really bad gas mileage? check your spark plugs, fuel filter and air filter. Clean your Maf.
Your idle air control valve controls how your car warm's up, it sounds like that is working as RPMS won't recede until temperature come's up in the block (causes higher compression in the cylinders and more vacuum pressure inside the engine) but you can clean that if it is stuck open a bit your car will dump fuel to keep things running smoothly. same deal with a dirty throttle body
Check all the rubber hoses connecting your intake, these are 16 year old and if they have a leak they will be adding air to the engine that the MAF does not see. your 02 sensor will see that and will force your car to add fuel to reach a more stoichiometric burn.
(you can spray carb cleaner on the hoses, Listen to a increase in RPM while spraying if the idle changes, the hose has sucked up some carb cleaner which is a fuel caused the rpms to change... then its simply replacing rubber with silicone hoses, I reccomend buying some small zip ties to get everything as tight as possible.)
it doesn't make sense that your 3400 @ 70mph and other are at 3050. I would compression check the engine at the same time as checking the spark plugs to rule out any major headaches right away.
Last edited by Bassnectar; 03-10-2013 at 12:46 PM..