1994 Ford Ranger XLT 3.0L rough idle problem.

[Jackson2]

I have a 1994 Ford Ranger XLT 3.0L 6cyl 4x4 with 140,000 miles that's been having an idle problem. When I first start the truck in the morning, the idle is very rough. It will shake quite hard and try to die. The truck seems to do fine after it has warmed up, or the problem isn't quite as noticable, there is a slight miss with it warmed up that isn't very noticable unless I'm listening really hard for it. I've also noticed a slight dead spot or hesitation in acceleration. So far, I've changed the distributor cap and rotor, put new plugs and plug wires on it, new pcv valve, new dpfe sensor, new vacuum regulator, new egr valve, cleaned the MAF sensor, cleaned the IAC valve, new coil, nothing I've done has seemed to help much at all. I suspected the MAF was not working, so I unplugged it and my truck really ran rough with it unplugged and I got the CEL with it unplugged. My CEL hasn't came on with the MAF plugged in. I ran my codes on it and all I got was a code 111, which is an all clear code. I've also tried running a couple of cans of fuel injector cleaner through it, all to no effect. Has anyone else had this problem and solved it? I would sure appreciate some advise here, I'm about at the end of any ideas.

 

[Earl43P]

Two seperate problems?

Try turning the key to Run for 2 seconds (listen to the fuel pump run) then back to Off.
turn back to Run, wait 2 seconds, THEN crank it over and let it idle. If that helps, you may need a new fuel pump or fuel filter because you are losing pressure (bleed down) when the truck is not running.

The second problem, I see you cleaned your IAC. That's good, now let's see if it's working. Idle the truck, fully warmed up, preferably with the AC on. Note the changes in idle rpm as the compressor cycles on/off. Now disconnect the IAC and see how those idle rpms change. It may even stall when the compressor kicks on. If you see no rpm change with the IAC disconnected, it is bad - replace it.

 

[Jackson2]

I actually bought a fuel filter this morning thinking the same thing about the fuel pressure. I'll try the fuel pump test as you suggested, that's an excellent idea

Unfortunatly, I don't have AC in my truck. I live in Montana and have very little need for it. I'll try unplugging the IAC with the truck warmed up and see what happens. Thanks for the suggestions!

 

[Jackson2]

May have found the problem!

I had previously check all of my vacuum lines on this truck two different times thinking this problem could be simply a vacuum leak. Not being able to get this out of my head, I decided to check my vacuum lines one last time, running my fingers down each line. On the vacuum line that comes out of the pcv valve, it runs right beside the alternator. The "hiss" that I thought was coming from my alternator was actually a hole in a vacuum line! I'm going to drive this for a couple of days to see if fixing this leak has solved my problem. Earl, thanks for your comment and I'll still check the IAC valve just to make sure it is working!