A while back I had a bunch of vacuum leaks with all the normal codes that went with them,I think I let the go a tad to long before I addressed them.I now am saddled with a P0420. I have read all the fixes other than replacing the Bank 1 cat. I read a thread on using lacquer thinner in the tank to clean the cats BUT I can't remember the quantities per tank AND if anyone has had luck with it.I won't hold ANYBODIES feet to the fire for commenting just an honest opinion.I get good mpg in town (21/22) and 29/30 on trips of 100 miles or more.
Problem #2 The only code is P0420. with a permanent CEL. At normal operating temps. low or medium cruising speed She bucks when I SLOWLY accelerate and it DOESN'T downshift. Power isn't great unless it downshifts but if it downshifts all problems disappear, NO temporary CEL flashes just bucks until you let up or downshift or it downshifts on it's own.
Will a lazy cat sensor cause this, a dirty MAF or EGR without setting a code other than a P0420 or IS the CAT bank 1 below spec code the problem. Any thought or comments are appreciated.
PS. I also have a noise coming from the passenger seat that I can make go away by saying YES DEAR I'LL FIX IT! LOL.

 

Awhile back I had a problem with 0420 also. I changed the o2 sensor(The lower one along the firewall. After about 50 miles or so the cel came back on. I then bought a spacer and put it in. No problems ever since. Oxygen Sensor HHO Extension Hydrogen Spacer Test Pipe O2 M18 x 1 5 Thread Size | eBay

 

Last time I had an 0420, I had overfilled the gas tank and not tightened the cap enough.

 

If you are getting a p0420 with no symptoms, the spacer will help take the cel off.

But if you are losing power and your car isn't running well, it may be your cat is bad. You can try a bottle of Cataclean from Autozone for $25, but it is not a guaranteed fix. I would also try Seafoaming your car... it helps clean up alot of stuffs. It is not specifically for the cat converters, but the Seafoam might help with the cars performance.

The cheapest direct fit cat I have seen is on ebay for $200, which is alot cheaper than the dealer part.

 

You most likely have a bad cat. I just posted about it earlier yesterday.

 

Ur cat wants to smoke a joint