I have a 1994 Ford Ranger with 4.0 V6 Automatic. The problem is when it idles it idles low and surges up/down and pushes a very small amount of black smoke puffs and smells like gas. I have installed new coil, new wires, new plugs, new ect, new crankshaft position sensor, and new maf. It has new intake manifold, new injectors, new alternator and it still does the exact same thing. Nothing is phasing it. I ran the key on/engineoff test and got egr codes and a map sensor code, then ran the engine running test and got 998 and 126 code. The 998 code says that its basically a hard fault/ have no idea. I do know this is a donor engine out of another year not sure what year, but i know when i ordered the coolant temp sensor the only ones that would plug into it are the years 1990-1993. Now heres my other question, why would the computer give me a map sensor code when truck doesnt have a map sensor? It has MAF sensor, and why egr codes? The truck doesnt have egr and never came with it. I do know I've unhooked battery and replaced the maf and its like it doesnt even recognize it? Could it be the ecm/computer bad or needs flashed?

 

oh I think I have to disagree with you,,,, that truck does have a EGR system if its a 94,,, and I would read the codes again and see if you get the same results

 

Oh and it sounds like you have just been throwing parts at it,, so if you want to throw anther part at it try the throttle position sensor,,, sounds like it is the only thing you have not tried,,, but it is best to read the codes again and see if you get the same results

 

I did and same codes

 

And it's a donor engine, and doesn't have egr system I promise

 

Welcome to FTE.
Some unknowns may be confusing things & you may have more than one problem.
Why was the engine replaced, is this a flood vehicle?
Did it originally have a 4.0L in it?
Do you know if this is the OEM computer, or if it too has been replaced?
Are the replacement parts after market, reman, or OEM?
Are you using a OBD-1 code reader, or using a hook up to activate the CEL, test lamp, or analog meter to flash the codes?
The puffs of black smoke suggest that the fuel trim is corrupt rich for some reason & if disconnecting the MAF sensor has no effect, I'd put it on the suspect list, especially if it's a reman.
How does your scan tool show the fuel trim & O2 sensor readings to be?
Is the IAC reconnected & is it functioning?