high idle problem on a 4.0

[Ranger44]

Did you ever replace the TPS?

I do know that at one time my truck idled weird(high), would hold rpm at about 4k when the clutch was in, and slowly come back down, it'd also be go or no go. A slight press on the pedal was accelerating way to much and before I knew it I'd be up to 40mph, let off and feel like I was engine braking. Felt like the IAC wasn't smoothing out the accelerator input as much as it should have been.

Now, I did just replace the IAC, it tested a little weird. I kept the old one hanging around. Then I looked up codes.(Good ol' flashing CEL), and got a shorted to ground TPS. Checked the wiring like I mentioned before. I even cross check other ground wiring in the same area for a short from wire to wire. Nothing. So i just determined the TPS was shorted internally. Replaced it with a Borg & Warner and it still wasn't right.......WTF. So I decided to put the orig. IAC back on. Problem solved....... So, just replacing a sensor doesn't always help. I should have just left it alone. BTW, that IAC was bad from the factory. Go figure.

The PCM does rely on the TPS, and ECT on idle, fuel delivery, etc.(open loop) before the HO2S's heat up and throw the PCM into closed loop operation.

 

[mailboxman]

update

checked again today for vacuum leaks--negative --i checked the throttle idle screw and backed it out until it was not touching, and then went in about three quarters of a turn so that plate doesnt hang up--didnt help--I am banking on the new motorcraft tps on correcting my problem--

 

[mailboxman]

I should be recieving my new TPS today and will post results--but I noticed today that when I am sitting in idle, sometimes the idle goes down when I press on the brake?? I checked the vacuum line to the brake booster really good for any signs of leakage but maybe I will have to check it again???? If it were leaking vacuum there--wouldnt the idle go up when applying the brakes??

 

[mailboxman]

Welcome to my World

Installed new tps last nite and no change!! Maybe a little worse!!! Idle now seems to hang a little higher on startup (2000rpm) and also between shifts--I went to auto parts and bought a new pcv valve thinking this was the only thing left--once again no difference!!! Looks like I am going to have to take it somewhere unless I pull the intakes off and replace gaskets??? Must be a vacuum leak--I also noticed this morning that the idle seems to be hunting a little now also where before it was pretty steady

cold startup idle goes to 2000 rpm
after about a minute goes to 1500 rpm
after warmup goes to 1200 rpm

THIS SUCKS

 

[PlumCrazy]

This sounds exactly like what mine was doing. I replaced the IAC and TPS but it still did it. I even swapped the TB thinking maybe the spring wasnt strong enough the pull the throttle cable back. I slide the cable back and forth thinking maybe the it was sticky, but it seemed to be ok. I eventually took the cable off and lubed it up just for sh*ts and giggles, and it worked.

-plumcrazy

 

[mailboxman]

Thanks Plum Crazy but I already went over that with a fine tooth comb and no cable hangup

Can someone answer me this--i replaced the pcv valve last nite also and it was different from the one I took out--the original motocraft that was in there had a straight pipe sticking up that goes into the intake through a short rubber elbow--the one they sold me has two vacuum nipples with a plug to plug the small nipple on top if not needed--so i plugged it--I noticed that both pcv valves are sucking full force at idle??? I thought they were supposed to open up as your vacuum goes down and only work when you are accelerating??? Mine is definitely sucking straight vacuum at idle--I took it off at lunch today and put black tape over the inlet on the pcv valve to block it off (temporary) and my idle is perfect!!!!!!!!!!! WTF????????????? is the pcv supposed to suck vacuum at idle??? Is the new pcv valve they sold me supposed to have a vacuum lone connected to the top nipple to close it at high vacuum???? did someone replace the pcv in the past with the wrong one?????

 

[PlumCrazy]

I work at an Advance Auto, The PCV valves come with extra ports and plugs so they can fit more than one make/model. The extra port just needs to be plugged.

 

[PlumCrazy]

The PCV valve is more of a baffle than a valve, it keeps straight oil from being sucked into the intake. If the idle drops when you plug it, then it means you probably have a vacuum leak somewhere else.

-plumcrazy

 

[mailboxman]

Thanks Plum Crazy--I have checked for vacuum leaks at least 10 times now and cannot find one--I will look again tonight--maybe I need to disconnect all vacuum lines and plug them up?? It seems the 4.0 has a lot of manifold leaking issues--i sprayed so much carb cleaner around the intake I'm suprised it doesnt lift the paint--If anyone has more suggestions on the vacuum leaking i would love to hear them--with the pcv blocked my idle seems good--right around 700 rpm warm--i dont know how it is going to act cold??? I will put the vacuum gauge on and post back

thanks to all once again.

 

[mailboxman]

OK Guys--blocked all vacuum ports coming off the intake and plugged my vacuum guage in--pulling a steady 20 on the guage--the idle is acceptable with the pcv valve removed and plugged--but as soon as i put the pcv valve on my idle climbs back to 1200rpm---once again, as soon as I disconnect the iac my idle goes down to 600---this is blowin my mind!!! I was never able to do the KOER test correctly--i will study up on this and give it a try---maybe it will unleash some secrets

 

[TrexMex]

Going back to the TPS....

You wrote earlier on the post you reset the TPS to 0.96v.. found this...

http://www.fordfuelinjection.com/?p=30

Maybe setting it up to the lowest value (0.61v) in the tolerance range could help?

 

[Ranger44]

I doubt it's the TPS.

Did you ever retorque the lower intake manifold? They tend to loosen and cause.....vacuum leaks.

How are you checking for vacuum leaks?

 

[mailboxman]

tps voltage key on engine off at .99

i checked vacuum with engine running at idle warm (somewheres in the vicinity of 1200rpm) and sprayed down all hoses (vacuum) brake booster, intake manifold, pretty much everything and everywhere around the intake-tried carb cleaner, brake cleaner, maf cleaner, and even in desperation the other nite i tried silicone spray because it was the only thing i had left in a spray can-never made an inkling of difference on the idle speed---

Do you think it still looks like a vacuum leak??? even with the iac disconnected and engine running at 600 +- rpm, my vacuum is still pulling 20 on the gauge????

Once again, I have never mastered the key on engine running test and i have been studying exactly how to do this and will attempt this weekend--once again, no cel -- since Tuesday night I have been running with the pcv valve blocked and the truck is not down to the correct idle speed, but it is not racing like it does with the pcv plugged in--i also realize this is not good for the motor not venting the pcv but hopefully this is only temporary.

 

[TrexMex]

OK long shot but might be worth the try....

Would you have access to another EEC (a friend's maybe)? It might be that your EEC is screwed... Try swapping them just to check. This comes from you saying that when you unplugged your EEC and plugged it back it worked fine until you pressed the gas pedal...

EDIT: One other thing that I didn't see in your posts is if you checked the Throttle Body valve to be shut at idle... I know, stupid and obvious, but the simplest details can be overlooked when these types of things get into one's nerves....

 

[mailboxman]

thanks Trex Mex--I dont know anybody with a truck this old (1994) so swapping id gonna be tough--i did check my throttle and throttle stops and it is not in there either--i have been studying koeo and koer tests and performed at lunch time today--please look and comment
koeo
522 (O) Park/Neutral Position (PNP) or Clutch Pedal Position (CPP) circuit fault – PNP
157 (R,M) Mass Air Flow signal is/was low or grounded – MAF
koer
411 (R) Idle speed system not controlling idle properly (generally idle too high) - ISC
412 (R) Idle speed system not controlling idle properly (generally idle too low) - ISC

the only thing that bothers me with the maf is that this code should not show up on the koeo test?? The codes say it is a memory or a run test????? Although the only freaking thing I havent changed is the maf--what does everybody think??? Is there another test I can do on the Maf?? I cleaned it twice so it aint dirty