The door locks are vacuum operated, and you've got a pump problem or line problem.
The AMM would cause your jumpy idle, but since the Check Engine light is on, just have the codes read, and that'll point you in the right direction. Could be O2 sensors, etc. On this year of W202, it could also be a degrading wiring harness.
With the AC and the vents, it might be a air direction flap problem. Make sure the vents are "open" before searching farther.
1998 C230 "Black Betty"