Oldsmobile/Buick Repair: 87 chevy truck, air control valve, vacuum leak

Question
I have an 87 chevy truck with a fuel injected 350 engine. The engine idles up and down and runs rough when it is cold. After it warms up it runs perfect except when your siiting at a light it will sit there and run perfect and then the idle falls off after a minute or two. I have replaced the idle air control valve, the o2 sensor, and the fuel filter. nothing helped. could you please help me with my problem. thank you very much.

Answer
Hello Perry,
I would want to check the fuel pressure and make sure it is maintaining about 13 PSI, especially during those episodes.

And check for a vacuum leak, especially in the brake booster. You are sitting there holding the brakes applied. Try shifting to park and take your foot off the brake.

Van