I have a 94 Bonneville with an "L" code 3800 engine. The check engine light comes on regularly. It often comes on within a few seconds of starting the car. Other times it comes on after it runs for a while. It may be off for two weeks at a time, but is on more than it is off. The code is cam sensor failure. I have replaced the cam and crank sensor. Changed the plugs and wires. When the light is on the engine misses periodically. 99% of the time it is barely noticeable only when you take your foot off of the gas. Other times, I will be driving at 70 mph. After 30 minutes or so, it looses all power. It misses and acts as if it is being starved of air. If you press the petal down until it downshifts, it will start to act normal and accelerate. It loose power again once you let off of the gas. This will go away after a couple minutes. It has 156,000 miles. The exhaust is original, but does not seem to be bad. It passes the states exhaust gas certification with very good results. I do not see a difference in the gas mileage. Once in a while I notice a pressure build up in the gas tank. It will vent for a few seconds when the cap is removed. This happens mostly after driving for an hour with a low gas tank. Any ideas. This thing has been driving me crazy for the last year.

Thanks