Hi all. I have an issue with my 91 f250 351w efi. It started last week when I noticed a slight stumble off idle. Then it went into the shop for some suspension work. When I got it out and got it home as I pulled into the driveway it sputtered and died as I was putting it into reverse (5spd manual btw). It started back up ok but with a pronounced rough idle. I moved it to where it needed to go and let it sit idling for a few min. It was still idling kinda rough then a couple of times it just died. One time it took a couple tries to get it started again. It was almost as if it was loaded up/flooded. Once I got it going again it would go from idling without a skip to having to have my foot in it just to keep it going. A couple times when I let my foot off it would almost come down to idle then race up to 2k rpm then drop down to a very rough 750 rpm idle. Now just before it went in the shop I did a tune up on it (plugs wires cap rotor) try to get the idle to smoothe out a bit. It ran ok but no difference in the idle. It was t until I got it back from the shop that it started doing this. I'll be doing the fuel filter tonight and probably a test on the tps. Besides taking the tank down and checking for tank sludge, testing the iac, or looking for vac leaks is there anything else anybody could suggest? Any known issues that I might be overlooking? Thanks in advance

 

There is a good possibility something was moved or possibly disconnected during the suspension work. Did they work on the front or rear suspension?

 

They did left ball joints, left inner tie rod, ebrake cables and a wheel seal on the left rear. I've heard some rumblings about cheap plug wires cross firing if they're no routed correctly. I wasn't all that careful in the routing. Does that idea have some merit?

 

The most important wires to keep from running parallel with one another are #s 7 &8.
What you might consider is getting a fuel pressure gauge and getting a reading of your fuel pressure on the fuel rail.
Did you check for any large vacuum leaks?
We need to start someplace and fuel pressure is as good a place as any.
How did you make out with changing the fuel filter ? When you go to remove the old filter you need to relieve the pressure in the fuel line first or you will get a fuel bath.
You can do this by pulling the fuel pump fuse or relay while the engine is running so it runs out of fuel and the pressure in the line will be gone. Then remove the filter from the holder and the white nylon retainers that hold the line to the filter. If you can turn the old filter to drain it out the inlet end and see what if anything comes out. You could get water, gasoline, dirt or rust. After installing the replacement filter turn the key on and off a few times to prime the line and fill the new filter. You must always go under the vehicle when done to check for any leaks!

 

I did the fuel filter and no change (no surprise there as there wasn't much in it). Took the tb off and tested the tps and it was all over the place both on voltage and resistance. Replaced the tps and voila! That cured most of it. Now my only problem is a slight stumble off idle. Also I noticed that my coolant was really low so I added some and it got really frothy like the head on a freshly poured beer. I pulled the dipstick and no milk. There's no scum in the radiator. Could it just be that because it was so low the pump churned up some froth when it came across the air pockets? I'll probably do a flush sometime soon.