just have a straight "CHECK ENGINE" lite,
-Whats been going on, is that I changed the TPS and unplugged the Bat before I did it, plugged everything in started it up,- the light was out.. and it raced at a high idle,got to operating temp, then lowered its idle..everything seemed fine, about 8 minutes later BAM the lite came back on,and it was racing high
I dont know, but im gonna guess that at a low idle its probably at around 800-900rpms?? but when it kicked up it was about mabey 1200-1300,mabey 1400 rpms?
its not racing like its gonna blow or somthing, but id say its doing about 30mph I took it out around the block acouple of times so the computer was reset and thats the extent of it..it never came back down.
The codes......no flash, just dead on and i did unplug the AIC and it ran fine..really, normal idle.. but this isnt right..I have two brand new AIC valves and their both doing the same thing..mabey its not them?

 

You have a steady-on check engine light when trying to pull codes with a jumper wire?