Hey, I've got some questions for you B18 people in here, hoping someone can give me some suggestions or possibilities as to whats wrong with my car!

I've got a 94 'teg LS Automatic with 120K on the clock. The car in the past had been getting hot, so my mechanic replaced the radiator. Not long after that, the car still is getting hot, and is also surging while idling between 900 ~ 1500 rpms, consistently. Now, I think my mechanic is a crook, but he told me that I had a crack in the block, or a cracked head, or a bad head gasket or something of the sort which is why the car overheats. I noticed some areas where it looked like coolant had leaked and dried on the hose from the radiator to the engine, and I don't know if that was from before or now (I don't see anything new after running it, though). The oil isn't milky, the motor sounds fine (aside from the surging) and it's not leaking anything under the car as far as I can tell. But, because of this surging and the temperature getting hot, I don't drive it until I can get a proper diagnosis (my crook mechanic said it wasn't worth fixing or I should just get a new motor). Intuition tells me that it's possibly a sensor (for the idling problem) and a radiator/thermostat/etc problem for the engine heat issue. I know that heat is the worst for a Honda motor (killed a Subaru with overheating the motor), but I need some ammunition as to what the problem may be so I can have another (hopefully more reputable) shop look at it.

Please, any suggestions as to what the culprit may be, and how involved fixing it will be?

Thanks!!!