2003 Grand Marquis LS sluggish performance
 

Regarding a 2003 Grand Marquis LS with approximately 100,000 miles that has been regularly maintained by a shop mechanic for the last 6 years.


This car's acceleration has been sluggish for quite a while now - 1 year +.


In the last few weeks, the problem has grown worse by graduating from sluggish acceleration to chugging.


When adding fuel treatment, the sluggishness and chugging is reduced significantly. However, when the fuel treatment is used up, the poor performance returns.


The last tune up, 6 months ago, has failed to solve the problem.


Other than avoiding that mechanic, where would be a good place to start to diagnose the source of the problem ?

Check out the cat. converters in the exh.???
Injectors may be not operating 100% maybe a complete fuel injector cleaning...