High Compression, p0300, rough idle, dark coolant!

[gsxcellent]

Ok so I have searched and searched through many many threads and have changed my mind about what is wrong multiple times.

My idle is horrible and i can hear it missing, The computer first threw a cylinder 4 misfire (p0304) then soon after threw a multiple/random misfire (p0300). i have changed the plugs and wires and i have tested my coil. Gapped my plugs to .028. All is good with spark. Cylinder 4 sparkplug is VERY black with carbon showing rich conditions. I did a compression check just for grins and giggles and here are the results:

Cyl 1-195
Cyl 2-180
Cyl 3-185
Cyl 4- 195

Very high possibly from carbon buildup?!

I also have a cracked manifold and my coolant is very very dark. (not sure if those two problems have anything to do with my rough idle tho)

Trying to make this post as short as possible, I was thinking maybe bad O2 sensor (80$), clogged injector, or leaking intake manifold (although i tested the mani with propane and did not discover anything)

Injector cleaner went in the tank today and thanks in advance to all your help!

 

[nightspeed87]

well i imagen that a cracked manifold could result in your idle...
Dark coolant? Maybe your head is cracked also? How did it get cracked in the 1stplace//
And yea those are some high compression ratios, most likely is carbon isnt the stock 2gs compression only in the 180s? (* Would be useful for me to know since im putting 2g pistons in my 1g 6bolt engine going in. )

This is one of those times were they say older engines perform a little better than when new.... ( maybe )

 

[gsxcellent]

OK, so i got enough energy to go in and remove my fuel rail and injectors, sure enough cylinder 4's injector had a destroyed o-ring seal on it and it looked a little burnt. I replaced the seal and switched it with cylinder 2 to see if the problem followed it.

The cracked manifold occured under normal conditions...not rare with the stock cast piece...and im sure your right about it having something to do with the idle as well.

More results are to come, please continue to post any ideas, THANKS!