terrible mileage

I have a 97 jetta GL that gets terrible gas mileage. It has been like that ever since I bought it last year, it only gets about 18 to 20 miles per gallon! does anyone have any sugestions to try? I just changed the cap and rotor(which were pretty bad)...didn't seem to help though.
thanks in advance!!

check to see if you have an intake or exhaust leak....could need a fuel filter too

Is it a 2.0? Is the check engine light on? Is the tail pipe sooty or do you see black smoke when you rev the engine?

yes it is a 2.0 and the check engine light isn't on. There is also no smoke or soot in the exhaust. The only other problem i can notice is a kind of rough idle for a few seconds when i first start it up in the morning, it seems to do this more when its cold out too. hope this gives some more help. Thanks!!!!

I'd start by checking the coolant temp sensor. Do you have access to a multimeter?

ya i do have a multimeter, but what would the coolant temp sensor have to do with gas mileage?
I was thinking it might be the o2 sensor but really have no clue!!!
Thanks again!!!!

The ECM uses it to determine the proper fuel/air mixture. Usuallly when the sensor fails it gives a reading which makes the ECM give too much fuel (runs rich). The sensor is located on the water flange where the upper radiator hose connects to the cylinder head. I think it is a blue sensor. The wire colors should be blue & brown/blue. The sensor should read 2000-3000 Ohms cold and 250-300 Ohms @ operating temp. It's a simple check, the O2 can be a little more difficult & would normally turn on a check engine light.

Dude, 18 to 20 is great. Shit I get around 15 or so, I have some mods but nothing fancy. Try 89 fuel instead of 87, new air filter and probably needs a new fuel filter, 18 to 20 is good for a heavy car with a 4cyl, such as Jetta.

I checked the coolant temp sensor and the top set of prongs was 258 and the bottom set was 123 at operating temp. So a little low i guess but would that be enough to cause a problem?

Which was the reading from the two pins that had the blue and brown w/blue trace wires going to them? You also need to check with engine cold.

in my 2001 1.8T i get about 280-290mpt and its got a 14.5 galon tank so... thats like 19.4mpg

I had the same problem. there is a hose in the front of the engine. It runs from the block to the resinator( a spaceship looking thingy). The hose is a hard hose and may be cracked or filled with a coffee ground substance. This problem is pretty common. The hose is called a return breather hose. After I replace it i got double the milleage. good luck!! jett-n