Drop in gas mileage - unknown cause

[TuftsAuto]

Hey all, my 2002 Boxster S has been running at lower efficiency, and seemingly lower power, for a few weeks, and I'm now getting around to chasing down the source of the problem. I noticed that my mileage used to be around 20-23 mpg in the city (27-29 highway) but it has since dropped to around 15 mpg. In addition, there seems to be a slight drop in power as well as a faint unburnt fuel smell coming from the exhaust. There is no check engine light.

Any ideas on how I can chase down this issue? Has anyone had this happen before?

Note that my car did get hit at low speed in the front end a few days ago, but I think that this is independent because the issue popped up weeks ago.

Thanks for your help!

[Gilles]

Originally Posted by TuftsAuto

I noticed that my mileage used to be around 20-23 mpg in the city (27-29 highway) but it has since dropped to around 15 mpg. In addition, there seems to be a slight drop in power as well as a faint unburnt fuel smell coming from the exhaust. There is no check engine light.

Tufts

When was last time you replaced your air filter, spark plugs, etc..?

Usually when you neglect these, the mileage and the performance goes down pretty quick, hopefully is something this easy

[TuftsAuto]

Thanks for the tip. I changed the air filter six months ago, but haven't swapped spark plugs. The car has 77K miles on the body, but the engine was factory-replaced after an IMS bearing failure at ~40K miles (need to look up exact amount).

What is the cost and procedure (time to do at home) of changing spark plugs?

[Steve Tinker]

About 2 hours to replace plugs - cost is minimal as the Bosch or Beru plugs are standard items. You need to jack up the rear of the car install jackstands and remove part of the wheel arch plastic liner + moulding for access to the coil packs and plugs.

A few years ago I had the same symptoms as you, plugged in the trusty Durametric and found the MAF below limits. Replaced and performance + fuel economy back to normal.

[NewArt]

Originally Posted by Steve Tinker

A few years ago I had the same symptoms as you, plugged in the trusty Durametric and found the MAF below limits. Replaced and performance + fuel economy back to normal.

Steve, did that throw a code?

[Steve Tinker]

No it didn't - the only way I found it was by using the Durametric.
The performance had fallen off slightly so I plugged it into the diagnostic port. The big difference was with the new MAF - everything was better (economy + low / mid range performance) it felt like a different car. Who'd have thought......

[TuftsAuto]

Thanks for the tip! I cleaned out the MAF using standard MAF cleaner spray and the car is like new. Improved gas mileage and throttle response. Possibly a bit quicker too.

[Steve Tinker]

Good to hear you had some success.....