P0300/P0302 and Flashing CEL
I've been getting the P0300/P0302 issue on my '05 I5 Chevy Colorado in the last few weeks. It was happening in conjunction with a really rough idle. One year ago I also had the rough idle but cleaned the throttle body and replaced the plugs and things evened back out.
In the last month or two, the rough idle returned with a vengeance and I began to get the P0300 and P0302 DTCs.
So far I have:
+ Cleaned the MAF Sensor
+ Removed and thoroughly cleaned the throttle body
+ Replaced #2 spark plug ("old" plug had no abnormal signs of wear)
+ Swapped #2 coil with #3 coil. Error code remained on P0302.
+ Seafoamed through the vacuum line at the throttle body (this caused an immediate reduction in rough idle)
After the Seafoam last week, things seemed better, but now I'm getting an intermittent Check Engine Light which is flashing and has me slightly panicking. When flashing, the truck is idling rough again. It only flashes on a cold start and after decelerating, and only every now and then. Not reliably.
My next planned steps are to replace the fuel filter and to do a Techron Fuel System Cleaner on my next empty tank. (Also an oil change).
But beyond all of that, I'm at a bit of a loss for what else I should be checking and trying for. I am aware of the P0300 service bulletin from several years ago, but I just started having this problem and these codes in the last few months, which is a little late for the service period in that bulletin.
Does anybody have any other suggestions for troubleshooting and repairing this issue? I would really prefer not to have to go get a leakdown test, if possible. I'd also like to avoid replacing the entire head since the truck is 12 years old and just doesn't need that level of investment any longer.
Thanks for your help everybody.