Shakes for a Second but does not Stall - 97 Sable
 

I have a 1997 Sable with the 3.0l Vulcan which now has 101k miles. I bought it used with 98k.

Occasionally, when I start the car, the motor feels like it is shaking and sounds like it is about to stall but never does. When I hear this event, I press the accelerator for a second or two, and the event disappears. I have had this problem since I bought the car.

I have replaced the spark plugs with Motorcraft Platinum, the spark plug wires, the ignition coil, the IAC, the Alternator, the Battery, the Fuel Filter, the PCV Valve, and used Dry Gas and Techron Fuel System Cleaner but can never seem to eliminate this occasional problem. I even changed the Fuel Pump Fuse. My mechanic replaced the CAM Position Sensor.

The car runs very smoothly after starting, and accelerates without hesitation or misfire. I have changed all the fluids, and have no leaks. Moreover, the car has been reliable and comfortable to drive.

A friend of mine suggested it is bad gas. I admit, I did fill up at a Delta gas station a few times. Since then, I have been filling up with BP, Shell or Exxon Regular 87 Octane.

I even tried two bottles of Gumout Octane Booster which seemed to smooth out the starting issue but am not sure.

I was wondering whether the new spark plugs I installed, or the fact that the car now has 101k miles has now increased the need for higher octane.

Like I said, this problem is intermittent.

Anyone have any ideas? Thanks

I imagine you check the computer for any codes at this point and there are none. One thing that seems to make any sort of sense is a fuel issue at startup. Seeing the car is fuel injected maybe it's possible the fuel pump is not doing it's job to Prime the fuel system completely on Startup. When you turn the key into the on position you should be able to hear the pump run for 2 to 3 seconds. Maybe it's just not getting the right amount of fuel which will cause it to shutter for a moment but never stall out. Maybe you can try, and I guess I would call it more of an experiment, and try turning the key to the on position twice before starting. At the very least they cannot hurt and possibly rule out a fuel pressure issue at startup. I wish I had better advice for you but it seems like you covered all your bases.