So, on my wife's 94 mercury grand marquis I cleaned the IAC, MAF, EGR Valve and EGR silnoid (?) and the car runs beter thanit has in years. However it still did the engine rock idle fluctuation, durring reving the engine in the drive way I heard this rattleing sound. I turn the car off block the tires and take a peak. The drives side tail pipe seemed to be lower than the passenger side. I grab a hold of the driver tail pipe and it rotates 90 degress. The weld is broken right at the front part of the muffler. Now my question is, durring driving the car, would unequal back pressure cause the engine to idle funny at a stop and cause the CEL to come on durring acceleration? or vise versa? I know I have to fix it, just if this car isn't going to pass smog I don't wanna dump any more money in to it.