Miss fire only when ho.when cold runs fine.code po303.

[chuck ray]

When its cold runs fine when hot miss fires

 

[nesralyrrej]

Po303 is a cylinder 3 misfire check your wires and plugs, check the gap and for any fouling. How severe of a misfire? It coul be a bad coil pack maybe

 

[chuck ray]

When the engine is cold runs very good.whe it runs for about ten minutes theN it codes po303 and misses.pulled number 3 exhaust plu gap was 70.instead of 44.pulled number 1 intake and was the same 70.have 137k on the plugs.

 

[nesralyrrej]

pull of your icm and take it to an auto parts store to get it tested. 3 5.5mm bolts hold it in place (i believe)

 

[paramud]

I had that and it ended up being low compression. 2 and 3rd cylinder. Headgasket between them was in bad shape, but mine had low power, low mpg, and rough idle.

 

[tomw]

Well, maybe you should do some normal maintenance. Spark plugs are wear items and need replacement or at least re-gapping now and again. A temporary check would be to re-gap the plugs back to the spec, and observe. If it now works, I'd replace the plugs.
The computer adds a bit more fuel when the engine is cold, so when it warms up, it will be given a little bit less fuel. The leaner mix is harder to fire than the richer one, so a iffy spark plug could cause more misfires when it gets a leaner mix.
If it runs well and has a good idle before the engine gets warm then the valves and rings are likely OK. You could do a leakdown or compression test to verify condition.
tom