I have a 2001 Chevy Silverado 4.3 V-6. No check engine light and misfires like out of time or bad gas. Pops out the exhaust. Shows codes P0300, P0430 and code for map air flow sensor. i have checked all the above and i cleaned my throttle body completely and still have the same results . checked all plugs and wires, did complete compression check and did a fuel pressure check . runs ok at an idle and while in park or neutal, as soon as i put it into drive and the engine is under load it runs really rough. i am stumpped and dont have any ideas . thought maybe bad gas or water in fuel somehow but added plenty more fuel and heat treatment. plz someone help me .

 

OBD2 - OBDII Code P0430 CHEVROLET - Catalyst System Low Efficiency Bank 2 | Engine-Codes.com

OBD2 - OBDII Code P0300 CHEVROLET - Cylinder Misfire Detected Random Cylinders | Engine-Codes.com


Did you check your o2 sensor? That's what one of the codes was suggesting for. It also would suggest changing the cat.

 

Might want to check fuel injectors. Might be dirty. I've been chasing PO 300 for over A yrs. If your cat is bad. Run A can of Sea foam threw brake booster hose.Turn it off for 5 mins. Then start it back up. Should help it out a lot. Hope you can fix yours. Next is the Cam sensor on mine.

 

i'd be checking for a clogged converter