I wouldn't blame the dismal mpg on the new ETM, but a careless mistake by the mechanic. Check the vacuum lines around the throttle body area and see if one of them is loose. Check the electrical connections for the same.

Usually, when someone reports such poor mpg, the front O2 sensor is going bad and can be detected by a good scanner. The dealer will start throwing parts at the problem, you need to find out first what the real problem is.

Go to an autoparts store and borrow a scanner, turn the engine on and watch your O2 sensor for bank 1 position 1. It should fluctuate rapidly between .2V to .9V. Also check for codes that are stored but haven't reached critical mass to turn the CEL on.

Klaus
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Volvoless. Sold the R. There is now a void...