Alright i might have trouble explaining this, so bare with me. I dont know if im posting this in the right place. So to start off i own '87 blazer 350 5.7 engine. So Ive had the truck about the 2 years. The truck always had a kick when changing gears from the tranny and leaks a little oil besides that the truck always ran fine. Let me know if i let some info out but ive read and try to pinpoint the problem.

...so the truck just recently started having this issue with engine. At first it seemed the truck wasnt getting enough gas when i start it and was idling the engine was reving on its own. Also the exhaust was breathing weird. so i took off the fuel filter and it seemed to be fine. Then i went on cleaning the carburetor with some carb cleaner and it sort of made it better. But still something seemed wrong. Ive took it to 2 small time mechanics and they couldnt really figure out what was the problem. They just told me i had code 15 & 44???..... so they just told me to replace the spark plugs, dis. cap, wires, and all that simple stuff. So i had change the plugs a couple months ago so didnt think i had to change those. I DID replace the cap and rotor. I also changed the oxygen sensor. And to add to it'll shut off when going in reverse.

So any help you guys can give me, i would appreciate thank you.

 

Code 15 is for the coolant temperature sensor which can cause all sorts of problems from over fueling to timing problems.

Code 44 is for the O2 sensor reading low voltage when in closed loop operation which indicates a lean condition.

It wouldn't hurt to double check that the distributor cap is sitting flat on the distributor base and that the wires are all connected properly.

After that, I would concentrate on the coolant temperature sensor by measuring the resistance when the engine is cold and you know what the outside temperature is, comparing the resistance with the values on the attached chart below. You can then warm up the truck if it will run that long and repeat. It helps to have an infrared thermometer to measure the temperature at the thermostat housing for direct comparison.

Hopefully the condition hasn't gone on for too long and caused the catalytic converter to become clogged. From your description of the exhaust, that may be the case.