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My idle goes from smooth as silk to very high then so low it dies,ive replaced the tps and the idle air control valve,ive checked with volt meter the wires and all checks out good but the return (b/w) wire. From what I understand with the meter on ohms its supposed to register less than 2.0, mine registered 0.01,is this abnormally low and could this be my problem?
It is not uncommon to have a bad TPS where the resistance drops to 0 (or close to 0) during movement (rotation) of the TPS shaft. This happens because the contact inside the TPS (a potentiometer) wears/rides in a single spot more often - meaning it doesn't wear evenly across the entire TPS range because the throttle spends most of its time in a narrow range of possible positions (like 1500 to 2500 rpm). Then as you test the TPS (with ohmmeter or reading voltage while rotating the throttle) you see something like 10 ohms- 20 ohms - 30 ohms - 0 ohms - 50 ohms - 60 ohms - etc. If you don't have a even variation of meter readings while rotating through the TPS range, then the TPS is bad.
I watched a video on YouTube of a man doing this and I followed his procedure precisely and there was no hickkup anywhere in the range as I measured that the only thing that didn't check out with the return wire as I had stated,could I possibly have a bad connection in the return wire the black-and-white one
The signal return and ground are the same thing. That is why you got such a low reading, the lower the reading the better. They just don't want it to get above 2 ohms where they consider it a poor connection to ground.
When does the truck act up? Only after it warms up or during warm up? Have you set the idle speed yet? Unplug the idle air control connector while it's running and see how it idles. If it dies, turn the idle screw in a little bit till it just barely idles. If it is idling fast with the idle control unplugged, then turn the screw back till it just barely idles, but it doesn't quit either. Do all this after it is fully warmed up. After you adjust it, give it a day or so to get itself re-adjusted. It takes a little bit.
Its a automatic trans, I've tried the code check, counting the flashes and if I did it it correctly it was something to do with the EGR valve, it hadn't been plugged in from what seemed like years from PO and it was stuck closed, I cleaned it and checked it and supplied vacuum, the engine ran horribly then died, checked the electrical signals and DPFE sensor which was supposed to be at least 100 ohms but was only 46,changed that and the results were the same so Im back at square one. I checked the TPS with volt meter, ran through the throttle and it climbed and dropped back as it should, as far as vacuum leaks I hooked up smoke machine and there was a small puff coming from where TPS was mounted,(looked like it took an O ring) so I placed an O ring on it but nothing changed, very frustrating as I stated whether startup or engine temp it idles smooth as silk to going absolutely berserk and everything in between,sitting idle in park with the a/c on a few minutes will trigger the idle to skyrocket,come back down run crappy and die,come out later and it runs great-I know this is a lot to take in but any more ideas?
Is the throttle body clean and is the Idle Air Control (IAC) clean?
These tend to get "coked up" because the PCV dumps in front. There also a TSB out on a IAC fix related to TB coking. It's TSB 91-25-7 IAC By-Pass.
The TPS measurement I was referring to is the signal output to the ECA/Computer, Pin # 47.
Measure the Dark Green wire with Light Green stripe (DG/LG), to ground.
(Might be easier to stick some pins into the back-side of the connector.)
Do this at closed throttle and then at WOT. Voltage range is approx. 1-5vdc
Also Measure the Reference Voltage on the TPS - Orange/White wire to ground, dc volt
I've tried the code check, counting the flashes and if I did it it correctly it was something to do with the EGR valve, it hadn't been plugged in from what seemed like years from PO and it was stuck closed, I cleaned it and checked it and supplied vacuum, the engine ran horribly then died, checked the electrical signals and DPFE sensor which was supposed to be at least 100 ohms but was only 46,changed that and the results were the same so Im back at square one.
I know this is a lot to take in but any more ideas?
Loads of Ideas, just going step by step.....
The ECA does not apply vacuum to the EGR-Valve at Idle or during Fast Acceleration. So your test was was successful in the fact you opened and closed your valve. But, you computer would never open the valve at Idle, because your engine may die.
You MAP sensor could be the cause of your erratic Idle.
Do you have a Frequency setting on your meter?
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) Continuous Codes =
KOER - (R) Self-Test Codes =
I would quit looking at the tps. When it's idling crappy you are not touching the throttle correct?
I would not worry about the egr valve. Leave it disconnected. All it will do is cause the computer to be a little conservative on the timing once it realizes it's not working. As long as it's not leaking and can't open, it should not cause a problem.
One thing you can try; While it's idling and behaving itself, start grabbing and pulling on various places in the wiring harness. See if that causes it to act up.
There is a small ground wire coming off the negative of the battery. It goes to a small connector and then goes in the harness. Check this connector and this wire for corrosion. I checked the one on my truck the other day, it looked good but while it was running I unplugged it. Bam! it died. That really is a important wire going to the negative battery terminal.
Go in a lightly wiggle your ignition key. Does that cause it to act up?
Probably no one is watching this thread and crossing their fingers for a definetive cure for the OP's described symptoms than I. I have a 1986 F150 5.0LEFI w/AOD, owned since new. My truck has exhibited these symptoms, to a certain extent, for as long as I can remember. It still does. What I learned from my former neighbor, who was and still is a Ford Tech, was to keep the throttle bodies absolutely clean. Clean with very special attention given to the tiny slots in the photo below. Every time my truck gets to the point where the engine begins dying, I clean the slots again. I still get the fast idle, it still drops too low at times, but it quits dying on me.
That said, I hope everyone sticks with this thread long enough to solve the problem wholly, once and for all. I have done everything the OP has done and more to no avail. Thoroughly cleaning the TBs has always alleviated the symptoms to the point where they are bearable. Here's hoping that the OPs truck, and mine, are cured sooner rather than later. EDIT: Hey! Look who finally has a new FTE banner.
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