I have 2001 SL1 and I have been noticing lately since July of this year that my fuel mileage has been going down. I use to be able to get 100-110 mile to a 1/4 tank. Now I am lucky to get 50-70 miles to a 1/4 tank. I have replace the following parts:

Spark plugs
Fuel Filter
Spark Plug wires

The other think that I have noticed is that every once in a while the car will die shortly after I start it. It seems like the engine is being choked and i have to press on the gas to get it to start. I am working on checking the fuel pressure to see if that is the issue.

If there is anyone out there that knows what i could be, please let me know.

 

replace ects (coolant temp sensor) AND connector.
Source parts from GM dealer

 

Try some Techron fuel injector cleaner in a tank of gas too. Have you ever cleaned the throttle body?

 

Check your warm idle speed, if it is over 950 rpm, then you may have an issue with the intake manifold gasket around the #1 cylinder.

 

mine was doing the same thing and i replaced the ect and it fixed it for me got it autozone for pretty cheap to.Derf has good advice take head to it.