Hi I have a 1998 Civic EX sedan 5 speed manual. I am seeing that fuel economy is not being too good.

I changed:
Spark plugs
Spark plug cables
Rotor
Distributor cap
Air filter
And left my Iginition timming at 14° BTC


I am roughly getting 23 mpg in combined driving. Car runs fine, I am seeing that my idle stays at 1400 rpm when coasting on netral.

Is that timming the best for economy? I know it should be 12 +-2 BTC

 

You can't adjust timing without some sort of engine management software and tuning...


Even though you have advanced it mechanically, the ECU is retarding the timing to where it should be.

Set it to 12 degrees... The red mark..


And don't coast in neutral, your burn more fuel.

 

Try seafoaming your car, then doing an oil change after. Could be that you have a build up, did it to my truck last week and my mileage went back to what it should be.

Usually when I seafoam I put 1/3 in the tank, 1/3 in the oil cap and 1/3 through the brake booster, then after 500km I do an oil change and then usually the car runs like it should.

 

1400 rpm is really high for idle. Check for vacuum leaks.

 

Listen to ddd4114. Your car shouldn't idle that high. My d16 idles at 700 revs when warm. That could play a part in your bad fuel economy. Sitting at stop lights turning that many RPMs is using twice as much fuel as it should.