Ok first of this will probally be a long post.

I have been banging my head trying to figure out a problem. since i got this truck a few days ago.

I have a 98 ram 1500 SLT Laramie 4x4 with 318.

After about 30 seconds after start up the idle goes up and down between 400 and 800.

I can rev it to the moon if i want and it is smooth when cold.

It drives good for the first couple minutes also when it was cold. Once it gets warm it starts to pop and kinda like back fire thru the exhaust and i have very little power.......i can put my foot down and it will downshift then take off but still a little rough. Once i let of it is back to popping and back fire. Even at this point i can put it in neutral and rev it just fine ( maybe small popping as it comes back down in rpm's )

Okay now what i have done all ready.

New plugs (stock champion)
New wires (autolite)
New cap and rotor
I routed the wires per the tsb
I cleaned the IAC
Check that the TPS is working correct.
Removed the TB and cleaned totally. New gasket.
New upstream 02 sensor
Cat converter was gutted allready.
I found 1 broken vacuum line and fixed that. I haven't gone thru all the vacuums yet to look for leaks.

What am i missing? Would the plenum problem cause this?

PLEASE HELP ME BEFORE I SHOOT THIS THING AND FIND ANOTHER CHEVY TRUCK.

 

What brand O2 sensor did you get? It sounds for all the world like you got a bad one.... try unplugging it, see if that makes the problem go away. (will set a check engine lite.) Also, verify fuel pressure. Should be right around 49 pounds.

 

I believe they gave me a bosch one.....I didn't think about fuel pressure.

 

would this be good enough to test the fuel pressure?

http://www.harborfreight.com/fuel-in...ter-92699.html

 

That'll work great. Inexpensive too......

Bosch O2 sensors suck, and our trucks don't like 'em. NTK or Denso are the brands that are preferred.

 

Is it possible something killed it right away? Is there a way to see if power is going to or from a o2 sensor? I had to splice in wire to the one i bought because the lead was no where close to long enough.

 

erm, which one did you replace? You should have two... one right in front of the cat, and one shortly behind it......

 

I believe there is only 2 wires, so unless you crossed them in the splice. However, bosche historically do not work well as mentioned earlier. Just don't try to salvage it.

NTK or DENSO brands can be got online at Rock Auto. I never looked at local parts stores though (e.g., autozone, oreillys, napa, etc.).

 

I replaced the one before the cat. well it is sorta in the cat. the one after the cat i understand doesn't really do a whole lot beside show the cat is working and the cat is empty as of now.

 

The O2 sensor has four wires usually... two for the heater (same color) and two that go to the PCM (different colors).

+5000 for NTK or Denso. Bosch and Standard brands tend to be unreliable at best.