I have a 2002 S type 3.0 and when I hit about 40mph the car starts to sputter a bit. It happens all the time. I did get a check engine light and it pointed to the catalyst converter. The car only has 67,000 miles. I recently had to replace a coil.

I don't want to spend $1,000 on coils and plugs plus $500 on a catalyst converter when it would just be guessing. Any suggestions?

 

Get more data (via OBD). Look at fuel trims (hot engine) at idle and then rev to 2000-2500.

May be coil(s), air leak, etc - but the data will rule some out and save you a lot of money.

 

I think the code pointed to the right catalyst. If I keep it at 2000 rpms when I drive it runs fine until 40mph. If I have it in park and Rev the engine it is fine.

 

Post the DTCs here for advice. Guessing and just replacing parts may, or may not, not cure your situation.

Under no circumstances is the vehicle to be operated under conditions that cause the MIL to flash. A flashing MIL indicates catalyst damage

 

It finally threw up a code and pointed to Coil #5. I replace 5 & 6 plus the 3 plugs on that side - runs like a champ!