1997 Honda Accord New Valvle Job

I just had a new valve job on my car, then about 3 weeks later the engine light came on and the car also started vibrating when you start it up, but it goes away as soon as you start accelerating. I took the car up to the dealer and they told me it was misfiring going on. They also told me the mechanic that did the valve job did a very poor job, so they did the valve job over, but they are not sure what is causing the vibration when you start it up. They told me they did all the checks and everything came back as being fine, but 3 days later (after bringing it back from the dealer) the engine light is back on and the car is still vibrating when you first start it up. The car sounds completly fine.
The reason my valvles went bad is because the mechanic did not change the tensioner when he replaced the timing belt, so 20 minutes after putting on the new belt, the bearings fell out the tensioner
causing the belt to jump, and therefore damaging the valvles