Hello everyone,

I have a weird problem. My 95 940 usually averages 23 MPG. It has been around that since I started keeping track (with Automotive Wolf) 3 years ago. A few months ago, my engine started sounding a bit like a tank. It started softly only heard during hard accelerations (like freeway on-ramp) but over a few months became much louder with even minimal acceleration (like making right turns from stop). During this time, I filled the tank 3 times, each tracked to approx 26 MPG. I took the car to San Diego Volvo because the noise was a bit annoying and they diagnosed a exhaust gasket leakage and found an air mass flow sensor error on the computer ("code stored in computer" even though check engine light was not on). $800 later, after they fixed the gasket and replaced the sensor, my mileage dropped back to the 23 MPG baseline on all subsequent fill-ups. What's going on here? Fixing 2 faults made the gas mileage worse?

On another note, my car was at 179k and there was no way I'd give SD Volvo another $700 for the 180k maintenance. I increased my MPG from 23 to 25 MPG after I:
1) Replaced air filter with new K&N filter ($40 from Kragen online)
2) Mobil 1 Synthetic ATF flush ($5.50/qt after 20% off coupon)
3) Valvoline Synthetic motor oil change
4) Mann oil filter change (from IPD)
5) Bosch distributor cap and rotor replacement (from IPD)
6) Spark plug replacement with NGK plugs (from IPD)
7) Spark plug wire replacements with Bougicord E class (from IPD)

I think the MPG increase was due to the K&N filter, but I can't exclude that it was from one of the other changes. Here are photos of the old plugs and wires I replaced (notice I shattered the original rotor trying to pry it out using a screwdriver):




Comments on the combustion residue on the old plugs? They seem pretty good to me. They were from cylinders 1-4 counting from right to left.
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'95 940 non-turbo sedan @ 175k miles