i would definatly check the timing belt and gears and make sure it hasnt just jumped a tooth or 2, also remove the timing cover and check the gears at the crank and oil pump, they can wear and cause a slip.
When you check the timing rotate the engine around till #1 piston is on TDC, verify that with the mark on the crank pulley, it has a knotch that lines up with a mark on the timing cover or a mark or pin on the block.
Once you get the crank verified at TDC check the other timing marks on the gears, there are dots etched into each gear and a marker on the block or a pin they line up with, on the head where the head and block meet on the alternator side of the engine there is a marker in the cover assy and the dots on the cam gear should line up with that. Also verify that the rotor in the distributor is lined up at or near the #1 plug wire on the cap.
If all this lines up correctly then your problem is not timing.
If the rotor does not line up and is off from the #1 plug then the timing belt has slipped and you'll need to replace the belt and retime the engine (and oil pump gear, it is balanced and has to be timed as well).

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had to edit this, said water pump pulley by mistake, should say oil pump gear which i have corrected ;o)