I have a 97 TJ that I bought earlier this year. Before I bought it the catalytic converter was removed and a straight pipe was welded. The car runs fine when the temperature outside is 45-90. When it get into the 30s or lower it starts fine but feels like it is misfiring while driving. It jerks like its missing and at idle the RPMS slightly increases and lowers back and forth. I was told by the previous owner that it is because it doesn't have a CAT so the post O2 sensor isn't doing its job. Does anyone know if this is what the problem is or if it could be something else. Thanks for the help.