2000 Silverado, 4.3L, auto
Intermittent check engine light illumination. When the light is illuminated, the engine runs very rough & is sluggish. Recently replaced the spark plugs with OEM, also replaced wires, cam position sensor, air & fuel filters. Fuel mileage has never been good but when this problem started gas mileage has become very bad. 8-10 miles a gallon. Light will not stay on long enough to get it to a repair facility.
HELP

 

About the malfunction indicator, an emissions event will stay in the control module memory as one or more historical DTC(s). They should be able to read it out and go from there.

 

When I had those symptoms, I replaced the distributor cap and it fixed it.

I have a '97 5.7, so I'm not sure if your (newer) 4.3 has a mechanical distributor or not. Please disregard this if not.

 

the 4.3 should have a distributor on it. if possible buy a scanner and have it with you while driving. when it comes on, park somewhere and pull the code.

 

New distributor cap was installed along with plugs & wires.
The code is 303 I think. "multiple intermittent cylinder misfires" is the code that is displayed. I have been told that Platnium plugs sometimes cause this code. I'm changing the plugs to standard or copper to see if that will correct the problem. Any & all ideas/comments appreciated.

 

When i've seen service light,the 02 sensors were old and I changed and i've had good luck with bosch platinum plugs.

 

Changed the plugs yesterday (again). Ran good for about 10 miles, then started missing again. No light yet. Plugs that were removed were fouled badly. They had about 6,000 miles on them.

 

Thanks to all of you that responded to my problem.
FOR THE RECORD...PROBLEM SOLVED.
replaced the gear assembly on the distributor which was badly worn allowing timing to vary by as much as 10-12 degrees. Chevrolet dealer in Columbia, TN
was able to determine the problem thanks to the shop mgr. (30 years with GM)
He diagnosed the problem almost immediately. Very impressive

 

Glad to hear. Thanks for the update. I'll be sure to file that information away.

 

My '05 4.3 is throwing the same code. I to have replaced plugs, wires, cap, & rotor. Truck runs good but if I try to push it to redline in 3rd gear it breaks up after 4000rpm, engine light flashes, and motor stops pulling. When I upshift light goes out and motor cruises along fine. I was thinking maybe coil, but now will check distributor. Thanks for the post.