Allright, I have read through previous posts, and I know that this is a common problem, so here goes. Truck is a 1990 Crew Cab F350 4x4 351W C6 trans. I have no Cats, Air pump is disabled, vacuum readings are steady at 18-20" at Idle checked at the vacuum tree on the upper intake manifold. I have checked and have no vacuum leaks that i can find. I have replaced both upper and lower intake manifold gaskets, while doing this, I cleaned out the upper and lower manifold and the IAC valve. Parts that have been replaced: TPS, adjusted properly, O2 sensor, ECT, IAT, Fuel Pump, Vaccuum Modulator valve on the transmission, pickup(stator), Ignition Control Module, alternator, Fuel Pressure regulator. Mods done to the truck: removed AIR lines/ plugged, cats removed. The truck has an idle surge after approx 10-15minutes of idling. The truck normally idles between 900-1000rpm. when it surges, it will drop in rpm to 500 and then it catches itself and revs back up to 900-1000rpm, never goes any higher. After it does this a couple of times, it dies. I just got done removing the vaccuum line to the EGR valve and plugging it. This kept the truck from dying, but the truck still occassionally surges. The most recent code retrieved from the computer was a code 29 in continuos memory vehicle speed sensor voltage too low. I don't think that the computer is bad, because its trying to control the idle, also the fuel pumps only run for about 2 seconds when the truck is first started, however when the truck shuts down I notice that the fuel pump seems to run for a while after the key is shut off. Any Ideas are appreciated. Fuel pressure is about 44psi at the regulator. The Bleed down rate appears to be within standards of the Haynes Manual.

 

i went through this problem a few months ago on my partners truck. it ended up being a loose wire connection in the tps connector. it took me 3 weeks to find it.

 

I replaced the tps, when I did, I checked it with a voltmeter, and showed fine. Any more ideas?

 

After you have tried everything, but before you go nuts, you could try this. It is available elsewhere cheaper, and some people have had very good results with this kit.
Good Luck Frank

http://mustang.c-f-m.com/index.asp?P...ROD&ProdID=649

 

it was not the tps. it was a loose connection in the wires going to the tps.
we did the same thing. replaced the tps and it still ran like crap. as i was under the hood trying to figure out what to do next, i started grabbing wires at there connections and wiggling them. then i grabbed the tps connector, the truck smoothed out. move it another way, and it ran like crap again.
i got another connector out of a junker, and replaced the connector, and the truck has been running fine with the original tps for 4 months now.

 

Well I have finally figured out the issue, it was not the wiring harness, the computer shot craps on me while I was out and about, first when I turned the wheels sharply, it would die, then when it got hot, it was hard to start. I got the truck to auto zone, took the starter off to test it, starter was fine, replaced solenoid, and then truck would crank, act like it wanted to start, and then immediately die, I thought that something was up when the check engine light would not light up when the key was switched on. I couldn't read any codes at all, then when I turned the key to crank the engine, the check engine light would flicker, the engine would try to start and the truck would immediately die. I checked all wiring to the computer, and it checked out. Everyone tells you that these Ford Computers rarely die, this is the 2nd ford truck i've owned and in both trucks the computers have died. I think its crap that there is no direct way to test these computers, you have to eliminate every other possibility first, before you can figure out that the computer is bad.

 

break out boxes are a God send dealing with those ECM's!!!