P0422 Diagnostic Code

[sagacity]

I just bought a 2000 Hyundai Elantra and I am continuously having problems with it. The check engine light comes on and it reads the P0422 code, which is main catalyst efficiency below threshold. In addition to this code, when I am stopped, my car idles high at times, the needle fluctuates between 2000 rpm and 1500 rpm. and I am getting horrible gas mileage. 85% of my driving is freeway driving and I'm getting about 24 mpg, it seems to get worse everytime I drive. Could all these problems be related? I don't know if replacing the oxygen sensors would do the trick or if it's really the catalyst converter. If anybody can help me figure out what's wrong, I would greatly appreciate it. Thanks!

[beancounter]

I can't help you on the code, but I have a suggestion about the low MPG. Mine was getting kinda low, maybe 23-24 on the highway. This week I drained ALL my fluids and added new fluid to everything, did an oil change, put in new antifreeze about 2 weeks ago, and this weekend I drove 500 miles and averaged 31MPG, which included a 45 minute traffic jam in Raleigh and some slow moving downtown traffic.

My car did idle high a few years ago, then it just decided to stall instead. New set of spark plugs and connectors did the trick on that one.

BTW, I'm also driving a 2000 elantra

[luvsvettes]

Originally Posted by sagacity

I just bought a 2000 Hyundai Elantra and I am continuously having problems with it. The check engine light comes on and it reads the P0422 code, which is main catalyst efficiency below threshold. In addition to this code, when I am stopped, my car idles high at times, the needle fluctuates between 2000 rpm and 1500 rpm. and I am getting horrible gas mileage. 85% of my driving is freeway driving and I'm getting about 24 mpg, it seems to get worse everytime I drive. Could all these problems be related? I don't know if replacing the oxygen sensors would do the trick or if it's really the catalyst converter. If anybody can help me figure out what's wrong, I would greatly appreciate it. Thanks!

is this the only code that ou are getting? checked for vacuum leaks?