97 sl2 drop in mpg

my 97 sl2 has ran great and I just hit the 160k miles. I use to get
27mpg in the city and 35 to 37mpg on the hiway but recently something
has changed. My mpg is now about 24-25mpg on the hiway and 20 in the
city. Pu new plugs in as normal (twice a year) but that didn't seem to
mke a difference. Over the last 2 years the car has had new plugs, new
cts, new air filter, changed oil every 3months, new tires and struts
all around, upper motor mount and the sensor that is up front by the
air intake. ( it is actually the same one as the cts ). and finally
the forward o2 sensor.
So where should I start looking to find out why the drop in mpg's. I
did notice that when I changed wires that 3 terminals were very
corroded on the same coil ( or whatever they are called) which a
cleaned and buffed off then put conductive grease on them but noticed
that they had corroded up again after about a year. The other set is
nice and clean and always has been so. Is that a coil problem with
that pair or just something that happens. I really guessing at this
time so please point me in the right direction.
Phil

 

sorry I meant 2 terminals ( actually 1 and 2 on the coil)

 

YOu did not say where you live but MPG can drop a good bit in winter
in some areas due to temps and alchol in fule whigh lowers BTU
content and there for MPG. You might check the ECS because if it is
bad and keeping engine rich, MPG will suffer.

 

Thanks snowman.. yes I live in wisconsin but other years it didn't
drop that much and this has been a very warm winter. Is the ecs the
same as thecoolant temperature sensor.. oh I also might say that I had
the engine thermostat replaced (saturn) but that seemed to make it
worse but the engine does warm up faster now and maintains a better
temp in the winter.

 

Yes it is the same and if it has never been replaced (ECS) you should
consider it because if it is bad and telling PCM that engine is cooler
than it is, it will run mixture richer. ALso on the alchol thing. Not
sure if it applies to WI but oil companies stopped using MTBE in fuel
about a year ago and replaced it with alchol which lowers BTU content
of fuel.

 

So where should I start looking to find out why the drop in mpg's.

The very first thing should be to read the stored codes. They may tell you
the answer without having to replace any parts that aren't to blame.
Autozone and other parts stores do it for no charge.

Lane [ lane (at) evilplastic.com ]

 

it has never thrown a code and my codereader never showed anything.

 

Havent followed the thread but a real scantool would be a good thing to
hook up to pull some actual sensor values. Some things like a ECT sensor
could be out of range and the ECM probably wouldnt know it...