The problem with this is that it can be many things ! It can be one of your 2 O2 sensors (common problem, in this instance I think oem parts are best...) but many other things as well. A diagnose needs an appropriate tool that not everybody has. You could get an odbII one (depending on your car's year) for +/- 50 - 150 USD on ebay I would think.
I would perhaps first think of changing the O2 sensor(s) if they haven't been changed for a long time ...
Good luck !
I would perhaps first think of changing the O2 sensor(s) if they haven't been changed for a long time ...
Good luck !