I have an older chevy s-10 blazer with a 4.3L engine in it. I believe it is a 92 because it has a fuel injected vortec but i cant remember the year. The problem is that the engine will rev up and down once it is started (from idle to around 1500 rpms). I replaced the intake manifold gasket thinking it was sucking air from around the the gasket itself, and it did not help. Also if you put it in gear it wont move unless u have your foot on the gas, and it will still rev up and down. Please help! thanks