Hello gentlemen, I have found myself to be in a bit of a pickle here. I acquired an '88 f150 with the 5.8 manual trans, supposedly new engine and I can say it is quiet as a new one. Only thing is, I have my doubts that this truck started life with the 5.8. So to the point, this truck sat for two or three years and I acquired it and with many new and rebuilt driveline parts I figured there would be little risk. I was wrong. Here is what I have done and changed out: drained and cleaned both (nasty) fuel tanks, new tank pumps, went through and cleaned the selector valve, new high pressure pump, fuel filter, remanned 5.8 ECM, new MAP sensor, TPS, ECT, IAT, IAC valve. I'm only listing the parts replaced pertaining to the fuel system.

Now this high idle has about made my hair fall out. I have yet to defeat it despite the research. Here is what happens - crank truck cold and it cranks fine, no problems, rpm picks up to 1500 and drops back down to normal after a few seconds (seems normal to me). From this point on, and it seems to be more pronounced as the engine heats up, if you apply any throttle at all and slowly/normally return to idle it hangs at 1900-2000 rpm. Give it a quick blip and it slowly returns back to about 800-900 rpm where it doesn't run so smooth, but ok with me. If it's racing at 2000 rpm during its hangup spell and I unhook the IACV the thing idles around 800-900, plug it back in and it returns to 2000. The throttle plate is not hanging open and I have hosed the manifold thoroughly with carb cleaner hunting for leaks, I have found none.

The tps voltage key on engine off is .88 V. during run it is about 1.1V. The throttle plate stop screw has been tampered with in the past, I have tampered with it more to set the tps voltage.

I did pull the codes earlier today and got an 85 and 96. The vehicle isn't tagged so I was doing one WOT pull briefly down my street and it started stumbling, felt to be starving for fuel, then died. Recranked and cruised back into the drive. That is when I decided to change the inline fuel pump (not sure if that even fixed it). I believe this thing has/had multiple problems, but the high idle is preventing me from doing any test driving. Sorry if I wrote a book here. Thanks in advance for any advice. I'm about to give up on this turd.

 

Is .88v the lowest voltage you can get when you adjust the Throttle Stop Screw ?

 

Yes, that is where it seems to bottom out. Closing the throttle plate further with the screw has little to no effect on voltage beyond that point.

 

Your throttle plates should be closed all the way.

Try backing the screw off the stop, then bring the screw back to where the screw tip just makes contact with the Stop.
You could use a small feeler gauge to help judge.
The Throttle Stop is to keep the Plates from jamming in the Body.
The screw is not for adjusting voltage.

You just want to be sure the Throttle Plates are closed all the way. Like if the Throttle Body was off and you were holding it up to the light, you could not see light coming through the closed Plates.


Do you have holes in your throttle plates?

 

I'll try that and see what happens. No holes in these throttle plates.

 

What is the TPS Ref Voltage; Key On ? Running ?

 

Engines are easier to diagnose over the internet when all the codes are listed, and in order of test.
KOEO - (O) Self-Test Codes = ?
KOEO - (C)(CM) Continuous Memory Codes = ?
KOER - (R) Self-Test Codes = ?

Check Base Timing?
Check Timing Advance?

Do you have any Non-Stock modifications?
(Air Intake? Smog System? Exhaust System? Ignition System?)

 

I have been on this forum for months now trying to figure out the high idle issue I have on my 87 302. Have replaced all the stuff you siad you have replaced even the ECM. my idle starts out sometimes ok then climbs up to 2500 rpms . I gave up & took it to a shop where they will do a smoke test for internal vac leaks --have done all the external spraying with carb cleaner etc. If you find a solution please pm me or post . & if I ever find the problem with mine I will do likewise. Also told the shop to ck. TPS voltage for me .. Ididnt have much luck trying it

 

Thanks vjsimone, I'm going to have to find another service manual, or probably the full volume, the factory one I bought doesn't even cover the efi system, I found that there was 20 degrees of timing with the spout connector out, Not sure what rpm and what the specs are though. Also, that the high pressure pump was cavitating on the rear pump, sounds like the selector valve is bad. I don't even know how to do the full code retrieval (I'm a honda and ford diesel guy) so I've got to study up and spend more time and money if I'm going to make this work.

Will joyce, I'll certainly do it if the day of success comes. Steep learning curve ahead though. Your post is discouraging, but I'm an advocate of reality, thanks for sharing.

 

At operating temp, I show your truck should have the timing at 10*BTDC with spout out. Your code 85 KOEO would be a a canister purge circuit failure. Code 96 KOEO or C would be Fuel pump circuit open, battery to PCM. Sandy

 

http://www.troublecodes.net/ford/eectest/

 

For what its worth ,the shop I put my truck in called yesyerday & said no vac. leaks after doing a smoke test. What they did find was a bad TPS sensor I had bought from Rock auto . .After putting another one in ,that solved most of the high idle issue they said. Said it wouldnt hurt to replace the throttle cables as it binds a little & keeps the throttle plates open a hair . You can kick the gas pedal to unbind & the idle is good . Havent picked it up yet , but I just wanted to share this info . . Also said a different throttle body may help , but not necessary --Good luck with yours.

 

so i took my tb off the 95 f150 5.8 cleaned it looks just like new again dawn power spray took 25 year of gum rite off New tps on .97 CT 4.66 wot New gasket new iac. relearn done did fine pulled back in and high idle got to looking the throotle was sticking wasnt shutting . the linking plat will bend when uesed as a prop the straighter i get that plate the better that truck runs look really close at the roller in the middle of the tb on back side it is in a little square hole 25 year of burn on oil it was sticky but look at the linkage plate on tb for gas cable thats the one ever person thats ever worked on has put there hand on it to reach something on the other side. going to take her for 60 miles or so today to see how that drinking problem of hers got she was starting to become an gasholic.