Report "My 1991 cavalier 2.2L runs and starts fine at all times but i have noticed once it is warmed up my oil pressure goes right down to 0 and my "CHECK GAUGES" light comes on when i hit the gas it goes off. it also twitches sometimes when im sitting at a light but my cavalier runs fine............ im thinking it might be my oil pressure sending unit. where 'bouts is that located and how easy is it to change? thanks for ur time. Dane"