I need help because I am at a loss.

i have a 95 with a 5.8. Starts up strong then immediately starts struggling. Upon looking at the plugs it’s running very rich. The truck will bog down if I don’t nurse it. After about 5 minutes, it levels out and runs normal. But while it’s struggling it struggles to accelerate and will back fire. Will go if you floor it but you can still feel it hesitate as you push through it.

items changed:
Map
IAC
Coolant temp sensor
tps
ignition control module
fuel pressure regulator
checked for vacuum leaks
egr valve good
egr position sensor good
vaccum solenoid good.
oxygen sensor

im at a loss. Anyone dealt with this??

 

Fuel Injectors leaking? Do all of the spark plugs look the same?

 

All of the spark plugs look the same. So it’s running rich the whole time until it clears up

 

Check for fault codes, and remember to clear PCM of any codes after repairs are made.

 

As you are probably aware, the ECM tells the injectors to run rich when starting the engine cold. The IAC is supposed to provide more air thru the orifice in the IAC to give you a high idle. AS the engine warms up it backs off pretty quick. Do you have a high idle at cold start up? It should be around 1500 rpms. I don't really have COLD weather here, jeez, I don't even own a coat. But my Bronco will high idle for about 45 seconds, then start backing off. It takes it probably 3-5 minutes to completely stop the high idle. If you are not getting the high idle, the engine will be running very rich. You might look at the procedure on how to check the voltages of the IAC when cold. Considering it is a 95, you might be looking at an ECM dying. The only way I know to check one is with the nose. If it smells like it's burnt, it's dying. I had to replace the one in my Bronco a few years ago after chasing code after code after code. By the time I finally replaced it, I had all but rebuilt everything under the hood. That was okay because it became a complete rebuild project. Now I'm down to paint and interior which isn't too bad.
Another thing you might check. There should be a vacuum line that runs to the MAP. You might pull that line when cold. It should kill the engine or at least make it run extremely rich. That will basically opens all of the injectors to maximum fuel. There should also be a wired harness into the MAP. Make sure it's plugged in and that you have the correct voltages or it will run rich.

 

So tried a new ECM. No affect. It seems to be focused on cold starts or initial choke mode. Once it warms up you can clearly hear it clear up and run fine. If the truck is cold.. it takes longer. But once the engine is warm.. it runs fine. It isles high initially like it should. If you press the gas during that time it tries to die out and begins it’s struggling and back firing under the hood. I

 

Just for grins and giggles, I think I would clean the throttle body and put a couple bottles of Tehron or Gumout with PEA in the gas tank.

 

Well, so much for the simple stuff. So, don't assume that new parts are good. You need to check the fuel pressure. The ECM assumes 38lbs pressure regardless. It does NOT read the actual fuel pressure. If the pressure is higher than 38 lbs, it will run rich at cold start up. If it's over 40lbs, it's out of spec and needs to have the regulator replaced. I would also suggest running a bottle of Techron thru the gas. Put it in a half tank and drive it around at various speeds. Do this over several days to allow an over night soak. Next, pull the vacuum hose from the MAP, it should have the injectors go wide open and basically flood the engine. Next, pull the vacuum line off the manifold port that goes to the MAP sensor. If you have a vacuum pump, pump it to 5lbs vacuum. If not, suck on the line as hard as you can. It should make a difference in the idle. if the MAP won't hold vacuum, either the MAP is bad or the vacuum hose is bad. Next, pull the plug on the TPS. If it clears the rich idle, the TFI can be bad or the MAP is bad, assuming that you have inspected and tested all vacuum lines. If a vacuum line is bad, it will not run at cold startup correctly and will run rich. If they've never been replaced, do it now.

 

So update: took it to a master tech who has the ability to read OBD1. The system is showing it’s running rich, but the 02 sensor is reading lean. Already replaced the O2 twice to make sure... sensor reads the same. He’s talking about a back pressure test. I’m assuming he talking about a clogged up exhaust system? Could that be an issue?