500E rough idle and gas mileage drop - PeachParts Mercedes-Benz Forum

tom woolner · #1 02-13-2003, 02:52 AM

The last few weeeks, I have noticed my car is experiencing a rough idle, and my gas mileage has dropped to 15 mpg. I have been so busy, I have not looked under the hood for the most obvious answer, a loose spark plug wire. Assuming it is not that, what else might it be? I will take it in to the shop as soon as I have minute, probably next week.

Tom
92 500E 110,000 miles

The Other Mike · #2 02-13-2003, 08:51 AM

When was the last tune up ? Were the plugs changed ? However, I'll bet it is due to dirt in the injectors. In the past I used injector cleaners, but when I had my pathfinder the service advisor recommended that they NOT be used due to the chemical harshness on the gaskets and rings. Was it a ploy to get them to do it ?.

Pool gas mileage is also affected when the outside temperature is below -15c. Don't know if you are experiencing those extremes but believe me the gas mileage of a SUV at -40c ain't pretty.

Smell excessive fumes ? Also check the fuel line with the motor on and off. With it on may be the line from the pump onwards, due to pressure.

Hope my two cents helps

-fad · #3 02-13-2003, 11:35 AM

Greetings Tom-

(on the simple maintence items) possibility(s):
>caps
>rotors
>02 sensor

these singularly or in combo can manifest a rough idle and lower gas mileage

...also, on an outside possiblity- a bad tank of gas (H20 in it or some other nasty-s)

best regards and let us know how it turns out
-fad

placo1 · #4 02-13-2003, 11:45 AM

Tom,

Can you provide a maintenance list of things you've already done. This will help rule out a great deal of items and possibly narrow down the cause.

Just a comment, I just changed my plugs last weekend and I'll be the first to say that the plug wires are very heavy duty and the connection to the plug requires a great deal of effort to remove.