what is the factory setting for a 1997 silverado 5.7 on the timing when hooked up tu obd goes from 16 to 28?

Question

trouble codes are maf sensor and cam shaft sensor car starts and runs fine then sometimes it wont start

it goes that far at a idle

Answer 1

If you are indicating the "sync" signal, is it positive or negative?
If it is showing "-16", it is negative.
The sync wants to be "0" plus or minus 2 degrees, and should remain there all the way up to 3000 RPM.
If it is late (negative), chances are that either someone tried to adjust the timing with a timing light, or the distributor gear has eroded, and is due to fail all-together. The only way to tell is to remove the distributor and inspect the teeth on the gear.
If the teeth are still square on the top, then reinstall the distributor, and adjust the ignition timing with the scanner, and bring "SYNC" into range, and check it through the entire RPM range.
If the "SYNC" signal is advanced (+16), the distributor has been moved for some reason, either an uneducated timing adjustment, or mal-adjusted during engine repair. (Int. Manifold Gaskets?)

If you are refering to the Timing Advance on the scanner, this is the advance above BASE timing that the PCM has advanced the ignition timing. It is used for troubleshooting and not for adjustment.

Good Luck