Pull the throttle body as the mechanic suggested clean it throughly and ALSO clean and/or replace the idle control valve in the throttle body. I had been experiencing similiar problems for nearly a year. I replaced all the O2 sensors, purge valve, MAF, MAP, throttle position sensor and analyzed all systems and still the problem persisted. I cleaned the throttle body and idle control valve and the VX runs better then it has in over a year. No stalling, no erratic idle. I later replaced the idle control valve with a new one, about $45. From what you are saying, I would put my money on the throttle body and idle control valve. If you are concerned about the intake manifold gaskets, have a mechanic smoke the engine and it will tell you if you have a vacuum leak.