Need some repair advice. Story a bit long...

Local repair shop replaced my timing chain, rails, etc, as normal maintenance, but didn't do it right (chain didn't break, but slipped or something), resulting in 3 bent valves.

They agreed to do the repairs under warranty, but had problems getting it (engine) back together (broke head bolt by over torque, other miss-cues etc, requiring more waiting. They had the car over 3 weeks.

After many delays and poor customer service (never calling me and repeated promises to have the car ready were unkept), they finally got it running.

I picked the car up yesterday and the idle was so bad I had to take it right back, and asked them to repair. After picking up this evening, the guy said "some vacuum tubes needed tightening".

I drove it later this evening and there still is the unmistakable rough idle/surge at around 700-900 RPM. After that, the car is smooth.

The shop involved isn't very cooperative now and they have me really tee'd off. I suspect they've lost a ton of money on all the labor cost trying to fix the problem they created.

They are now trying to say its probably other maintenance items such as distributor cap or rotor, etc. I'm skeptical since the car idled fine prior to their valve re-work. I don't want to give them any more business than I have to, but I want the car fixed.

Anyone with repair knowledge of the 420 have some ideas on this? Could it just be a "fine tune" adjustment with timing or something vacuum related that is needed? Or something more ominous with how they handled the valve job, etc?

Any thoughts?