Valve tapping?

Well after rebuilding the head and sorting through several problems, I'm nearing the end. The car will start but it sounds as if there is a valve tapping, it's not very loud though. I think the ignition timing is off since the distributor and coil were taken apart. How do I go about adjusting the ignition timing? Do I have to set this manually through the ECM?

I forgot to add I also ran the computer on the car, there are no misfires or anything like that, the only thing that comes up is p0122. Which means theres low voltage to switch A of the throttle position sensor (TPS). I'll just get a new sensor, but this wouldnt cause the tapping.

well I reset the ignition timing...and apparently things only got worse. The car still taps, so it was not the timing I guess. But now I also have multiple cylinder misfire says the computer...but I kinda thought I had it before also. All the spark plugs are gapped correctly to .060 inches, and all the plug wires are wired correctly. What could be the problem?

What engine? It may not be ignition related at all.

3.1L engine, thanks

I purchased new spark plugs, this time AC Delco instead of Bosch and the car does sound better. I replaced the coils, I put Marvel mystery oil in the car and now it taps still, but a little less. I replaced the TPS since the sensor was bad and now that code stopped going off, but now I have a continuous random cylinder misfire. The service engine soon blinks instead of staying on during idle, but stays on permanently when accelerated. Could the cause of this be another sensor? Idle air control, knock sensor, or cam sensor? Would these codes show up on the computer also? All the computer shows is p0300 cylinder misfire.

EDIT: I also forgot to add that when i switch into another gear the engine usually drops in rpms and tries to turn itself off until the gas is held steady.