Any help is greatly appreciated,

My 1988 F-350 started idling very high, over 3,500 rpm. I replaced the throttle position sensor and it ran great for a day. Then it started idling high again.
I then replaced the idle control valve and the map sensor. It didn't improve.
I took it to my garage and the mechanic, after running tests, said it was my TPS again.
He replaced it and it ran fine for a day or two.
I took it back and he replaced the idle control valve (yes, I had replaced it). That didn't fix it, so he pulled the computer and it had a small amount of water stain on the outside and thought we should replace it with a re-manufactured one, which I said okay to.
It ran fine for a couple of days, then started its high idle again.

When I took it back, he tested everything and said the TPS was bad again and replaced it.

I drove it for a few days. Now it is bucking and killing, instead of the high idle.

He says it is the TPS again and wants to replace it with an OEM TPS. He also isn't sure if something else is making the TPS go bad, or if we have been getting bad TPS's.
The one I replaced the first one with was from NAPA and the two they got were from Car Quest.

Does anyone have experience with something making TPS's going bad? Could they have all come from the same factory and gotten a bad batch?

Thanks for any help.

 

did you test the tps off the truck sounds like maybe the plug is bad

 

order your tps from advance auto.its boxed by BWD.they are stamped with FORD,reasonably priced and have a lifetime warranty.

 

So now, four years later, has anyone figured out why these sensors keep going bad? I've replaced both my TPS AND MAP sensors within the past year and a half and I just pulled a 634 TPS below minimum voltage and 126 MAP sensor above or below normal 2. cylinder identification circuit failure codes from my 1992 F-150 XLT 5.0 Auto RWD truck. The suggestion of a lifetime warrantied replacement is great but knowing the root of the failure would be the holy grail here. Thanks in advance for any help you can offer.

 

Well, first off, is this your problem? Sounds like electrical problem to me. I would check the TPS and be sure its not below spec, which is around .60 volts.

Next is to check 5volt reference voltage coming into the TPS and the MAP sensor. If you get erratic voltage, then this would be the problem. If neither sensors show a minimum of 4.75 volts and its erratic, then I would suspect bad capacitors in the PCM. Your 5volt reference signal is filters through the capacitors in it and they are failing more and more, due to age, heat and cold cycles, and voltage spikes. They have more than outlived their lifespan.

 

I agree 100% with timbersteel.

 

Agree with the above. Test the components first, then the power supply.

 

I'll have to get out there with a multimeter and check it out. Quick rookie question, is the PCM different than the ECU? And if the fault is in the PCM would replacing the MAP and TPS sensors make the engine run right for a little while and then stop again later or would the fault be in the PCM the whole time and swapping IT out make the MAP and TPS suddenly be putting out a signal the engine can use again? I guess what I'm saying is would a bad PCM cause premature failure of the other sensors or just a garbled reading of their signal?

 

PCM and ECU are the same term for computer.

Before going off the deep end check the sensors and the VREF signal. The only way I can see a computer could damage basically analog sensors is too high VREF signal.

 

PCM = Powertrain Control Module
EEC = Electronic Engine Controller
ECU = Electronic Control Unit
ECM = Electronic Control Module
ECA = Electronic Control Assembly

All of the above refer to the engine (and auto trans) computer as rla said. Ford uses the first two terms, the rest are various names you might hear at a parts store or other place.

 

Ahh ok, just making sure there wasn't a separate computer for the transmission/powertrain as in some vehicles. One of my old Eclipses had both an ECU and a TCU. I'll have to google around for the process to doing voltage tests on the MAP and TPS in my truck. Looks like a Cardone A1 remanufactured PCM, and motorcraft MAP and TPS sensors are going to run me around $405 shipped from Rockauto which if it will end the endless maintenance issues I've seemed to have the past three years will be well worth it. I love this truck and considering she's spent almost 25 years almost exclusively in Maine (not including the year she spent in San Diego and driving both ways pulling a trailer) she's really in awesome shape.

 

If you have 30 minutes to kill, then removing the PCM is a no brainer.

1st. Simply disconnect the negative battery cable, keep it from making any contact from the battery.

2nd. Get a few extension's, a swivel, and a 10mm socket. It's the size of the bolt that tightens and loosened the harness up to the PCM.

3rd. Remove the lower driver side kick panel where the E-Brake is located. You will have to remove a few screws on the bottom of the floor that meets the door, so the lower extended part of the lower kick panel can be removed.

4th. Remove the (2) 7mm screws holding the Hood Latch to the cab.

Once all that has been removed, you can bend the PCM retaining bracket down and remove the PCM.
Just be sure that you unscrew the bolt first and disconnect the harness.
Also, the 10mm bolt will NOT unscrew from the harness. It's not intended to, so don't fret it.

I did it in 10 minutes yesterday afternoon, looking for a water leak. Only difference is that my kick panel isn't installed.

 

On my '89 I was able to just get the 10mm bolt out with just a 3/8" rachet and reaching under the master cylinder. Few minutes and the computer was out.

I've been dealing with drivability issues and been changing parts on it. Right now mine takes 3-4 seconds to drop RPM when you try to shift. Ugh. Just gotta love 1980's computers.