4.6 liter when engine is cold idles normally. When engine warms up idles rough, and stalls. I have to keep rpm at 1000 or above with pedal. Upon acceleration engine operates normally, and smoothly. Has check engine light, however the code reader output is not working. Guy at AutoZone says fuse is probably blown for obd . I have searched and not found a blown fuse. I have cleaned maf. New air filter. I am thinking maybe iac malfunction, or maybe o2 sensor and cat. Any help or suggestions will be appreciated.

 

Did you check the fuses both ,inside the vehicle and under the hood in the engine compartment.

Without being able to get the code for direction, a lot of tests and checks would have to be done and can involve a lot of time and $$$.

Just for the heck of it,
do you have any add on items not factory on your vehicle? Like alarm, audio etc.

 

I did but didn't find any bad fuses. Just got this van used. And apparently it did at one time have some sort of alarm and some other equipment wired into it. The thing is the fuse that is supposed to power up OBD, according to the fuse box diagram. There's no fuse there and there's nothing there to hold a fuse. So I'm worried that somebody has done some kind of weird wiring in there.

 

And what I mean is the space where the fuses supposed to go when you try to put the fuse in it doesn't stay in it's like there's no prongs for it to grab onto

 

Because we don't know where, or what wiring, was or might have been tapped into , Just about anything is possible.

Removing the source of power most likely will not produce the same result as "completely disconnecting " an add on from a circuit. In other words , remove it !

What may be happening,
As long as the engine temp is below a certain point and the oxygen sensors are not hot enough to supply info to the ECM,the base programming is allowing the engine to run satisfactorily.. However, as soon as conditions are met and the computer takes over with the info supplied by the various sensors idle is affected.
There may be more than one problem as you have already noticed.

 

I found a blown fuse and replaced it. Had the codes pulled. I used propane to check for vacuum leaks but didn't find anything.

 

We usually try not to leave any dangling pieces, ,,,,so,,,,,,,,,, what was the blown fuse protecting that you replaced?

Usually if there is a vacuum leak, idle can be affected,but as RPM is increased any roughness will disappear.

The intent is to determine what info is going to the PCM and determine which is not correct or rational. This is usually done with a scan tool that can provide what is called "Data Stream" and we go from there.

 

Although codes pulled suggested a possible vacuum leak. I found no vacuum leak. I had a spare maf sensor. On a whim I changed it out, and Bam problem solved. Runs like a top now.

 

With that kind of luck, how about a shot at the lottery, you never know !!

 

Thanks for the help.