1994 intermitently runing rough

[mwnmwn]

I know this is a long shot but the internet has held surprises in the past.

 

 

I have a 94, 305 two barrel throttle body, auto trans, 4X4 with 100K. From cold, starts and runs fine. After it warms up and waiting for a light to change it will idle/run rough sometimes. Sometimes it can be "cleared" up by raising revs in neutral. Sometimes accelerating from stop in this condition it will "buck" possibly backfire before it returns to normal. Worst case has been after being warmed up and going through one of these episodes, parked truck while running fine and 15 minutes latter it would not start. It fired and "tried" to start but would not. Let it sit for 3 hours, started and ran fine all the way home and restarted fine after a 5 minute wait once home.

 

 

I am assuming it is not mechanical or plugs as latter are fairly new and when running fine it will pull smoothly and strong past 4000 RPM.

 

 

Guess would be some sensor but which one, or hopefully not ECU.

 

 

Any help / suggestions would be greatly appreciated.

 

 

 

 

 

 

 

 

[TheRedBaron]

I had similar problems with my truck, I replace the coolant temp. sensor and it cleared everything up. Is there a check engine light?

[oldscsc]

+1. Let the truck sit overnight. Hook up a scantool and observe the ECT sensor reading. Should be within 5 degrees of the IAT sensor reading.

 

Alternatively, you can remove the sensor and place it in water. Use a thermometer to determine the temperature of the water. Then use an ohm meter to compare resistance at x degrees to spec.

[mwnmwn]

Thank you for the replies, gives me a place to start.

 

So far no check engine lights. At start up the check engine light does light so it is not burnt out.

 

Did either of you get a CEL when you had the problem?

 

I am wondering if you both had the intermitant and variable level of roughness that I have? Most of the time the problem shows up idleing in gear, sometimes the tac just bounces and not a smooth idle, several times once engine was "cleaned" out by raising revs the problem has gone away for the rest of the trip. The worst has been almost stalling several times getting across an intersection and again at the next light followed with not staring after a 15 minute shopping stop.

 

Again thank you very much for the responses, your help is greatly appreciated.

[TheRedBaron]

i got one, code 15.

that's exactly were i had problems, it was acting like a carburetor with the choke always on.