Ok, the gas milage in my car has been fluctuating wildly as of lately. Driving habits have not changed and I fill up every 3 to 4 days driving approximately 80 - 100 miles each day. About a month and a half ago, I did a tuneup consisting of wires, plugs, rotor and cap. I changed out the coil because it basically died after doing the tuneup (Thanks to the fine folks who helped me t-shoot it). Tried changing the original ICM to an aftermarket (AZ) one but swapped back because all the AZ one did was make the car die (Go figure, the car is a Japanese American Princess Snob on parts) Also the car has new tires with about 500 miles on them. Idle is a fairly consistant 650-800 with no extreme up/down when at a stop light. So basically the problem is the car can go from 37mpg one fill up to 28 mpg the next and anywhere in between and Im not sure what the root cause is. And oddly enough the best milage I got is by having me + 1 passenger, otherwise, Im driving by myself and not using the AC and the majority of trips Im using cruise control since Im driving to work and its 65 mph commute. I plan on doing the timing belt in the next 2 weeks or so for a weeping water pump. (Car has 60k on the change as of now.) Any thoughts on what could be causing the wild variation in milage?

 

How's the air filter? Has the IACV or FITV ever been cleaned? Tuneup parts were quality parts?

 

Filling up at the same gas station??

Maybe when you are driving +1 you are driving more conservatively?

 

it could be sucking air thru the cruise control valve could also be bad gas do u always fill up at the same station

 

Have not explored the cruse control valve, but have been trying to be consistant with gas station. Air filter was cleaned less than 4k ago (I have a KN), Tuneup was quality parts. Going to be doing a Waterpump change in the next week or so (Timing belt at the same time and will clean IAC and Fitv and do a valve clearence adjustment)

 

^ FYI the 93 Civic doesn't have a vacuum-powered cruise system.