If the SES light is on, the technician will find a P0300-P0308 DTC with misfires counting on a single cylinder that may or may not be felt. This may occur consistently, or it may occur intermittently. If a tick noise is verified, it will not be eliminated by canceling fuel injectors and the noise will sound like a valve train tick.
It may be the result of any of the following:
1. worn camshaft lobe and/or lifter roller
2. a sticking valve
3. valve leakage
4. a broken valve spring
5. a collapsed AFM (Active Fuel Management) lifter.
Here's the full write up with a description of driving under certain conditions to test and diagnose the misfires
http://www.g8board.com/forums/showthread.php?t=25948
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