93 Civic VX -only 38 MPG HWY- Do I needd steriods for 50+ MPG?

[benfrogg]

Stock size tires (or at least same overall outside diameter) is important. If they aren't the right size, your MPG estimates will be off potentially dramatically.

Why are you coasting in neutral?
The VX has DFCO that is immediate. The engine is effectively off so long as you are warmed up, in gear, above 1100 rpms, and everything in the car is working correctly. The injectors actually shut off entirely. It pays to downshift and keep it in gear when decelerating.

Erratic idle could still be issues with the IAC, so you could try cleaning it again. My volvo wagon needed to be cleaned and re-cleaned 3 or 4 times before it worked well enough.
The vx will waste more fuel idling in neutral when coasting than if you downshift. The rpms should be above 1000 if you are traveling above any speed but a crawl. This way when you put it in gear your revs are closer to where they will need to be. When you slow to a stop the rpms drop.

Dropping rpms when braking is common. That's a small motor. Any load will cause slight idle changes. Even a brand new IAC and new sensor still wont make it totally stable. Newer technology in newer cars makes their idle more stable than your VX will ever be. Your braking puts a load on the booster as well as your altenator for the brake lights. Both affect idle.

If the car will idle at 650 once warm without loping up and down, you're good to go.

Driving technique is what comes to mind here. Sure, matching tires is what you need. Low rolling resistance will help. A lot of little things will help. Your baseline suggests that driving technique may be your culprit. Accelerating to stoplights/signs is a bad one. There's a lot of helpful info on this site about driving for MPG's.
Weight could be a factor. Are you hauling lots of passengers or ballast?

Learn to feel the change from lean burn to not lean burn. It's at about 1/4 throttle. Shift when the up indicator says so. Sometimes climbing hills it isn't practical, but on a flat plane it should be no problem.

NGK plugs that are listed on the timing belt cover? Those are important.
B

[theholycow]

benfrogg, DFCO is great if you intend to decelerate but neutral coasting is a more effective strategy for certain situations. The situations are generally cruising on level or slightly descending road where you intend to keep approimately the same speed.

[benfrogg]

True, coasting in neutral is handy for certain situations. I tried coasting in neutral all the time and not downshifting and lost MPG's. I assumed 1sthonda had been doing the same. I realize that coasting in certain situations is better than decelerating.
Anyway, all good info.
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[GasSavers_1stHonda]

Wow, this is all great to hear. Thank you so much. I started driving differently. a few days ago. I can tell when lean burn kicks in. I shift when the light tells me, even when it doesn't make sense. 25-35 mpg and in 5th gear, while slowing accelerating didn't make sense at first, but the light tells me it's okay so I guess so right?

I still want to get the timing checked. I think that will make a big difference. I guess I could try cleaning the IACV again. It would be for a 3rd time. (it's really clean looking. The plastic inside it bright white.) I was going to buy another one for a junk yard, but I haven't gotten around to it yet. Is there anyway to tune the IACV? I noticed a little allen screw. Looks like a 4.5mm.

Someone also told me that there's a chance that my RPMS being high at start up was because of a bad coolant sensor. Is this possible?

Also, I have a bad rim on the rear passenger side. It makes the car shake a little. I figured that was causing it to lose MPG.
-Any ideas?

[theholycow]

Originally Posted by 1stHonda

I shift when the light tells me, even when it doesn't make sense. 25-35 mpg and in 5th gear, while slowing accelerating didn't make sense at first, but the light tells me it's okay so I guess so right?

Shifting at low RPM and making use of the VX's relatively plentiful torque by opening the throttle is probably effective for some or all of the following reasons:
- Reduces energy spent sucking air through a closed throttle
- Reduces reciprocation loss (don't forget that the pistons change direction twice per revolution)
- Reduces engine friction, which reportedly rises exponentially with RPM
- ...and whatever else I forgot.

I get my similarly torquey 2008 Volkswagen into 5th at 1000-1200RPM, 25-30mph, and get very good results. Its fuel economy over 35mph is held back by the lack of 6th through 10th gear...

It is common, after discussing fuel economy on internet forums, to think that RPM isn't as important to fuel economy as you'd assume, and to think that the "gas pedal" is what matters...but it's by far the opposite. The "gas pedal" doesn't cause the engine to dump in more fuel than it needs; it just removes an air restriction. Misguided people spend lots of money on less restrictive intakes hoping that they can then restrict it more at the throttle.

[benfrogg]

I agree with theholycow. Low revs and wide open throttle plate for climbing hills instead of downshifting to 3rd and running less than half open. All good points.
I must say, my vx is sluggish at best during this kind of driving. Sometimes I'll get up to 60mph (in a 50 or 55 zone) to try and keep the car in 5th gear all the way up. I also make an attempt around town to accelerate slowly and keep lean burn in all gears once the car is warmed up. I make it to the speed limit, just not as fast as everyone else. This is sometimes not safe but most of our major roads are two lane roads. People can easily pass if they dont like my speed.
The timing on my car was way off when I got it. It was like 1 degree above TDC. Who knows for how long or why. If you DIY, get a budy who knows how to do it. The timing marks are tricky to see on the casing; you line up two marks in the plastic (like aiming a gun) to the spinning harmonic balancer. I marked with a paint marker the grooves on the harmonic balancer before hand.
I went to the most advanced side of factory specs, which is printed on a label under the hood. I can't remember what that number is right now.
This also changed idle speed, which I had to then adjust via the flat head screw on the throttle plate. The more advanced the timing, the faster the idle.
High rpms on start up is to get that engine warm and prevent stalls when cold. It is possible that the coolant sensor could cause problems, but its more likely to cause problems once the car is warmed up. This would cause a CEL and cause the ECU to go into open loop mode which would also likely diminish your fuel economy a lot.
That rim cant help. I don't know about FE, but driving comfort and safety are needed too.

Here's link to my similar quibble. I had the same problem you do when I first got the car. This may shed some light.
http://www.gassavers.org/showthread....ht=vx+horrible

[GasSavers_1stHonda]

Originally Posted by jadziasman

INFLATE TO 37 to 40 psi - What size tires are they and what was the brand

I have some Kumho Power Star 758 on them 175/70/R13. What's the best tire for gas mileage with this car?

[imzjustplayin]

When you guys mentioned tuneup, you forgot the replacement of the PCV valve and the valve lash adjustment.. Also I recommend cleaning the throttle body thoroughly since it'll likely be covered in gunk in all the little passages and under the idle screw. Last thing I can think of is to redo all of your electrical grounds, check the ohms value of them from the ground point to battery ground, getting them to near zero ohms, and replacing your vacuum hoses because by now they're probably rotten and need replacing.