Chev Express Van

2003 Chev Express Van Engine Dimming When idling Always

My vehicle is miss firing. I also miss fires at very low speed. My mechanic thought it was the map sensor but its not he got a decoder for it and it says the problem code is P003. He changed the spark plugs, and clean the injectors. How can he fix that problem?

Are you sure this is a 5.7L and not a 5.3L?
Do you happen to know which troublcode set first?

Follow the information on the plug wires, coils, and then injector terminals.

The code should be longer. Ex- P0303, P0400, etc. If you can't remember the exact number visit Autozone or Advance Auto (there may be other stores) and have them scan for troublecodes. They do this free of charge.
Write down the exact code(s), pay less attention to their definition than the actual number.

I have just gotten the correct information. Its P0300, random multiple cylinder misfire detected, and P0172, system too rich, bank 1.

Thank You

Which engine do you have?
How is idle, is idle rough with erractic idle speeds?
How is performance on acceleration and at highway speeds?

Spark plug wires and coils are a common cause. Inspect and replace as necessary.

Injector terminal corrosion is another place to look. Apply a small amount of electric grease to injector connector terminal. Then plug and unplug the connector several times.

I have a 5.7L Gas Engine. It dims on idle, at times when accelerating it stalls a bit and at high speed the RMP fluctuates.