1996 Corsica runs rough just after start-up

I have a 1996 Corsica that has an intermittent problem.

Occasionaly, just after starting the car, the engine runs rough and is very sluggish for 20-30 seconds. After 30 seconds or so, everything goes back to normal and the car runs fine.

It happens once or twice a week, and seems to happen more often on a hot day after the car has been running, turned off for less than an hour and started again.

My mechanic suggested replacing the intake manifold gasket, but earlier this year when he replaced my intake manifold gasket on another car, the problem turned out to be a bad crankshaft sensor and I am nervous about paying for unneccessary repairs again.

I’d get another tech to have a look and get his/her opinion as well.