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 Posted: Jun 24, 2019 10:40AM
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UPDATE: It was badly cracked/broke valve in cylinder 4. It looked similar to peeling back a finger nail of the finger bed (Bad visual, lol). Cylinder 2 had some burned valves. All and all, the head was tired (160,000 miles). So I obtained a remanufactured head and went to work rebuilding the top end of the motor. The car runs like new now. Thanks for all the help.

 Posted: Jun 18, 2019 03:42PM
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Thanks again for the input, I guess I am going to have to take the head off and figure this thing out. I hope to update soon.

 Posted: Jun 18, 2019 03:44AM
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CA
Probably burnt or sticking valves. Since you mentioned the problem was intermittent, I'd suspect sticking or fouled valves.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Jun 17, 2019 08:55PM
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So I have completed a compression test and results were: C1=172, C2=150, C3=175, C4=82.
Any idea what a drastic difference like that (C4=82) means?
If I have 160, 000 miles on this car, is that mid-life or time for a new one?

 Posted: Jun 15, 2019 06:00AM
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If it has individual coils verify power and ground, buy a noid light that plugs into the injector harness connector and see how it looks when misfiring compared to a good cylinder.

 Posted: Jun 15, 2019 02:54AM
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Sounds like your engine management. ECU

 Posted: Jun 14, 2019 05:49PM
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While I wait for the tools to perform a compression test, are there any other Ideas?

 Posted: Jun 13, 2019 08:17PM
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Also i should note that this intermittent and not 100% of the time. This is my daily driver and the yellow light has stayed on now for about 2 weeks while I have been trying all the other parts. I drive it to work (10 miles one way). It may usually only shows its ugly head when i come to a stop or after about 20 minutes of driving. Once the light even went off for about a day. then the symptoms returned.

 Posted: Jun 13, 2019 07:41PM
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Thanks I will check into that and post the results.

 Posted: Jun 13, 2019 07:27PM
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US
Have you checked compression in all 4 Cyls?

A burned / Cracked valve will have a missfire and bad idle.
WOrth a check. Been there done that .

 Posted: Jun 13, 2019 06:48PM
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Hello All, I have a 2002 base model Cooper with a standard transmission. I has persistent P0304 code (misfire in number 4 cylinder). The car will have a rough idle and the yellow "service engine soon" light will begin to flash. If I try to accelerate while the light is flashing it is a very noticeable vibration and misfire. 
I have replaced:

coil pack
spark plug wires,
spark plugs,
fuel injector,
fuel pump  
fuel filter,  
gas cap.

The symptoms persist, I need help any ideas?