My 1993 f150 is running poorly. The truck has 144k on it's now getting around 7 miles to the gallon. It's sputtering during normal driving conditions and will die when idling at a light. Since this problem started around 1000 miles ago I've done a tuneup on it (plugs, wires, cap, rotar, o2 sensor). Still no difference. I pulled some codes with the engine running -

12 Idle Speed Control motor or Air Bypass not controlling idle properly (generally idle too low)
42 (R) System rich
(M) System was rich for 15 seconds or more (no HO2S switching)

What's the next step?

 

I would say to replace your IAC motor. If the fuel pump is sending normal amounts of fuel but the IAC motor is allowing a smaller than normal amount of air, the thing is gonna run like a pig, such as you are seeing now. I would start with your IAC motor.

 

* What kind of shape is your MAF sensor in? If dirty, be sure to use the proper cleaner - regular carb cleaner will destroy it.
* Have you checked the base timing?
* Injectors fouled, not atomizing fuel properly?
* Validated correct plug wiring with secure connections after tune-up - no crossed wires or the like?
* Good bluish spark, versus a weak orange or yellow?
* EGR valve operating properly, not stuck open? Although this should throw a code.

Some of the above may seem trivial - but I always fall back to the philosophy that if I can't figure out what it is, then back into the problem by figuring out what it's not. For a rich condition, looking at whether one has too much fuel, not enough air, or a faulty ignition.

Welcome to the site, good luck, and keep us posted!

 

I just had a very similar problem with my 1992 5.0, and I put a new EGR valve on and it fixed it immediately. For some reason, the check engine light would come on and go back off, then it would start dying, but other than the knocking, no more dying or check engine light! =)

 

Oh, and I had the same codes as well, so that very well may be the problem.