97 Ram with a 360. When you first crank it up it will miss and idle roughly. As soon as you give it gas it starts sputtering and won't pull and backfires. If you throw it in neutral and open it up wide open it seems to clear out and will miss forabout another minute and then will run perfectly until you park it again and let it cool down. The check engine light isn't on by the way.

A few things I think it may be:

1) Crankshaft censor (already changed didn't work)
2) Clogged CAT (should run bad when hot if this is the problem)
3) TPS - gonna try to pick one up this afternoon


Any other suggestions?

 

Pull the IAT off of the back of the throttle body and clean it. Also, leave it plugged in and have someone turn the key to the "ON" position. The plunger should move. If it doesn't, then replace the IAT.

 

You're probably over fueling at start-up. I would add these to your list:
map sensor
iat sensor
o2 sensor

The pcm doesn't use the o2 during open loop, but it does use it to write fuel maps during closed loop. It sounds like your plugs are getting wet. Could be an injector issue too.

 

I usually run Marvel Mystery every few tanks in both my Ram and my Cavalier to insure my injectors are lubricated and prevent an injector from sticking open. Good point about the potential injector problem.

 

Injectors are going to be hard to troubleshoot, especially if they are just a little sticky when they're cold.
A scanner will tell you a lot about what's going on, i.e. initial map and iat readings and where they go from there. Also will tell you o2 voltage and fuel trim.

Could be the tps, but the pcm relies more on the map for fueling. will adjust to the tps, but bad map readings duringopen loop will make the pcm think that the throttle is open when it's not or visa versa.

I bet if you reset the pcm, it will run fine for a period of time, then start acting up again.