Help my 1987!!

[Gregs71]

I did a lot of searches but didn't come up with anything real solid so I thought I'd ask. The truck is a 1987 3/4 ton 4x4 with TBI.

What I am describing only happens after the truck is warmed up. When I start to step on the accelerator the motor starts to sputter. When it sputters I get a loud popping / backfire noise coming from the engine compartment (I might say from the dr side, but the sound could be traveling from somewhere else). There is also a slight backfire from the tailpipe. If I let it idle or coast it seems to be ok. If I put it in neutral and rev it up, it seems to be ok, too.

Does that mean its lean? I am leaning towards the 'coolant temp sensor'?

I bought a conde reader, but I only got Code 12 which means everything passed?

Help me out guys, this engine popping scares me.

Thanks, Greg