I went to start the truck and take garbage off this morning and the truck would not idle at all. I thought at first it was a fuel pressure issue (had it happen in the past) and pressure was fine. I pulled the code and got a code 63 (TPS voltage too low). I grabbed the VOM meter and back-probed the signal and reference wires and found it to be .68 volts (within spec from the info on fordfuelinjection.com). When I opened the throttle body it would only get to 2.8 volts at WOT. Would this cause my idling issue with it having that low of a voltage? IAC works (checked this after the fuel pressure) and all of the vacuum lines are snug and no leaks. Would hate to buy a new TPS and have the same issue happen again.

 

did you check the phsyical parts of the IAC?

Lots of times TPS's get wore out, but it should idle fine with a bad tps.

I'd pull the IAC and clean it. TPS's are 30-40 dollars if i remember. and a 10 min install. Well, probably 30 for others. I've replaced 2, I got it down. =) Though, it took about 20 the last time. had a 10 min beer break.

What i do when i test a TPS is pull it off, and hook up an ohm meter to it, and make sure the resisitance climbs evenly without droping.
I do it with a screw driver.

 

IAC was cleaned out last month. I'll try it with the Ohm scale and see what happens with it in the morning if it isn't raining and I beat the wife home from work....

 

OK, this is what I've found out this morning diagnosing it. I backprobed the wires and had .86V with the throttle body in the closed/ idle position and 3.77V at WOT. I took an analog multimeter and set it to ohms to see if the resistance would be linear. No issues there (was linear). What gets me stumped is everything is showing to spec except for WOT voltage. I'm going to go ahead and swap it out to see if it solves the issue with it idling. If not, I have a good Edelbrock/ Holley combo on my Mustang that might get another home.....

 

You have to turn that TPS really slow to notice any changes.
It's really touchy.
If you turn it to fast you will never notice a flat spot.

I've cleaned IAC's before and still had them operate incorrectly. I had to replace mine anyways.

Also you could check the FPR, and see if your having fuel issues.

 

I turned it really slow and didn't see any flat spots. I borrowed another IAC valve and it still has the same symptoms. FPR was already changed out last month and fuel pressure is good. Going to try a few more things before work and see what happens.....

 

The only other suggestions i have is that the timeing has slightly gone off, or the timeing chain has stretched a bit. Which makes no sence, i know. but. It happens.

There is the controll module on the distributor that causes wierd problems. not suer if that would have any effect on it.

 

New TPS is going on in the morning to see if it rectifies the issue. Hopefully it does.......

 

Just put on the new TPS and it didn't fix the problem!!!! Ran the codes again and everything came back as a code 11 (system OK). I'm about to my wits end chasing this issue (going to try another distributor in the morning for laughs) and if I can't get it fixed, screw it. I'll change it over to a carb setup and then it will run...

 

Try holding the gas pedal to the floor and starting it.
The truck shouldn't fire at all. It shuts the injectors off.

If it doesn't start.
Then try resetting the trucks computer by disconecting the battery for a bit.

*shrugs*

 

Okay, spent the weekend hitting this turck hard and here is what I've done so far without success:

Changed TPS to new one
Checked IAC and tried another good one
Changed distributor
Reset computer

After all of this I pulled the codes and got a code 11 (system OK). Now here is the kicker. IF I pull a vacuum line off (pulled the one from the cruise control servo, the truck will idle fine!!! it will even do this with the IAC plugged in or not plugged in (but I can hear the IAC working or sucking in the air). However, if I take my thumb and cover the vacuum line it will stall out or idle very rough. I checkd the IAC ports on the valve and the throttle body and thy are clear of any debris. Does anyone know what voltage should be going to the IAC valve motor (read between 12 and 13 volts)??? Might have to pull the uper intake off and see if there is anything in there.....

 

After reading in my shop manual and thinking about it last night at work, I'm gonna try the MAP sensor and see if that is the problem considering the symptoms that I had diagnosed in a previous post.......Anyone know how or where to take one to get tested?

 

Check your EGR, might be stuck open a little.

 

You can check the output of the MAP sensor using a frequency scale (Hz) on a multimeter, or somehow use a 6 cylinder tachometer, but I've never tried that. If you check voltage, you will notice that the output voltage will be 2.5V no matter how much vacuum you supply to the sensor. I don't know the frequency ranges off hand, but a repair manual should list the frequencies for various manifold pressures (vacuums).

 

Thanks. Will take a stab at this


As far as the EGR and anything emission related (cat, EGR, smog pump) those parts are LOOOOOOOONNNNNNNNG gone.......