Hi! My husband and I have bought a nice 1994 V8 auto 302 f 150. It has 134,000 on it and I intend for it to be my horse trailer hauler. However, it has a strange problem. This problem doesn't show up until we have driven it 10 or more minutes. The engine revs unexpected, the control of the gas pedal doesn't seem to be there and then most times it finishes with a lurch. Usually this is done at all different speeds;local town driving or hwy speeds doesn't matter.
We have had it to the mechanic several times. They have so far done the following: tune up, transmission service, replaced the rotar button(was burned through), adjustment of timing, adjusted throttle pressure. We have no engine service light on, and it has passed its emissions test.
This is SUPER annoying and I don't feel I can pull a horse trailer with a truck that is lurching and surging and reving. Anybody got an idea of what this is and what it would take to fix it?

 

It sounds like the transmission is going into neutral, motor will rev then slam into gear? You said trans service, was this just a flush or did they replace the filter? The trans may be overheating, if the truck only has the radiator trans cooler these can stop working over time. Kind of the same reason why a lot of oder cars and trucks tend to overheat with the ac on or on a really hot day. Both motor and trans sides of the radiator can do this, but a lot less serface area is used for the trans. Usually when a transmission starts to act up it is already too late to act. Check on the filter, if it has been done I would add a large trans cooler (about $75 for kit), your going to want one anyway for towing with a 100k + truck. Make sure the cooler lines are getting hot, remember a trans's normal opperating temp is much higher than the motor, be careful.

 

Welcome to the site!

The Idle Air Control (IAC) solenoid and the Throttle Position Sensor (TPS) would have been my first guesses - except the 10 minute delay and no 'check engine' lamp moves them back in the probability of causes, for now.

The IAC for these model years has a tendency to gum up, causing idle speed problems. I suppose if it were going haywire at all engine speeds, could see some of the issues you describe, but I don't understand why it would repeatedly take 10 minutes to act up.

The TPS failure I experienced caused all sorts of bucking and snorting - but it was apparent from the get-go, and the computer flagged it with the 'check engine' lamp.

One thought is a vacuum leak somewhere. The only thing I can think of with the kind of delay described would be the EGR system. I recall one member finding the EGR tubing had a split in it, allowing fresh air instead of exhaust gas to be pulled in - upsetting the fuel:air ratio, causing RPM problems also. Perhaps one way to quickly check would be to unbolt the EGR valve from the intake plenum and blank it off, or another way might be to remove the tubing connector from the bottom of the valve and duct tape the valve inlet.

Good luck, and keep us posted.

 

ah, good point BC - wasn't even thinking about a tranny problem.

 

Sorry, I did not get back to those who posted answers. We had fun storms last night and no electricity.
Most everything you all said is greek to me. However, My husband may know more about what you are saying and you are giving us some directions to pursue. Thank you so much.
I have another question and my husband and I differ on this.
Is it better to take your car/truck to a dealer to get a diagnosis and then fix or to take it to the normal mechanic and let him fix things until it is figures out what is wrong? In other words will the dealer's mechanic get the right answer or do they fiddle around fixing stuff till they get it right too? We have been messing with this bucking thing since Nov 07
My husband is afraid they will cost thousands and then maybe fix it and it is a lot cheaper from the local guy (who up to this point hasn't fixed it.)
Is it wrong to go to the dealer get it diagnosed and then take it to the local (read cheaper) guys to do the fixing? And no, neither my husband nor I are mechanics. If it is a horse I can fix it but alas it is not.

 

I don't think the motor in a auto can rev in gear without it being a trans issue. A lot of times when a transmission starts to have trouble it will come out of gear at lower RPM's then slam back into gear when the motor revs up. Can you rev the motor while in D when the problem occures. If we can narrow your problem down a little you will also have a better idea on where to go and the cost.