I have posted this problem on multiple forums and group sites yet still have not seemed to get a clear answer. I have a 1989 W250 Pickup with a 360 cubic inch (5.9L) TBI V8. The truck has been in my family since 1992, day from 2005/6 until 2016, and only has 48k miles on it. In the past year, it has developed a problem where it would pop under acceleration. Seemed to come from the throttle body. Since then, the truck has had many sensors and other parts replaced pertaining to the fuel, spark, and air delivery aspects of the engine, with the only remaining original parts being the IAC and the O2 sensor (all other parts were original to the truck too before being replaced). Within the past few months it has gotten worse, where the truck would completely die under acceleration. Usually after this happened, it would start right up and act fine. It would also produce a rotten egg smell, which we (my father and I) was a result of the engine running rich and the catalytic converter. Since the end of November, it has gotten a new fuel pump, a new fuel pump module (the plastic thing that goes into the tank. The supply fitting snapped on the old one so I got another from a parts dealer), new EGR valve, and new injectors. The O2 sensor was also going to be replaced but it is currently stuck in the rusted manifold on the truck with no intention of leaving. It seemed that after the EGR valve was done, that it ran worse, with a noticeable fuel surge. Now I am an 18 year old college student with a seasonal part time job and slight mechanical knowledge, and my father has more knowledge than I do but has not dealt with Mopars or anything like this.! What could you possibly be causing the trouble? I ran the truck earlier today with the O2 sensor unplugged and it never tripped a code or a CEL. No codes or CEL has ever been on. I can provide links to the videos I’ve taken of it if necessary

 

Did it run any better with the O2 sensor unplugged?

Might want to remove the IAC, and clean the bore really well. (don't mess with the pintle though..... that'll screw it up.)

 

 

It's not a iac (idle air control) It's a ISC idle speed control(motor).
When you shut the truck off the ISC kicks up the idle for the next time it starts. If you watch it when you shut it off you will see it moves the throttle. When you replaced the fuel pump did you replace the fuel filter(external from the tank)? You might go over the ignition again and check for loose connections wires to close to each other bad cap/rotor or plugs. This sounds like what is causing the "pop" from the throttle body.

 

did you also replace the hall effect sensor in the distributor? also what brand o2 sensor did you use?

 

 

 

have you pulled the codes to see if the computer is seeing any issues? i would consider replacing the o2 sensor. make sure to use a ntk brand one. they are usually only $30 from rockauto. also i don't know if it is a good idea or not but you can possibly relocate the oxygen sensor to the y-pipe if you want. i really don't understand why they put it in the exhaust manifold for the early models. they even have an extension wire run accross the engine to plug the oxygen sensor into the manifold. it almost seems like they were originally going to stick them in the y-pipe but someone changed there mind after. i installed the oxygen senor on the y-pipe for my 89 and is seems to run just fine but anything would be better than running it with no oxygen sensor at all.

 

 

ok as long as it isn't a Bosch. their design for these trucks is completely different than stock and junk. i am pretty sure i got a denso in mine and it runs pretty good but it was free. if you are going to try removing the sensor make sure to do it while the engine is super hot. i think it will be nearly impossible to change it while the engine is cold. i thought i was going to snap the one in my 93 when i was removing it with a pipe wrench lol. this is also why i suggested possibly relocating it to the y-pipe if you can't get it out. installing it in the y-pipe would make it easier to get at if needed and should give the computer a better idea of what is going on instead of only getting a reading off the 1 side only.