My 2003 Grand Marquis is sluggish at low RPMs and has a rough idle. It currently has 124,000 miles. The check engine lightisn't on. The O2 sensors have not been replaced.I have not replaced the PVC valve either ( The aftermarket auto supply stores don't list them). I also have a ticking sound coming from the passenger side of the engine.On that side of the engine itappears that a portion of theexhaust manifold gasket for one of the cylinders has crumbled away. If the exhaust manifold is in fact leaking could that affect the readings of the O2 sensor resulting in the sluggish response? Any other areas that I should investigate.

Most of these problems are solved by replacing your TPS, throttle positioning sensor. Not an expensive item and you can replace it in two minutes as it's easy to get to and only has two screws keeping it in place.

First you need to replace that exhaust manifold gasket and hope that is the ticking sound you're hearing. 124,000 miles means a full blown tune-up, that's including thePositive Crankcase Ventilation valve. Oxygen sensors and Throttle Positioning Sensors are good things to replace if need be, but I would start with the basics. Plugs, wires, fuel and air filters, PCV, etc. . I would also remove and clean your IAC (Idle Air Control) I would even recommend a high mileage oil and a good oil additive. An add to the tank, fuel system cleaner would be a good idea, too.