Goofy honda idle logic?

[dobsont]

I've got an 02 CR-V, Manual 5spd.

It idles high when the engine is cold -- that's fine. That's high idle. it's usually somewhere between 1300 and 2000 rpm. Why it isn't consistent, I'm not sure. But that's not really the issue. Actually there's sort of two issues:

Let's say the engine is up to temperature. I make a 15 minute stop. Jump back in and drive - the temp gauge is still up but it still goes into high idle. This is really annoying for NICE-on coasting because its sitting there revving when it doesn't need to. After a couple of minutes it returns to its normal idle state -- about 800.

When it's really cold (like -30c) I've noticed it doing a weird repeated rev up from 1200 up to about 2500, back down to 1200, back up to 2500, again and again until the engine is good and warm. Again, it isn't consistent - some days it'll do it, some days it won't. That one has probably only happened a couple of times.

Sometimes I'm wondering if the throttle isn't sticking or something.

Anybody else notice weird stuff with Honda idle logic?

[msantos]

Originally Posted by dobsont

...

Anybody else notice weird stuff with Honda idle logic?

Yep. O2 sensors have been found to produce fluctuating signal levels especially in the winter months. Things get worse depending on the type/brand of gas used.

Cheers;

MSantos

[Maxx]

Be happy you don't have my issue - If I FAS and bump start the engine management goes into "idle mode" indefinately until I turn the car off at a stop (00 nissan altima).

[dobsont]

Phew - glad I'm not crazy then.

I was thinking to change my o2 sensors as part of spring cleanup. Do they get worse over time or are new ones just as prone to produce fluctuations? In any case, If they haven't been done its probably time.

Maxx - yeah, that'd suck! I kinda think mine actually DOESN'T go into idle mode after a FAS, only after I've been stopped a while. Can't recall if it does it after a FAS to a stop.

[shifty35]

It's not the "logic", it's the sensors and actuators.

The IACV and FITV (don't think the 02 CRV has a FITV, but older Hondas do) tend to get gummed up and clogged, leading to funky idles. Also air bubbles in the coolant can cause this.

[phoebeisis]

Maybe this is normal at the low temperatures you have in Canada.I would think that the catcon,intake manifold,FI system,fuel lines -all the tubes that are on the outside of the engine and car would cool down pretty quickly.The fuel in the tank is pretty cold where you are this time of year.
Does it do the same thing on your warmest summer days?
On the -30 days maybe the cold fuel is so poorly vaporized that you get a very poor burn-or maybe a miss-.The O2 sensor in the exhaust manifold will show lots of 02.The ECM would know that it had given lots of fuel,since the mass sensor would have told it how much air-and O2(20%)-was there.It would then know that it needed more REVs to warm everything-all the tubes with fuel,air and mixture-and the cat con- up more quickly.Maybe the ECM has instructions for cold climates to cover this-something like,"idle to 2500 for 15 seconds then drop to 1200-see if this helps-repeat until the right amount of O2 is sensed."I wonder if these vehicles have a "cold weather miss sensor"-if missing is detected then idle up-repeat.
Charlie
PS-Or maybe something is just sticking or gummed up.Has it always done this?If this is new,then obviously something is "bad". If it has always done it, it probably is ok-and just Honda's logic.

[invaliddata]

Something is wrong with your car. Usually surging idle occurs with warm engines and is the result of: 1) bad iac valve 2) misadjusted throttle, 3) a leak in the intake system.
What is going on is the fuel cut programming that's responsible for DFCO. All these problems lead to excess air, which is detected by the MAP sensor and the computer supplies fuel to compensate. However, if the throttle is also closed, as measured by the throttle position sensor, the computer shuts off fuel above a certain rpm level. But since the leak that caused the rpms to go so high is still there, the process repeats.

I'm almost 100% certain that surging idle isn't an o2 sensor problem (although the high initial idle may be). The reason why is if the sensor is constantly rich, the computer will detect this as an abnormal condition and throw a code. There is a limit to how much the o2 sensor can be used to adjust the base fuel map (about 30% in my car), and this will also throw a code (and light the MIL). Most sensors have some basic rationality parameters like this, so if the inputs are totally wacky (like if you've disconnected something), the car will tell you right away.

What you should do is check the live sensor data for things like the MAP, IAT, TPS, coolant temp, etc, and see if things make sense.

Besides the surging idle, the consistent high idle may be a normal thing. Compare with other similar cars. Some cars do that to help warm the engine faster or for the cats or the o2 sensors (could be an older, marginal 02 sensor causing this). My car idles high regardless in response to road speed, even in neutral.

[dobsont]

We've had the CR-V since December, so I have no idea what it does in warm weather. It has done the idle surge thing exactly twice -- both on incredibly cold days. When its only -20C, say, there's no problem.

The high idle is probably more or less normal -- it just likes to idle high for the first few minutes after it starts -- no doubt related to warmup. The fact that it does it when the engine is infact already warm would likely be missed by most people, since (and I'm assuming here) most people aren't doing a lot of NICE-on coasting.

We'll see how the dfco circuitry is working when my scanguage arrives (hopefully this week). No maintenance lamps are lit, so I assume there are no error codes. Again, we'll see.

Thanks for the input! I'll post back when I know more.