Hopefully I remember this long history correctly. I am used to getting an average 40 mpg with my 2000 Civic LX with 94,000 miles. Recently there have been some strange problems. I changed plugs and wires several months ago, and that may be the beginning of the trouble, but I'm not sure. The mileage actually went up a bit after that. Then I noticed that the engine would catch now and then, especially at low RPM like a second gear roll-through. I suspected a fuel line problem and ran some injector cleaner through the system. Then the engine light came on - O2 sensor, and probably because of the cleaner. Anyway, I installed a new Bosch sensor, pulled the negative terminal to reset things, and eventually the check engine light went off for good. Mileage was around 36ish. Then I replaced the fuel filter, and the next tank of gas was down to about 32. That is apalling. I guess it makes sense if a clean filter is letting through more gas! I pulled the battery to reset the ECM and the car ran smooth, but slowly got worse again. Then I reset the ECM by a method described in another forum, by pulling the fuse, replacing and letting the car idle etc. Again, the car ran great, but now it is getting worse again. It's almost as if the computer is incorrectly adjusting things and making them worse than the "default" setting rather than better. Has anyone experienced this? What do I check next? Do I pull the battery every night and hope things are great in the morning? Could it be those plugs and wires? Should I have done the rotor cap too? Does the computer have a gripe with the O2 sensor? Why arent' any warning lights coming on if that is the case? Please help. Thank you.

 

Bump...help.

 

Bump bump...help help. I havn't pulled the battery in more than a week, and things just seem to get worse. Trying to merge on the highway, the car just bucksand gasps if the RPMs are too low. How do I check the computer? Is is the oxygen sensor? Because I get such an improvement when the electrical system is reset, it seems like it has to be "smart" part of the car, not mechanics. Please help.

 

Well, I guess nobody is replying because your problem is really hard to troubleshoot. I don't have any idea what this is, either. If this was my car, at that point I would probably got another ECU from a junk yard and gave it a try. It shouldn't be more than 100 bucks.

 

Did you replace the air filter? I also think that its worth changing the cap and rotor on the distributor if you haven't changed it in a while. You can look at the computer's sensor inputs using a scan tool (not a code reader, you need a real scan tool). It could be possible that the ignition timing is not bieng advanced when you hit the gas which would explain the bogging down. This is the job of the PCM (engine's computer). Do you remember what the exact trouble code was when you the check engine light on?

 

Sounds pretty odd...I know this is going to sound stupid but have you been working on cars for a while or is this your first time? Has your car been regularly serviced based upon honda's recommendation (valve adjustments, timing belt, etc...)

It would have been smart to replace the all the spark components when you changed the plugs origonally (plugs, wires, coil, etc...) And there is a small chance that if your O2 sensor fouled out your spark plugs might not be in the best shape either (causing poor performance and mpg). If you plan on replacing the coils (if you haven't all ready done so) it would not hurt to pull each plug and check the condition of each and replace if they need it. Check and make sure your timing is correct as well.

Is there any gas leaking from where you changed the fuel filter, or was it done correctly?

This is pretty hard to diagnose, but it may give you something to work with. I hope this helps some...let us know if you find anything else out!

Good luck!

 

I havn't done much to this car. I've changed/checked all fluids and lubes on a regular basis. I put new front brake pads on, the rotors looked great. Last time I checked the rear drum pads they were still fine. At 95,000 I just put new tires on for the first time. Really, this car has been great...but perhaps I've missed something like you suggest since I'm still very much an amateur with cars. I put a new air filter in last night...it was overdue. If anything, the problem is worse. For example, while idling ata light the engine will hmmmmmmmmmm duh hmmmmmmmmmm duh hmmmmmm duh duh hmmmmmmmm etc. What would I notice if the spark plug gap was wrong on those new plugs I installed? What should the gap be if I get a feeler gauge? I suspect the O2 sensor was fouled by the injector cleaner. Again, the plugs are still quite new, but I'll check them as soon as I have a chance. Clearly the engine studders I notice only happen at low RPM or high engine load. The mileage is the other indicator of something amiss. Thanks for some ideas, please keep them coming.

 

You can try cleaning out the intake air control valve with some carb cleaner. Also, try running some seafoam through the engine (see the DIY section) and see if that helps.

 

Please excuse basic questions. I would remove the filter and spray carb cleaner into the air inlet? Would I do this with the engine running? The original code was for the O2 sensor, but this problem existed before that. Also, can sea foam foul the O2 sensor or anything nasty like that?

 

The problem may be solved...does this make sense? I checked the plug gap last night and all were perfect.When I went to pull the plugs, the engine was hot and I didn't need a wrench to loosen them. The book calls for 13 foot*lb which is pretty low and also says to remove plugs only when engine is cold. Now when I originally put them in I did this, but it is evident that plugs are loose at high temps. I forgot to mention that the original problem only happens once the engine is warmed up. Is it possible that I was occasionally loosing compression due to this? I put them back in at about 10 foot*lb with the engine still hot. Today there was not a single incident of engine catch for 22 miles to work.I hope it's not a coincidence like so many other times. I'll get back with the mileage later in the week. I'd still be interested in the cleaning steps mentioned in the above post if anyone has input.