I have a 91 Lesabre with 57,000 miles that flashes code 42, but it is intermittent. When I go to work in the morning, no check engine light, But when I start it to go home at night it will come on. If I shut engine off then start it again sometimes the light will go out and it runs fine. Even with the light on it starts and runs ok but is little rough. Does anybody know what will fix this? Is it the camshaft pos. sensor, the crankshaft pos. sensor? ECM?