I just bought this nicely used 1991 GMC Sierra 1500 series pickup truck for $650. It started up and ran fine when I gave the seller the money - the few leaks in the break lines.
Easy fix right!
So my son (19 that knows it all) and I went and changed all the break lines (made everything one size 3/8 line.) Filled it up with break fluid and started the truck. I had my so pumping the breaks and holding them (his first time) I bled the far rear (passenger side) then I had him turn the steering wheel to the right so I could bleed the front driver side.
He turned, and turned and turned until the the engine died. 
Now the truck only runs when the steering wheel is turned all the way to the right or all the way to the left.
Going to pull the codes to see what the heck is going on…
Any help other than that is very appreciated!
I can’t explain exactly why it is all the way right or left, but it seems likely that you are having a problem with the power steering pressure switch. It sends signals to the PCM about PS fluid pressure so the PCM can adjust idle to handle the extra power needed by the PS pump
Where is the power steering pressure switch located on this vehicle?
The codes it pulled up was 12, 15, 34, 45
Ok. Have you tried to make the truck run by giving it some throttle? There’s a good possibility it is running too rich (#45) from a bad coolant temp sensor (#15). When you turn the wheel all the way one way or another the PCM kicks up the idle so that may be compensating enough for the rich condition. I would check the coolant temp sensor - its just a resistor and can be checked with an ohmmeter, though you also need to check its wiring. I don’t know the resistance specs but you might be able to get them from Autozone’s free online repair info if you don’t have a manual.
I can’t tell you how the MAP sensor code (#34) fits, but hey - this is all basically guesswork with little info anyway. The #12 code is just saying the error code system is ready / passed whatever self-check it does. It’s always the first code.
I can’t help with the car but brake is what stops the car. Break something is what you did when fixing the brakes.
I used electrical cleaner I got from Autozone and took every connection apart and cleaned real good.
I got it home and did changed spark plugs (they look like original ones) and wires…
I found a few dry rotted hoses so I replaced them all.
I gave her a “over needed oil change”, (no medal found in oil) and while down there I also took off all the plugs and cleaned them as well.
New air cleaner and found on bottom of air cleaner hose (looks like it melted just a little holes" so ducked tape them until I go to a “YouPullIt”
Last thing I flushed out coolant and gave her a fresh drink.
Time to rest the PCM and she how she dos now.
I thank you for all your help and the laughs.
Well it just shows you a little TLC and talking nice to your vehicle goes along way! Took a test drive for about 25 miles, she ran like a dream 
Last thing I did is get the wiper motor to work. It kept blowing fuses. So I raped a fuse with al foil and had son tap on wiper motor while I turned it on and walla It works like new again.
Again thanks for everyone’s help!
Yeah but now during a rain storm you will have a fire under the dash in the fuse box from the aluminum foil wrapped fuse when it overheats since you have a short somewhere to your wiper motor
Old post. But I’m curious how you could rape anything with aluminum foil. And if you do, is it illegal?
Lol yea your right it did catch fire a few times. Must of been from all the rapping going on…