HI, would like to say hello.New to this forum. My old mint condition 91 Grand prix has developed starting,and intermited stalling problems. Ok Hard starting runs rough at start up like stumbling ,like starving for fuel. also stalls on highway or after parking. "This what I have done so far:Changed fuel fiter, iac sensor,tps sensor, air filter,crankshaft sensor/took it to shop ran diagnoitic check NO CODES, they said they put noid light on fuel injector line it did not light said it was crankshaft sensor. Drove it home stalled at park later. After pumping the hell out of it started at 13 times of restarting,drove home. Shop towed auto back in.Called me up said it has a vacume leak at lower manifold,wanted $575 to replace. towed auto back home. "QUESTION COULD A LOWER MANIFOLD LEAK CAUSE HARD START ALOT OF VIBRATION.AND STALLING. Need some expert advice on this one would like to get my toy going again."Thanks for help..