rijn

I think one or more of my catalytic converts are bad. I think this for a few reasons. My car (2008 IS350) had a bad MAF for about 4 years which the dealership was unable to diagnose until it generated codes. The bad MAF caused the following for 4 years:

Surging when going into D or R from P (leaping and to aggressively hold the brake)
Unable to hold cruise control set speed when going up a hill. It would drop 5+mph then surge 5+ mph over the set speed
Sluggish throttle response
Transmission would never downshift to accelerate
Mis-fires from running rich and causing pre-mature spark plug wear
O2 Sensors had to be replaced

I've owned the car since it had 10k miles on it and now has 120k. The fuel trim is right on point now, but I can barely get 19 mpg in the city (not driving the car hard) and low end acceleration while improved (new MAF, spark plugs and O2) can be sluggish still. The throttle response did improve dramatically after the new MAF, O2 and spark plugs were installed (not all at the same time).

My gut tells me the cats were affected (as the O2 and spark plugs) from the 4 years of running rich due to the bad MAF. Does this sound right? Is there a method to verify if any of the 4 cats need to be replaced? If so, which replacement catalytic converter brand do you recommend? Stick with OEM, Bosal or another brand?

I do have an Automatic OBD2 reader and use the dashboard iOS app with it.

Gville350

iTrader: (10)

Have budget for PPE headers with aftermarket high-flow cats to pass NC inspections? Also check the midpipe cats.

rijn

Short answer is yes, but don't want to replace stuff for the sake of replacing it. Is there a way to verify the condition of the Cats? I do have new O2 Sensors. Is it safe to assume if they're not generating codes then everything is okay?

Gville350

iTrader: (10)

Visual inspection. But not exactly easy to do so. But you mention running rich, and that is the #1 way to kill the cats real quick. Personally, I'd go with my recommended PPE headers with highflow cats. And while installing those, a visual inspection of the midpipe cats can be done at that time. If condition is good, button up the headers and enjoy the added hp and sound (I've got PPE catless headers with a stock mid and axle back and I LOVE the sound!). But if the honeycomb is falling apart, you can look into a factory or aftermarket replacement midpipe with cats.