Hey all,

I have looked throughout the forum and if someone has had this same issue, I'm not finding it.

I drive a 2002 Civic GX which runs on natural gas and has a CVT transmission.

Over the past year I've had a rough tremble in the engine bay when at a stop while in gear. It's only ever been a slight nuisance (especially while at the drive through window.) However, if I put the vehicle in park or neutral the tremble goes away.

Unfortunately, the problem has progressed. I first noticed that a similar little hesitation would happen when accelerating between 0 and 15 MPH almost like a little cough before engaging normally.

This last week, this hesitation has become increasingly consistent. Additionally, when I come to a stop and stay in gear, the idle sputters and some of the time the engine dies completely. However, if I shift to neutral when coming to a stop the idle stays consistent and doesn't drop.

I replaced the spark plugs today with NGK Iridium.

Other factors to consider:
- I have in the past had intermittent cylinder 3 misfires but couldn't get the code consistently enough to trouble shoot well and it hasn't given me that code for around a year.
- No codes are present on the ECM right now according to my OBDII reader
- I've considered the Ignition Coils (which are Denso and appear to be in good condition from visual inspection)
- Maybe needs a valve adjustment? Mileage is around 95k and I've had it since it was around 70k
- Could this be the timing belt getting sloppy? I know I probably need to do this soon anyway.

I'm off to clean the throttle body in hopes that helps. But I thought you all with experience might have some ideas on what is most likely to be the problem. I hesitate to replace the coils since I would think I would have more issues as well at high RPMs, freeway cruising, etc. . . but I literally ONLY get these sputters at low speed acceleration and when coming to a stop in gear.

Thanks in advance!

 

The clean may have helped, only had time for a quick test drive, but it still bogs down HARD when I come to a stop. Again this is only in gear. It almost feels like the idle dips as you're braking.

The IACV had quite a lot of gunk in it, but I couldn't get the star screws on the actual sensor to come off (they're a strange star instead of torx, allen, phillips, or flathead.) But I cleaned it out as much as I could and got a LOT of black deposits out.

Open to your thoughts!

Thanks

 

That may come from the crankcase breather, so check your PCV valve. If the valve allows too much crankcase pressure, the flow reverses through the breather that connects upstream of the TB, putting oily air into the TB. Keep trying to clean it until it doesn't give up any more gunk.

I don't remember strange fasteners on cars that I've owned, but Google for "security bits" & maybe you can find a tool for those screws. A set of those bits is handy for a lot of things that "consumers" aren't supposed to be able to fix.

 

Thanks JimBlake. You're a legend around here.

I'm sure you're right that the IACV screws were just specific safety screw, but what I meant by strange is that I didn't have the 5 pointed star driver to dissemble them.

I've been driving it for a few weeks since cleaning the throttle body. Still hasn't fully died on me at a stop, but it's come close.

I'll look at the PCV valve. I identified where it was when I was poking around in there for the throttle body, but I didn't pull it out. So you're saying I just need to clean it, right? I'll pull it off if I can find a few minutes today and clean 'er up.

Thanks for the input!

 

PCV valves are pretty simple. There's a plunger inside, on a spring. It should rattle when you shake it, and not be stuck in gooey crud. Its usually possible to clean out the crud, but I'm sure it's possible for it to be broken. Cleaning is the first step and it's not a lot of wasted effort if that doesn't work.

 

Well now that my busy season is over, i finally cleaned up my PCV valve. It was a bit oily, but didn't seem stuck.

I also drained and replaced the high pressure coalescent fuel filter which seems to have helped some. Honda Civic GX Coalescent Filters Change Procedure 2001 - 2005 Post 1 of 2 - Natural Gas Vehicle Owner Community

My idle seems stronger, but I'm still getting some lurching when i accelerate .

I'm now worried that might be the CVT transmission skipping I'm not certain how to troubleshoot that.The level of transmission fluid seems good on the dip stick!

Thanks for your help so far. Hopefully the coalescent diy is helpful to other GX owners with idle problems. Any other thoughts on the lurching would be awesome!

 

What live data can your OBD2 scanner read? Also look for any pending codes as well.

I'd look at fuel trims and misfire counter if they are available to start the diagnosis.

 

I really don't know anything specific about NG-fuel cars, but here's a couple random questions for you to look at (maybe something to search for in the NG-vehicle forums). I haven't seen hardly any questions here about NG-cars.

- There must be some kind of pressure regulator on the NG supply. How can they be tested? What's the supply pressure supposed to be? That would correspond to measuring the fuel pressure in a gasoline engine.

- In my work, I've seen a lot of analysis of pipeline natural gas composition. There's more variation than most people expect. Gas companies routinely dilute it with N2 or even air, to give a relatively constant LHV (energy content) despite variations from the amount of heavier hydrocarbons. That's good for a furnace or stove, but it's not good at all for some real technical users. And who knows what it does for an engine? So... What do people in the NG-car community say about batches of "bad fuel"?