I have 1988 gmc sierra 1500 2wd 305 it run rough at idle speed in drive and dies out in reverse all the time I cleaned the iac valve advanced the the distributer a little that help in run smoother and seemed to slow down idle speed but the constant dieing in reverse and rough idle in drive has me stumped

 

It's most likely due for a tuneup. My Firebird with a TBI 305 did the same thing for the longest time until I replaced my burned sparkplug wires. It probably has a slight missfire that gets worse under load at low idle. Is your 88 carbureted or TBI injected?

 

yes it has a tbi and the plugs wires are old, the plugs are new and I put a new borg warner distributor cap with brass tops on it. actually only six plugs are new but I am on a limited income Thank you very much are probably right

 

yes is also has a tbi

 

Is it misfiring slightly? I mean it can be other things too. Maybe your EGR is slightly stuck open causing a lower idle than normal and it dies that way. IDoes your check engine light come on?

 

it flashes a few times then goes off I think. I will take it o'reilys and let them do a code check

 

With a truck that old, they'll send you away before you can even tell them what's going on. Their code scanners don't work.

Jumper the A and B connector on your ALDL connector and it will flash your check engine codes for you. See this link for instructions: How to read older GM OBD diagnostic codes for free

Code 12 is normal, I'm interested in the other codes

 

If it idles rough and dies when you put it into gear, I'd suspect a vacuum leak. That era had a real problem with the intake manifold gaskets, which don't cost much but takes a bit of effort to replace. Also, the fiber block between the throttle body and the intake manifold tends to harden and leak. If you have some Permatex 2a or 2b, use that, but don't use any silicone based sealer...replace the fiber block...under $10

 

Thank you, I want thank everyone here at truck forum for all the useful help, you all were very nice to me so thanks to everyone who responded to my post

 

Were you able to figure out what's going on with your truck?