I have a 93 Cherokee Sport with a 4.0L and an AX-15 manual and have several odd issues like I haven't passed smog even after a tune up, replaced the 02 sensor, replaced O rings on the fuel rails after finding a vacuum leak on the 6th injector, replaced coolant temp sensor and thermostat after a OBD1 scan showed it running too cool, and even injector cleaner, I'm also in California so It's even harder to pass smog. Also, I have an odd idle when I rev in first, it comes down to a regular idle for a sec then revs back to 1000 rpm on its own for a couple seconds. With all of that, I also have a bit of a misfire. I do know that I have a crack right before the O2 sensor. I have patched it and hope to replace the part with another one I bought but I would like to know if any of the apparent problems also stems from anything else.

Also New to the forum, so thanks from cali!