I have no clue the last time the plugs and wires were changed, not the fuel filter. But the air filter was changed in November, and the oil was done 2 weeks ago. Tomorrow I'm going to remove the air box and see if it's dirty, and check and see if it may be a O2 sensor because of the exhaust leak.
How long have you owned the car, and how many miles have you put on it? I would defiantly say plugs, wires and a throttle body clean would help with MPGs majorly.If you have no clue when they were changed, change them. As king said maintenance is the key. You don't wanna run strait at an o2 sensor, I had a bad one and it didn't affect my MPGs much. They are not by any means cheap.
I have owned the car 2 years this August, and put roughly 11,000 km(7000 m) on it since then. My grandparents owned it before I did, and they always had it maintained. I'll have to see when they last had plugs and wires done.
As for symptoms, I feel like it has less power, and gas mileage is also suffering. Other than those two, everything seems to be normal. If doing plugs and wires and Anything else easy to do can be done at my school by myself, where I usually do work to it.
maybe check your fuel pressure, smell the exhaust, does it smell like gas? should be like low to mid 40 psi range with key on, pressure should hold steady too, ive seen issues like this, but nonetheless monitor your temp, idle, drivability, if it lags when hitting the gas i'd almost lean towards the fueling, have it tested, otherwise give it a full tune up, usually always helps, pull your spark plugs they should all look the same. all the work ive done on these were all 3.8's tho 2 2003's and a 2004, should be similar tho.
running hot and Poor mpgs sounds like a clogged cat. Go to an exhaust shop, not a mechanic and have them test the cat. A mechanic isn't gonna have the tool to test the flow of the cat. Its a free test and could save you a lot of money. Running it with a clogged even partially clogged can do serious damage to your engine.
Something else has come up that may be the culprit. One of my friends filled my car up with Supreme gas when I ask them to fill it for me, an I usually run just regular, my AutoMechanics teacher says that might have done it, since I usually use regular I was mixing the two types of fuel. He said it was unlikely but it was something.
I would throw that option out the door if its already ran more than that tank through it. That is highly unlikley tho. Maybe if you were tuned for premium like me and ran regular in it like I just done a few weeks ago, but not being tuned for it I doubt you would notice a huge difference in mpgs. Have the cat converter checked. It's a free test and you can walk in without an appointment. Test what is plausible and free before you let them come up with random "possibilities".
Most of the time a run a mix of 89 and 93 with no issues. I have ran 87 and 93 mixed in the past. Have you filled up anymore since the supreme tank?
I'll check out a muffler shop tomorrow. I've never filled the tank since then, just added $20 here and there, no a lot of gas in Canada. I put $40 in today and it seems to be running slightly better, but I'm still getting it checked none the less