Clyde,
I was under the impression that you had removed the throttle body. I would highly recommend that you do that and clean it very throughly. Take the idle air control valve off and use the same throttle body cleaner to clean it throughly and reinstall. What was happening to me was the valve was sticking open and allowing excess air to enter the engine. I was getting a P0101 code which is a problem with the MAF system performance. This code does not however indicate that it is the MAF, it could be a number of things, TPS, MAF, vacuum leak, MAP, or any unmetered entering the engine.

I had been dealing with a problem you described for over a year. Three different mechanics and I tried everything, but the problem was the idle control valve, which I found on my own. Try cleaning it and see if the problem does not improve. If it does, order a new replacement.

As far as the problem with intake gaskets. It was a problem with the material they were made of, nothing to do with the casting of the manifold. The later gaskets were made of different materials and that seems to resolved the problem The older would become brittle after time and temperature and crack.

The clunk is pretty common in all the VX's and I don't believe that it has anything to do with your idle and stalling problems. I did change my fluid in my trans, tod and differentials to Royal Purple and it has made them much quieter and run cooler.