hey Guy, im having a really bad issues with my S type.. Restricted Performance comes up all the time now..sometimes runs smooth and most of the time it runs rough... in between 35 - 55 mpg car hesitates..and misfires bad..

so hear are the things i have done so far.

i have changed the spark plags,
Passenger Cat
Fuel Filter
Air Filter...

After changing the Cat it was ok for awhile and here agian...and today i experienced when im on high way...when i push the gas paddle all the way down..car goes to 3000Rpm and reducing speed right away...i mean it feels like it just wanna come to complete stop immediately ..keep high rav and downshiftting the gears automatically..its like spitting out... any idea whats going on guy?

 

is it something to do with the MAF?

 

Misfires are usually coils - see the many threads about this.

Expect more & worse catalyst damage if not fixed.

 

OK sure i will check them...

 

Coils it is, had that happen on none. Go to the dealer they will replace them all at once...whether needed or not, I have been replacing them as they go bad.
Good Luck

 

If you have not changed the two IMT O-rings, do so now. The factory O-rings were not substantial enough to prevent oil seepage and potential air leaks. The redesigned O-rings are thicker and solve that problem. Leaking IMT O-rings are also a cause of misfire issues, so be sure to change yours pronto. There are several good threads here that instruct you how to do this. Use the search function for "IMT O-rings short route" and you'll quickly receive all the information you need to do this in less than an hour. Tip: the smaller your hands, the quicker you can do this....

 

Get the codes read and post back here. Free at most auto parts stores.

As was posted the 6 cylinder cars have a list of common problems. The good thing is none of them are too expensive. All those problems are well documented on this site.

At this late date (Your car is now over 10 years old) I would plan on doing some maintenance.

Change the plugs and be prepared to change the coils too. If oil is found in the spark plug wells then change the cam cover gaskets and spark plug well gaskets.

Don't forget to check for the dreaded vacuum elbow failure and for sure change the IMT O-rings as mentioned above.

You also should be preparing to service the transmission fluid and pan/filter but first get the car running right.
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yeh i will get the codes..but my question is..when im on highway doing 70pmh...car is smooth..at the same time if i push the gas peddle all the way down...it just breath hard and
3000 rpm and car slows down...do u think its coils? and 35- 55 it hesitates ..

 

Stop trying to guess.

 

I guess you are right JagV8... im gonna change the coils and let you'll know whats happening.