My car was running excellent prior to taking it.

My car was running excellent prior to taking it to my mechanic. I brought to my mechanic for a standard mantenance. When they told me that my car was ready and I started it, the car puttered and barely would move. This was a starked difference than how it was running when I brought to the mechanic. The mechanic checked the engine and used the computer to diagnose to find the problem. He replaced the gasket for the distributor because he said he saw some oil leaks. Also he checked the spark plugs and wiring. Other checks included fuse box, filter and battery. Another mechanic came to assist and he said it was possibly a lack oxygen and adjusted a screw that increases air flow. None of these seemed to solve the problem. The first mechanic said that it is an electric problem. What could be some solutions to the engine running without puttering and dying out?