Misfire Cold Start 02 V6 Sonata

First a little background which may or may not be of importance. Car recently has had a Mass Air Flow sensor installed for a bog/stall on acceleration. MAF was reading approx. twice the specified voltage at most RPMs. New MAF was installed and car left happy. As a matter of maintnence spark plugs and timing belt were installed. Car ran great for a few weeks until one morning vehicle was backed out of driveway and stalled. Vehicle would not start and was towed back to shop. Upon arrival it promtly started and was driven into shop. Check engine light has been illuminated several times for cylinder misfires. Usually a different cylinder each time. If the vehicle is allowed to warm up and shutoff the car will start fine with no servicable issues. New plugs and wires were installed to elimate at least one variable. Injectors were visually checked to verify that gas leakage was not fowling cylinders on long periods of engine downtime. Any ideas at this point would be worth there weight in gold. Thanks in advance. Ryan