Timing still off after Belt replacement

My Mechanic works at a GM Garage, he used to work at a Garage that worked on foreign cars, I had him change the timing belt on my son's 96 eclipse nt 2.0 with the 420A Engine, he didn't get the marks on the cam gears aligned right the first time, I ended up with a rough idle, but the car ran fine, I took it back to him again, he swears he had the cam gears lined up correctly the 2nd time, but guess what, I still had a rough idle, we took off the inspection plate has someone bump the starter until I saw the timing marks for myself, they are still off,we checked this 3 or 4 times, he is ready to work on it for the 3rd time, I have a new tensioner for him to install this time, he said maybe he would run the engine with the cover off for a minute or so to make sure everything lines up before putting it all back together, I don't know if this is a good Idea, because I don't want anything to fall into the belt and screw up the engine, any suggestions would be appreciated.

Thanks Mister D

its fine... you technically dont need the timing belt cover on... i see it as just to keep things out, i havent had mine on for about 2 years now and nothing has happend yet... also let him know... when doing the timing belt the crank shaft sprocket should not be directly lined up with the timing mark, it sould be half a tooth BTDC... the arrow on the block should be pointed to the groove right next to/befor the mark on the sprocket... everything else should be lined up... the 420a motor is not a easy motor to do a timing belt job on!!! personally i think it sucks! but just let him know before something happens to the motor!

Thanks for the information, I will let him know.

Mister D

3rd times the charm, I worked with him and with several attempts we were able to get it right, started the engine with the cover off to test it, only ran it a few minutes that way, now the Idle is good again and it runs great, The way we understood it is, you start with the crankshaft timing mark 1/2 tooth before TDC, then after routing the belt around and keeping the cam gears in the right position, you end up with all 3 timing marks aligned, the 1/2 tooth before TDC is just to help get everything aligned.