Thought I'd share a recent experience:
Back in November, I bought a new air filter for my 89 260E and when I tried to replace it I discovered that one of the air filter housing nuts had seized and I could not unscrew it. So I left it alone and decided to take care of it "later."
Months when by and "later" never came, and during that time I noticed the following:
* My engine temperature was always well below 80
* I would spew a bit of black smoke on hard acceleration
* I would occasionally notice a rotten egg smell when lifting my foot slightly off the accelerator
* I was constantly buying gas -- mileage had dropped to about 12 mpg -- and spending an extra $20 per week on fill-ups.
* The car had a general feeling of sluggishnessness, and the engine would rev and strain a bit too much, and too
loudly, on standing starts.
I did not consider the air filter connection until this past weekend when after the fuel needle indicated "empty" for the second time in about four days I decided enough is enough and pried the offending nut loose.
The filter was incredibly dirty, and I cleaned out the metal housing (sand had accumulated in some areas) and intakes, replaced the filter and noticed the following:
* My engine temperature was back to just above 80 -- where it belongs.
* I do not see any more black smoke.
* I smell no more rotten eggs.
* My mileage is back up to 28-30 mpg (highway) and my wallet is very happy!
* Driving is once again spirited and energetic, with no strain on standing starts. The car can breathe again.
Evidently, my car was suffocating and these were all side effects -- the worst being the approx $700 wasted on unnecessary fuel because I did not take care of that seized bolt right away.
It's amazing how something as seemingly trivial as air filters can have such profound effects, and I recommend keeping yours as clean as possible. ($40 every couple of months is a lot cheaper than $700!)
[Edited by EricSilver on 07-10-2001 at 01:19 PM]