Ack!... I'm at a loss. Read many posts on this board and even after getting codes, this problem is intermittent. Here goes:
Truck - 1990 F150 XLT Supercab w/302 V8 was running wonderful, then noticed check engine light came on, at same time, the automatic transmission was shifting very suddenly and hard, not smoothly. Also, idle speed dropped to 500 rpm, with occasional stalls. Note, this all happened at once. OK, I had let the truck set a couple weeks prior to getting around to diagnosing, jumped in, started and ran great all weekend, no problem, check engine light was out. This was strange. So, I started looking for a problem that now wasn't there, checked hoses, removed connections, removed relays and voila (I thought) ECM relay was corroded. Cleaned up and still ran good thru weekend. Thought problem was gone. Monday morning, pukey running again and check engine light back. All same symptoms. Took to Autozone and codes 063 and 032 were given. Drove home and let sit another week. Next weekend, started and run fine, no problems,.. I think OK>>> maybe the ECM relay needs replaced, I did, and still runs good. Monday rolls around, start in morning and blech...Check engine light back to haunt me and running pukey again. Oh... I really don't believe it is the TPS or the EGR since the problem is strangely erratic. However, I am willing to listen to any suggestions at this point.

 

sounds like a TPS to me. I had the same problem. Check engine light would come on and the truck would run good, then the check engine light would go out and idle real high. Then jerk when coasting to a stop light, stalling. I finally replaced the TPS and now the truck runs perfectly.

 

The thing that bothers me, or that I find most odd, is the transmission acting the way it did. When check engine light is on, transmission shifting is abrupt, very noticebly, and NOT smooth. How can this be related to the TPS?? Is this just a 'Limp along' mode that the computer is in?

 

Is it an electronic transmission? If so, throttle position plays a big role in determining shift characteristics. You can check your tps with a volt meter and see if it is acting erratically, or shorting out internally. The volt meter should smoothly progress up from about .9V at idle to about 4.8V at full throttle. If the voltage jumps around, or the minimum voltage is below ~.7V or so, then I'd replace the TPS. I would also check the condition of the SIGRTN (black) wire from both the TPS and the EVP as well as the reference voltage to both of those sensors (orange wire, should be 5V). I'd also go through and make sure the grounds are good.

 

That's what I thought also. When my truck started acting funny this girl that worked at Napa told me to change the TPS. Instead I replaced the coil, plug wires, fuel filter, plugs, air bypass valve. About $400.00 later, I finally checked the codes and they were 23, 33, 72, changed the TPS. My truck runs better than it has in 5 years. I couldn't figure out the transmission jerking when coasting. I think it was the computer adjusting the injectors to compensate for the erroneous throttle position. Hope this helps

 

you can check the TPS, with key on you check the voltage coming from the TPS. There is a procedure in the Haynes manual. it should be .5 to 1 volt closed. 4.0 to 5.0 volts full open

 

Thanks all! Checked the TPS voltage, jumped some just off idle, replaced, and seems to be the fix. Will post an update if it lasts longer than a week. Great Forum!