is it tune up time? 89 300ce 68k
 

i purchased a 300ce about 11 months ago all original,it had 65k on it and now has 68k,it runs pretty good other than a bad eha valve,im wondering though should i replace the cap ,rotor, and plugs now,i know it couldnt hurt right? i was reading allot on here about resistor/no resistor plugs,whats the difference,i was thinking of bosch platinums,whats a good plug for a 103 engine 1989,thanks guys.oh is 300 miles per tank of gas ok? i noticed when i regapped the plugs it ran a bit better.everything is original,plugs wires, cap, rotor, plugs.

Welcome to the forum, looks like you got a nice low mileage 300CE there!

Spark plugs: gap to 0.032", do not use platinum plugs, they do not run well in these era of engines... go with Bosch or NGK non-resistor plugs

As far as cap, rotor and wires, I would go ahead and do them due to the age of these parts. ceramic becomes brittle, wires start to arc, etc. However, if you replace these parts and it makes no difference in performance or economy, just keep them as spares or put the old ones back on and keep the new parts as spares.

I think the 300E/300CE tank capacity is 18.5 gallons,
so 300 miles / 18.5 gal = 16.21 MPG with an actual figure a bit higher since you are not completely draining the tank every time... seems a bit low, most people seem to get about 20 to 25 MPG with their cars...

A refresh of those items won't hurt and will give you a good baseline. I recommend the Beru wires with Bosch cap & rotor. Whatever you do, don't go with platinum plugs. The M103 series engine really doesn't like them.

miozzi, I also recommend using Beru spark plug wires and Bosch distributor cap & rotor. You should also replace the distributor cap O-ring seal because it's probably dry/brittle.

The spark plug specified in your Owner's Manual may no longer be available. Suggest calling the Parts Department at your local MB dealer and ask what spark plug they recommend for your 1989 300CE. You definitely want to use a copper core, non-resistor spark plug.

The most I have ever filled up to in the last 3 years is 16 gallons. Even after driving on the light for 30 odd miles..

Before I moved here to AZ and use A/C all the time, I averaged 20mpg 400mi on a tank. I unfortunately only get 15-16mpg now :(

As stated above, being proactive, especially if you think they are original might be a good idea. You may even find your fuel economy and power will improve. Stick with OE items and you will save yourself time and money in the future.

Definitely look at the idle control valve vacuum hoses. If they are rock hard, replace them!