After 3 trips to the dealership, my car is yet to be fixed

Here's the scope:

Last week I took my car in for cel's 171 and 174 after unsuccessfully looking for a fix. Turns out they said they found a leak somewhere in the vacumm lines. Well, the CEL kept on coming back. Tired of them I took it to a local car shop and they said it was the sensor next to my airfilter box. We had that replaced. However after driving the car within 20 miles another CEL came up with the codes P1519 IMRC Stuck Closed. They said it was probably the computer in the car that is messed up or the IMRC which would cost an arm and a leg.

If it was indeed the IMRC, what should I do to make sure it was the proper diagnostics that it is the fault.

Also, all these while(during the CEL 171&174 period and now the P1519) my car would stall everytime I hit a red light. RPMs would drop down to 0-500rpm range and stall.

My car is an ATX Contour 1996 SE v/6 with 110K miles on it.

Thanks