2003 Chevy Silverado Chevy 5.3 multiple misfire

Engine Performance problem
2003 Chevy Silverado V8 Two Wheel Drive Automatic 109k miles

I have a 03 5.3 ext cab LS with 109k. Today I was on the highway had to punch it to get around traffic, at high rpm I lost power and the engine light started flashing. Later that day I was driving and got on it again same thing happened. Then on my way back it just started missing out like crazy on normal throttle and the engine light was flashing again, at stop lights it was trying to die. I went to a parts store and ran codes, got MAS code and random misfiring code. So in the parking lot I replaced the $80 MAS. Didn't change a thing, cleared the codes and let it run till the light came back on. This time it was only random misfiring code.

So I limp it home, then check plugs and wires. They were original and had planned on changing them any way, but now only had plug money. New plugs ddn't help.

Well I continued to investigate, Noticed a noise that kinda sounded like a diesal engine from the center of the engine, used to only make this noise when it was cold. I sprayed carb cleaner all over the intake looking for leaks. No luck there. Please help! Need my truck for work.

PS I recently replaced the door speakers, not a bose system so I don't think ths maters but I don't know. Anyway yesterday got in my truck and the radio wasn't working. Could change stations but no other buttons worked and no volume. Later it was back and working fine, but the clock reset. No probs since.
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Friday, March 20th, 2009 AT 12:41 AM

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2003 Chevy Silverado Chevy 5.3 multiple misfire

Could be caused by the following:

Faulty spark plugs or wires
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector(s)
Burned exhaust valve
Faulty catalytic converter(s)
Stuck/blocked EGR valve / passages
Faulty camshaft position sensor
Defective computer
Possible SolutionsIf there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.

If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.E. Spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.K.A. Coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open
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Friday, March 20th, 2009 AT 1:14 AM

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