1996 Lexus ES300 ES 300 1MZ-FE is loud why?

Mar 1, 2008
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I have check engine light codes P0300 P0301 P0303 P0305 P0115 P0135 (o2 sensor, coolant temp, and misfire cylinders 1 3 5). However, the car is very LOUD when in drive and foot is on the pedal. However, it is not as loud when I'm moving and foot isn't on the gas or if I rev the engine while in park or neutral. It is worst when I'm accelerating from a stop but less loud if I'm already moving. There is no exhaust-related CEL code, nothing about the cat, or anything like that.

At idle, the sound is kind of reminiscent of the burbling Chevy small block. Accelerating from idle about 2000 rpm (racket starts between 1500-2000 rpm then gets just raucous after that), the sound is kind of like a loud slurping sound and marbles.

I have the CarMD, and they said either new spark plugs or new fuel injectors. I just got new spark plugs, and gas mileage is much improved. I put in a quart of Lucas fuel injector cleaner. The noise was the same before and after the new plugs.

Other than the loud noise, there are no drivability problems, no loss of power, no stalling, no sputtering, no engine knock, nothing like that at all.

What could it be?
 
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