My 95 acted in a very similar manner. After about several trips to the dealer and about a $1000 on parts and repairs that they thought were the problem. The only thing left to fix was the pcm. Replaced it for $400 and now it runs perfect (except for the plenum leak).

 

Thats what im trying to avoid. Just throwing parts at it. I know if i take it to the dealer or any shop really they are just going to throw parts at it. When i get a customers car in i try and find out what the problem is and not just replace parts that dont need to be replaced.

My father seems to think its the PCM, but thats a big price tag when youre not sure.

 

I can't get away from the sucking sound you mentioned. Have you checked the TB shaft for excessive wear or the TB gasket? I know if a carb has a lot of slop in the throttle shaft, you will never be able to set the idle.

 

The sucking sound is the Idle air control valve pulling way out at idle. It should be in almost all the way at idle but for some reason when it starts running bad it starts to adjust outward, causing the loud sucking.

 

If possible, check the fuel pressure while it is running bad. You should have 35-45 psi.These fuel pumps can malfunction in strange ways before going out completely.I had a similar problem with mine and it was the fuel pump.

 

+1

Many a time I taped a fuel pressure test gauge to the windshield and went for a road test.

Don't forget the basics you need spark and fuel to make it run.

My money says its a fuel supply issue. It should be 49psi +/- 5 psi while running.

 

Im not seeing where to hook up a gauge on the fuel rail. I see that one spot where the fuel comes in but that is the only tap in. Unless you have a special "T" i dont see how i could check fuel pressure while the truck is running. Could someone help me out with this, i did several searches.

Spark and timing are fine, my solus shows the timing adjustments. When it runs like crap and shuts off i can start it right back up and it still runs like crap.

I did take of the TB today and checked for the plenum leak, I didnt see any major amount of oil on the bottom of the valley cover. Just a thin layer, could be a small leak. I did the vacuum check and didnt notice much of a vacuum.

I changed the oil in the truck today and fixed the cruise control vacuum line. I thought about the fuel adaptives and from what i read, the front O2 is responsible for making adjustments for fuel. So i unplugged it. I let the truck run while i did maintenance on other cars. It ran for a good half hour, just idling, no problems at all, didnt even throw an engine light. I drove it up and down the road, and down some back roads, came to several stop signs. Never a hint of running bad. I came back to the house and let it sit, still running. Went inside and washed up for dinner, came back out to shut it off and the engine light had just come on, but the truck still ran fine.

Thats about a good hour non stop of running and it never acted up. Since my father brought it to me it will start acting up the first mile or so you drive it. But when i unplugged the front O2 it didnt act up at all. Opinions?

 

If it happens in the first mile or so it is NOT the O2 sensor. O2 sensors are only monitored by the PCM in closed loop operation after the engine reaches operating temp.

My money is on the fuel pump. Specifically, there is probably a clog in the pump and when you idle, you're dribbling gas into the engine. The moment you step on it, you're pushing the pump and the clog restricts it.

There should be a schrader valve (same type of valve as on you tires for air, but a different size,) on the fuel rail somewhere, covered with a screw on cap. I have never seen a truck without one, but I have heard that a few model years did not have them.
The only other things I can think of that might cause you problem (other than the PCM) is a faulty EGR valve or clogged catalytic converter. A clogged cat typically throws random misfire codes and makes the engine feel like its pulling way more weight than it should.

 

Some trucks don't have the fuel test port (schrader valve). Stupid Dodge!
My 97 doesn't have one, I had to make an adapter hose with a 'T' in it to test fuel pressure. Dodge dealers have the same factory adapter hose.

I would try to test fuel pressure first but unplugging the front O2 is diagnostic.
By unplugging it you keep the truck operating in open loop and the PCM will input it's own default value for the O2.

I would try driving for a few days with the front O2 disconnected and see if it acts up.

If it behaves then replace the front O2 sensor. If the sensor has been on the truck for more than 80K replace it anyway.

O2 sensors lose their sensitivity with use and can give false readings. If it is giving a false rich reading your PCM will lean out and starve the engine (much like a bad fuel pump) the IAC opens way up to allow more air to try and keep the engine running if the RPM is below spec (due to the fuel starvation).

Can you do an O2 heater test with your Solus? A bad O2 heater can also make your truck idle like crap but generally smoothes out while your driving (due to the increased exhaust heat from driving)

Good luck!

 

Exactly. The PCM runs on sort of a default, but the truck runs fine. Which leads me to believe that the fuel pump is fine, if the fuel pump were going bad the truck would act up in either the "default mode" or when in "regular mode". But i wont rule it out until i can check the pressure. Yes i can do a O2 heater test with my solus, ill have to bring it home tuesday.

And yes i must be one of the unlucky ones without a test port. I know what a fuel line test port looks like, ive tested many other cars, but this one DOESN'T have it.