I have a 99 e320 and lately i have been noticing the car running a little sluggish. When im go over 65mph it runs good. The lower miles its sluggish. Is it time for a tune up? My indicator has not popped up yet telling me to get it serviced? What could it be. Please Advise?

 

If by tune up you mean new plugs then yes. With all the electronic ignitions today, there is nothing to tune anymore. Plugs are a possibility, don't forget the oxygen sensor. My 300E stumbled slightly off the line and a new O2 sensor solved the problem. Bosch has referred in their ads to a new O2 sensor as a tune up. Try plugs first, they are way cheaper than an O2 sensor. I like the Bosch platinum 4, remember these are a 100K plug, if you leave them in for 100K you should loosen and re torque every 30-40K. There have been cases where 100K plugs have fused to the block if overtorqued and left in for the full 100K. Oh btw, my o2 sensor light never came on when mine went bad.

 

Have you checked mass air flow sensor as these hot film sensors are not very reliable and no not show warnings,though may be stored as a fault code.
regards
david (uk)

 

Some anti-seize compound on the plug threads will solve the fusing problem. You can leave them in for 100K without concern if you use some.

 

A bad MAF or bad O2 sensor should light the CEL.

I'd check the air filter and replace if dirty and while you're there, check for obstructions in the air intake stream. Maybe run a can of FI cleaner through the gas tank too--it won't hurt.

 

Good points on the anti seize, MAF may be the culprit but not in my 155K experience, mine was the O2 sensor without a CEL (the 87 did not have a CEL but it did have an O2 light).

 

If your check engine light is not on, I would do all of the regular maintenance stuff before taking it to the shop. I'd do spark plugs, wires if necessary, air filter, and fuel filter.