OK if you mean by guide pins, they are 2 pins on each side, 1/4" diameter IIRC, that are in the decks of the block, and stick up maybe 1/4" or 5/16". If they were gone, then you woulda known as you woulda had to do something to hold the head gasket in place while you dropped the heads in place (like glue them in place or put a couple of head bolt through the head and gasket to line them up). Maybe the pins pulled out with the old heads? Others ought to comment (so you don't pull the heads for no good reason!) but I would not expect any guarantee for the heads to align properly; the head bolts can't be counted on alone for proper alignment IMHO.
But hold on a minute: If you did install it 1st time with no coolant leaks, then I am starting to doubt that this is the issue. What engine is this? If you have a vacuum leak on a carburated engine, a high idle is not what you would get so that is perplexing too.
FWIW, I am not following what are the intake aluminum guide sleeves....???
