I have a 1991 d150 with the 318. This winter is the first time its had this problem. I go out to start it and it fires right up like normal but seems to run a tiny bit rougher than normal...like is not firing on all cylinders. If i put it in gear and try to move it right then it will die. If i wait for 10 minutes or so until the motor warms up enough then it behaves normally and doesn't want to stall out on me. Im assuming its some sensor gone bad but I'm not sure exactly which one. I checked the resistance of the coolant temp sensor when it was warm and when it was cold and the readings were changing so i assume its fine. Thanks for any help.

 

 

Thanks i will try that this weekend.

 

Ok so i pulled the codes. If i did everything right i got codes

12
33
37

The only troubling thing is that code 33 seemed to flash a few times before i got to code 37. I looked up what those codes are and non seem like they would cause my running issues. 12 i can ignore as normal...33 was something to do wit the AC circuit (my truck does not have AC) and 37 was the neutral safety switch or park solenoid i think. Am i missing something here?

 

37 is baro read solenoid open or shorted. I will look this up at my shop Monday and get back with you. as you said 33 was a/c solenoid. newtjr

 

Sorry for the delay getting back to you. Looked up code 37 at my shop (Alldata) on your 91 and applies to torque converter unlock circuit. Pretty sure this does not apply to your issue. From the sound of your problem I had the same thing. Part of the cause was a restricted vacuum supply to the MAP sensor (located on the passenger side of the throttle body) which I solved by capping the vacuum at the TB and routing a vacuum line to the fitting on the brake booster. However, I wound up replacing the MAP sensor. If you have a good repore with a parts supplier such as NAPA Autozone etc they may let you return the part if it doesn't work. newtjr

 

Hey thanks for getting back to me. I will see what i can figure out and hopefully update this thread soon.