In another post I stated that the gas mileage of my 1996 E320 dropped from 21 mpg (which was already not the best) down to 17 mpg in mixed driving 35% city 65% freeway.

According to many tips from the forum I have replaced thermostat, air filter, spark plugs, ignition coils including ignition cables, O2 sensors, MAF (after cleaning the old one did not help) with no success.

Last week I did the following jobs:

- Fixed the auxiliary fan so that now both fans work fine instead of one.
- Changed the airfilter, although it still looked very clean with just 5000K.
- Tightened the air intake temp (AIT) sensor, which was a bit loose because a clamp was broken.
- Changed the oil with 5W-30 synthetic (instead of 0-40W).

The good news: suddenly I got again 21mpg like at the beginning of my possession. The bad news is I am at a loss as to which of the fixes above is the main contributor or the sum of them all?

My suspect is the AIT sensor, your guess?

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1996 E320 since 1/16/08, 171K miles as of Feb 2011

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1989 300CE - R.I.P. Dec 29 2007
Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE