Got this code last week, it cleared on its own (but I checked to find out the code anyway), then today it flashed me the code again. Here's the confusing part: Recently (last 2 tanks), I've experienced a marked INCREASE in gas mileage. You read that right, my MPG has IMPROVED. I had chalked it up to replacing the stock soft top with a frameless, thus creating a bit less wind drag. Now with the code, I began to wonder, so I checked the symptoms only to learn I should be having the OPPOSITE issue. So, if I get this fixed, am I going to drop from my near-18-MPG back down to my more customary 15 MPG? It's a stock 4.0 with 141K on it. I just replaced the muffler last year at about 136K. Any guidance (or explanations) greatly appreciated.