Hi I have a 95 buick riviera, supercharged. I have a problem that only happens occasionally. The car will crank over but will not start unless I pump the pedal or floor it. Also sometimes the car will stall while I’m driving. I pull over and the car will start right up. I’ve changed the battery and ignition module, still have the same problem. Today the car wouldn’t start so I had it towed to the mechanic. It started right up. They said there are no codes on the computer. I’m thinking fuel pump but mechanic said the fuel pressure is right. I’m trying another mechanic; also switching to preminum gas but if anyone has any other ideas please save me from banging my head on a wall. Car has about 225,000 miles.
It sounds like there’s two seperate problems. A starting issue and a drivabilty issue.
For the starting issue, the problem might be with the Idle Air Control valve. This component allows air into the engine so it will start and idle. If this valve fails to go the proper position during starting no air can enter the engine to start the engine. When you step on the accelerator during starting it opens the throttle plate in the valve body so now air is able to enter the engine and the engine starts.
For the drivabilty issue, have the Crankshaft Position Sensor tested. This can cause the engine to stall while driving or not start.
Mechanic is thinking there is a bad sensor or wire in my ignition harness. I also have a bad camshaft sensor but he doesn’t think that is the whole problem. It took 2 days of my coming back for computer testing for us to figure that out.