You got to muzzle it j/k

p0303 is physical cylinder number three, facing the engine back bank rightmost cylinder.
How many miles? What maintenance done?
Typical suspects are plug/coil/fuel injector/valve out of adjustment.
These old ones also had issues with EGR carbon build up

 

Just checking because I saw where it meant the 3rd cylinder in the firing order. so, that 's why i asked.
Thanks,
Buffalo

 

had the egr intake port carbon up a couple times on my old 2001.
take the intake off use a drill bit to clean the port. worked like a charm.
couple DIY videos on youtube about it.

 

I only get that 1399 code when the ambient temp is around 32F or colder.
Same with you?
Thanks,
Buffalo4

 

My '03 started running rough and displayed the flashing engine light and then the TCS lamp came on. Codes read: P301, P303, P304 and P1399. All posts seem to point to coil pack or EGR. I've had several coil packs replaced and do not recall the TCS lamp lighting-up previously. Any words of wisdom?

 

The TCS light can come on for MANY different reasons, including misfires. Take care of the misfire problem first, which could just be a bad coil pack or a loose spark plug (many times Cyl # 5 , front center) which can burn out the coil.
Do the 'coil drop' test to try to figure out if a particular coil is bad. Hopefully that is all it is.
If it is also shifting rough or strange, more investigating is warranted. All you codes have to do mainly with ignition type problems or possibly a valve lash adj problem or even an EGR problem.

When they replaced some coil packs previously, did they use Denso or OEM coil packs?
Buffalo4

 

The TCS light can come on for MANY different reasons, including misfires.

Yep, it means only that your TCS has been disabled by the computer due to a powertrain fault.

Follow the codes to find the problem