I have a 94 f150 with 5.8l and e40d tranny.the engine cold idles at around 1400 rpm and warm idles at 1800 rpm.i've replaced the tps,iac valve,map sensor,act sensor and the egr position sensor.the engine runs great as well as tranny other than the fast idling.cant find any vacuum leaks.plugging the pcv valve air port on the plenum helps a little but i dont think it is a factor.could the pcm be the culprit here?a while back, the digital odometer just went out while i was driving down the road but came back on minutes later.this past weekend it went out while it was running in the driveway but came back on minutes later.if it is the pcm,will the mileage get converted over to a new one if i replace it??i am completely out of ideas or theories so could someone please point me in the right direction.

 

I am not an expert but I would have said a bad TPS but you have already replaced that. I would suggest you go to fordfuelinjection.com and use the info there to check the voltage at the TPS and also good instructions there for pulling any trouble codes (if you don`t have a code reader).

 

The mileage is not kept in the PCM computer, it is kept in the PSOM computer.
The PCM computer has nothing to do with the odometer.

Run your codes and get back with us.
Let us know where the code is from also (KOEO, CM or KOER).

 

I ran a test using the innova code reader and heres what i got.

Koeo test - all passed

koer test

311 - thermactor air system fault
213 - spout circuit open
411 - cant control rpm during koer low rpm check
538 - invalid cylinder balance test due to throttle movement

just a thought but could the timing be off causing this? I've been tinkering with this idea.i was going to check the base timing but my harmonic balancer is pretty much unreadable so finding tdc has been difficult.i noticed if you turn the distributor with the ignition key on, the fuel pump will cut on at a certain place which seems to be the sweet spot as far as it running but this is where it idles at 1800 rpm.i turned it ccw which helped bring the idle down to around 1200 rpm but performance seemed to suffer.also, i cant find the spout connector to disconnect to even do a base timing check.could the distributor maybe be a couple teeth off and am i even on the right track?the timing issue seems to be the only thing that even makes a difference.by the way,the check engine light hasnt been on at all during this whole ordeal.

 

You should not move the distributor if it runs without a timing light on it.
Make sure the SPOUT jumper is installed, photo below.
Also sounds like you have a bad IAC valve and you need to clean it or better yet replace it.
Then get a timing light and make sure the SPOUT is out and set the timing at 10 degrees BTDC. Replace the SPOUT and make sure the timing has moved some off of 10 degrees.

First you will need to lay under the front of the engine and with sand paper clean and remark your damper at 10 degrees BTDC.

After you do this and you still have problems after clearing the codes and rerunning the codes report back and we will help some more.
Also if this fixes everything let us know that too.




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No obstruction at throttle plates,carbon?

 

I went ahead and replaced the balancer to get some readable marks.unplugged the spout.set timing to 10 deg btdc.reinstalled spout and timing moved to 12 to 16 deg btdc.engine is idling at around 1500 rpm hot.ran codes again and now only get the 311 and 411 koer codes.i had already replaced the iac valve.should the rubber plunger in the valve be completely seated when its cold?i noticed that it is raised a little less than 1/4 inch.just wondering if the valve is bad from the parts store.any other suggestions??

 

Unplug the IAC valve when it is running and see where the idle drops to.

 

Its been awhile since my last post as I havent made any progress since.Cant find any vacuum leaks,replaced plenum gasket,replaced every sensor under the hood.Voltage from TPS is at about .9 volts and increases smoothly as throttle opens.Throttle plates open smoothly with no obstructions.The only thing I can find is that the voltage to the IAC with KOEO is 12 volts.All info I have found says it should be 9 to 10.5 volts.I thought maybe the PCM was the culprit so I tried a new one and it was still sending 12 volts.Unplugging the IAC doesnt change the idle either.Idle is currently at 1500 rpms and will drop to 1000 rpm when put into gear.Also, I thought maybe the timing would be an issue.I believe it is supposed to be 8-10 degrees BTDC but that would be on an engine idling like it is supposed to which I'm guessing would be around 800 rpm.Any suggestions would be deeply appreciated as I am very close to just getting rid of it and getting a newer one if i cant solve this problem.

 

If you took the IAC Motor plug loose and it didnt change the idle..Check the idle adjust screw or a binding throttle cable or linkage..Have you replaced the IAC Motor,if not try running the truck at idle and tap the top of valve with a hammer,may be sticking...

 

The PCM does not send the 12 Volts to the IAC, the PCM Power Relay does and it is controlled by the ignition switch.

 

The IAC is controlled by the PCM.The Positive wire is controlled by the ignition switch..The Pcm controls the ground side of the IAC.If you would like i can provide wiring diagrams..

 

So is that to say that either there is a bad relay or a bad ignition switch?If so,which relay or relays would it be in the power distribution box on the fender?

 

There is nothing wrong with the relays if you have 12 volts at the red wire going to all the solenoids and injectors.
The 12 volts on the red wire is switched on by the PCM Power Relay in the engine compartment fuse box.

 

Did you buy the truck with this problem?..You need to check the Voltage signal from the TPS to the PCM..at an idle it should be less than 1 volt... The reading should be,i believe from .6 to 1 volt. If it is higher then it is likely someone has adjusted the idle.The PCM uses the readings from basically 3 sensors to adjust the idle..The TPS , MAF and the ECT sensors.If the idle screw has been adjusted ,you can get the symptoms you are having.I am not saying the PCM is not bad,but i have a small repair shop and over 15 years i can count on probablly one hand how many PCM,S were acctualy bad..Do you have a repair manual? If so do the checks for the TPS and go from there. I understand this is frustrating but you have to Eliminate the Sensors (by using the data you retrieve from them). On the TPS you have three wires 1.Voltage reference , 2.Ground , 3. Signal Return...The PCM sends a 5volt Reference through the Voltage reference wire..The TPS is set at an idle to return .5 to1 volt back to the PCM (the pcm recognizes this reading as basically a closed throttle and can adjust the IAC Valve accordingly.As you open the throttle more voltage flows through the sensor back to the PCM.The Pcm recognizes this as throttle movement and along with input from the other sensors,adjusts the engine parameters accordingly. Use your book for the wire colors and backprobe the signal return and ground wire..With key on and engine off you should get between .5 and 1 volt ..any higher and the idle will be high..Either the TPS is faulty , installed incorrectly or the idle screw has been tampered with or sticking throttle plate shaft..Maybe i babbled on but i hope this helps..