I am experiencing some difficulties with my 91 s10 blazer it cranks but won't start if I am patient with it and continue trying (30-40) times it will eventually start each crank getting closer and closer to starting. When I first get in and try to start it cranks and cranks then it will crank fire and die followed by crank fire and run extremely rough and die it and then it will start idle will jump up to about 1200 then come back down to around 600 and stay running. When this happens I can finally drive it and it runs flawless I can even go to the store which is only a couple blocks away turn it off and go inside come back out and it will usually fire back up on the first crank things that I have replaced or that have been replaced recently (before it was passed on to me) are fuel pump and filter, distributor cap, plugs and wires, ignition module, egr valve, coil and I believe the rotor was replaced with the cap "it still has a weak spark but coil tested good with an ohm reader" thanks for any feedback!!! This one really has me stumped

 

Anyone have any ideas????