My car is only getting about 200 miles per tank. just bought car so don't know much about maintenance history. What should I check? Also, vibrates like crazy at and idles at 500 rpm. Any suggestions? Thanks

 

If gas mileage is not too bad, don't be too concerned about it.
Old car just use more gas because of their worn out engine parts.
You have to rebuild/replace everything to get the same gas mileage.

So many things to check. Here are a few things:
Check and replace spark plugs.
Check and replace fuel injectors.
Replace dirty air filter.
If your engine can't reach its normal operating temperature, replace the thermostat.
Check and replace the O2 sensor.
Check and replace the Coolant Temperature Sensor.
Clean the EGR valve, and check to see if this system is working.
To get better gas mileage, most automatic cars have whats are called torque converter lock up clutches. This clutch must engaged at 40 mph or so to lock up the torque converter.

 

Many times, it's the bad motor mounts that causes the car to vibrates.

 

Yeah, just changed spark plugs. O2 sensor is bad, and I'm pretty sure motor mounts are too. Will check on other things, thanks!

 

Our cars have EGR valves?

A bad O2 sensor WILL give you bad gas mileage, and if an O2 sensor is bad, check the catalytic converter as well.

 

Yes, Dodge Neon cars have EGR valves.
I found mine somewhere.
You can find it by finding the metal hole that runs from the exhaust manifold to the egr valve, and there is another hole from the erg valve to the intake manifold.

 

what else causes vibration?

 

Rough idle

 

Misfire, worn/torn motor mounts, IAC out of whack...

 

Really? Where? Only a few early 2000 Neons had an EGR valve, as well as 1gn Neons.