I have a 1990 gmc k1500 rich smell poor gas mile.

1.) The line you cleaned, was it the solid to soft one from the drivers side valve cover to the back of the throttle body to air cleaner spacer. Some oil in there is fine, as your engine wears out you get more blow-by past the pistons. The engine draws the waste gas in through this tube to be burnt, for emissions. 2.) Is it just the smells and lower fuel economy or did you notice a power loss? Your timing maybe out, how careful where you to get it back to exactly where it was before? 3.) What did you use to seal the valley, flat area on the block between the heads. The rubber pre-molded gaskets or the old school bead of RTV. Even with the pre-molded I use extra RTV where it meats the intake gasket on the head. You may be leaking oil vapor from this area check with a mirror.

I redid the intake manifold gaskets again and it was leaking again (looked like from where you put the distributor) so I took it out to take a look and readjust and when I put it back to see if I fixed the problem. Not when I go to start the car the starter starts to crank and then a pop happens with distributor. What could cause this?