I have a 2003 Monte Carlo SS with a 3.8 liter motor. I was showing a 0300 code. I changed the spark plugs with all new wires, It then showed a 0135 code. I changed the oxygen sensor and now it is showing the 0300 code again RANDOM MISFIRE. What is wrong with my car. It has a terrible miss to it, What else can I do? I cannot afford to have it towed to the shop because I am on a fixed income. I am disabled and I only get one check a month. WOULD YOU PLEASE HELP ME?

 

Which o2 sensor did you change? Front or rear?

 

Does your scan tool show live data?

P0300 has probabpy a dozen + possible causes (its just a generic misfire code), so we really need more diagnostic data to try to hone this in om an issue. We could suggest all kinds of stuff to clean and replace, but its just shotgunning parts at the problem without doing more diagnostics.

Id be curious what the idle map value is, if MAF is reading consistent, what the front O2 output looks like, what the fuel trims are, and what the individual cylinder misfire counts are showing (ie is it mostly on one bank, just a cylinder or two, etc).