Over the limit on what?
Actual numbers for these would be helpful
If it backfired your timing belt may have skipped.
High NOx numbers means EGR system is not working right, if so equipped, or you are running lean if no EGR, with either you are probably "pinging" under load.
An important part of emission output is the engine temp, that's why "they" recommend driving vehicle for 20mins prior to bringing it in for testing.
2.3l tends to run cool which is very bad for the emissions and the engine.
It should have a 195degF thermostat and engine temp on gauge should be above 1/3(just below 1/2 is best) after 5 minutes of running.
If engine stays cooler then emissions will be higher and oil will never get warm enough to burn off water(condensation) and fuel(blow-by), this will cause bearing damage if left unchanged.
Standard cold startup on fuel injected, computer controlled, engine should be like this:
Engine starts and idles at 1,000rpms, a little higher if outside temp is very cold
As engine warms up idle will slowly drop
At normal operating temp(about 5 mins) idle should be at 700rpms and stable.
If idle isn't stable and tends to go up and down, then MAP sensor on firewall may have a leak in it's vacuum line, MAP sensor is a small device with a 3 wire connector and a vacuum line connected to the intake.
The MAP(manifold absolute pressure) sensor is the main sensor the computer uses to adjust the gross fuel and air mixture, O2's are used for fine tuning, but ONLY after engine warms up, O2's need to be at a minimum of 650degF to work.
So a mis-functioning MAP will cause rich/lean problems, so emissions problems.
Last edited by RonD; 05-06-2014 at 11:18 AM.