I have a 1997 Tahoe and I have been getting a "Service Engine Soon" Code P0306 (Cylinder 6 Misfire). Before this code, I had a bad O2 Sensor code and I ran with a bad O2 sensor for quite some time which I don't know if that has anything to do with the misfire, but I figured I'd throw that out there. This misfire code prompted me to change the existing Bosch Plugs to AC Delco Plugs and I changed the bad O2 sensor. Note: When I changed the plugs, I unplugged the battery, which clears the codes. So I drove it for a while with no problems, and then the code comes back again (Cylinder 6 Misfire) with a noticeably rougher idle. I tested all the components of my ignition system with an Ohm-meter, and they all have the correct resistance.

Now, when I get this code, my truck runs noticeably rougher, as if there truly is something physically wrong with my ignition system. So I thought maybe if I unplug the battery and clear the codes, this rough idle will go away... and sure enough! every time it idles rough and I clear the codes by unplugging the battery, it's back to running just fine.

This leads me to believe that there is absolutely nothing wrong with the physical components of my ignition system, because if there were, shouldn't it misfire all the time regardless of the computer being cleared??
It's almost as if the ECM is encouraging the truck to misfire. If thats the case, can I just buy a new ECM to cure the problem? Anyone run into this before?

well on a 97 disconnecting the battery will not clear the codes. more like what youre doing is resetting the readiness monitors, fuel trims etc. something that doesnt run until a monitor has been run is a likely culprit. throwing an ecm at it is your call but i can tell you its probably not goign to fix the problem. if you cant figure it out its probably a good idea to have someone look at it that knows how to diagnose those kinds of things.

It could be one these causing the missfire,a bad plug wire,bad plug or fuel ingector.You do not want to buy the ECM,an Ac Delco program on a pentium 4 computer and a GM Tech 2 has to be used to program the new ECM.If it is the fuel injector,you have to buy the whole thing,about $400.00 and it looks like a spider under the upper intake

I just corrected a P0307 on my Tahoe. There was a slice in the plug boot of the no. 7 cylinder. Same symptoms you described. I put an extra plug in the no. 7 boot, started the engine and received a healthy shock when I tried to pick it up by the boot and move it near a ground to see if my spark was good-it was (ouch). I wrapped the boot with electric tape (it was arcing to the exhaust heat guard) and it worked fine.