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Poor gas mileage connected to idle learn procedure

99K views 124 replies 56 participants last post by  honda2011 
#1 · (Edited)
I just thought I'd post this in regards to some people complaining of poor gas mileage. It may have been discussed here before, but I've read alot of the mpg threads and don't recall mention of it. This has been talked about alot on the net recently in regards to the Honda Fit, but these Fit users learned it from a Honda Pilot Forum which brings us to the Ridgeline since it shares the same engine as the Pilot.

Pilot users were complaining of poor mpg, and after performing the "idle learn procedure" they gained like 5 to 7 mpg.

Idle learn procedure from my memory is:

(make sure AC/heat and other accessories or off before step one)

1- disconnect neg batter cable for 5 minutes
2- reconnect neg battery cable
3-start vehicle
4- Let the vehicle idle through two fan cycles, and after the fan shuts down after the second cycle, let it idle for 10 more minutes
5-shut off vehicle and start it back up and punch in your radio code.
 
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#2 ·
You may only be able to do this with the aid of the Honda Diagnostic System, ie during a trip to the dealer, but the official Idle Learn Procedure is as follows (verbatim from page 11-266 in the Service Manual):

1. Make sure that all electrical items (A/C, audio, lights, etc) are off.
2. Reset the PCM with the HDS (see above)
3. Turn the ignition switch ON (II) and wait 2 seconds.
4. Start the engine. Hold the engine speed at 3,000rpm without load (in Park or Neutral) until the radiator fan comes on, or until the engine coolant temperature reaches 194F (90C).
5. Let the engine idle for about 5 minutes with the throttle fully closed.

Note: If the radiator fan comes on, so not include it's running time in the 5 minutes.
 
#5 ·
Lingered_I said:
You may only be able to do this with the aid of the Honda Diagnostic System, ie during a trip to the dealer, but the official Idle Learn Procedure is as follows (verbatim from page 11-266 in the Service Manual):

1. Make sure that all electrical items (A/C, audio, lights, etc) are off.
2. Reset the PCM with the HDS (see above)
3. Turn the ignition switch ON (II) and wait 2 seconds.
4. Start the engine. Hold the engine speed at 3,000rpm without load (in Park or Neutral) until the radiator fan comes on, or until the engine coolant temperature reaches 194F (90C).
5. Let the engine idle for about 5 minutes with the throttle fully closed.

Note: If the radiator fan comes on, so not include it's running time in the 5 minutes.
From what I gather in my reading, disconnecting the negative batter cable from the battery will accomplish step 2 Reset the PCM with the HDS so the HDS (Honda diagnostic system) won't be needed.
 
#6 ·
If this/these are the definitive methods of finessing the "learn idle", how long will it take for me to clumsily "reteach my idle" my bad habits? :rolleyes:
I mean... is this procedure going to have a lasting effect on an otherwise smoothly-running system? And how would you know if you actually NEEDED to perform "the procedure"? A reading of rpm @ idle? (I think mine's around 6-700)

Anybody have an explanation as to what this accomplishes and/or how it could go overlooked in the PDI?

I supppose idle does have something to do with gas mileage, and I'd think that some of this involves tricking the puter into delivering a "less rich" mix to the plugs. I'm no engine mechanic (as you can probably tell :rolleyes: ), but wouldn't this, then also, involve a timing adjustment?

Alotta questions... I've seen the Pilot owners' comments, but haven't seen if the Fit owners' have found an explanation for the correlation between it (ILP), and MPG.

Thanks Ridge, for the thought-provoking post. :cool: Any links to further discussions would be welcome.
 
#7 ·
This procedure would give the Ridgeline an extra 5 or 6 miles per gallon? That is huge! If this were true I would expect Honda to let us know and call us in to the dealer to have the thing set up right. That mileage increase is something like 20% and that is almost unheard of by a "minor" idle adjustment. If this procedure works (and with no long term ill efffects) it means there was a major blunder made at the assembly plant and Honda should correct it.
 
#9 ·
Pug said:
A reading of rpm @ idle? (I think mine's around 6-700)
If the idle learn procedure was off would the error show on the Tach? If so, what is the correct idle speed setting? Isn't this part of the get ready procedure performed by the dealer? It's listed in my Honda Service History Booklet and was checked off by my dealer as being done by them. Hopefully correctly.

Most of my driving is short trips, less than 2 miles at a time, my gas mileage is around 14.5 with A/C running all the time. On the road, which is done rarely, I've gotten 21.3 mpg. I think my numbers are respectable. So I assume the idle procedure was done and done correctly. Any feelings on this?
 
#10 · (Edited)
Ridge said:
From what I gather in my reading, disconnecting the negative batter cable from the battery will accomplish step 2 Reset the PCM with the HDS so the HDS (Honda diagnostic system) won't be needed.
I'm not so sure about that because there are dozens of reasons for disconnecting the battery, and it would be surprising to find that the PCM is reset so easily.

The service manual states that the idle procedure be run whenever you replace, reset or update the PCM, or replace/clean the throttle body. No mention of just disconnecting the battery. In sections of the manual that require the battery be disconnected, there is mention of re-entering the radio codes, and re-arming the auto window, but nothing else.

The procedure for diagnosing the idle on your truck, to see if needs to be reset, is as follows:

1. Disconnect the EVAP canister purge valve connector.
2. Connect the HDS (this can probably be skipped)
3. Start the engine and hold the revs at 3000 in Park or Neutral until the radiator fan comes on, then let it idle.
4. Check the idle speed without any load: headlights, blower fan, radiator fan and air conditioner off. It should be 730+/-50.
5. Let the engine idle for 1 minute with high electric load: headlights on main beam, AC set to max cool, blower fan on high. It should still be 730+/-50.
6. Reconnect the EVAP connector.

If the rpm's were out of scope, the learn procedure should be performed.
 
#11 ·
jsant01 said:
If the idle learn procedure was off would the error show on the Tach? If so, what is the correct idle speed setting? Isn't this part of the get ready procedure performed by the dealer? It's listed in my Honda Service History Booklet and was checked off by my dealer as being done by them. Hopefully correctly.

Most of my driving is short trips, less than 2 miles at a time, my gas mileage is around 14.5 with A/C running all the time. On the road, which is done rarely, I've gotten 21.3 mpg. I think my numbers are respectable. So I assume the idle procedure was done and done correctly. Any feelings on this?
There is also the TP Position Check which has to be performed to calibrate the Throttle Body. Mine is at 14% open when idling, which I think has been comfirmed by other members who have a ScanGauge or similar. That check is performed before the Idle Learn procedure and corrected if necessary. Then the Idle Learn procedure is performed after which, the Crankshaft Pulley (CKP) pattern learn procedure has to be performed. All 3 procedures are required if the PCM gets replaced - not sure if all 3 are listed on the Dealer checklist.
 
#12 ·
Pug said:
If this/these are the definitive methods of finessing the "learn idle", how long will it take for me to clumsily "reteach my idle" my bad habits? :rolleyes:
I mean... is this procedure going to have a lasting effect on an otherwise smoothly-running system? And how would you know if you actually NEEDED to perform "the procedure"? A reading of rpm @ idle? (I think mine's around 6-700)

Anybody have an explanation as to what this accomplishes and/or how it could go overlooked in the PDI?

I supppose idle does have something to do with gas mileage, and I'd think that some of this involves tricking the puter into delivering a "less rich" mix to the plugs. I'm no engine mechanic (as you can probably tell :rolleyes: ), but wouldn't this, then also, involve a timing adjustment?

Alotta questions... I've seen the Pilot owners' comments, but haven't seen if the Fit owners' have found an explanation for the correlation between it (ILP), and MPG.

Thanks Ridge, for the thought-provoking post. :cool: Any links to further discussions would be welcome.
I own a Fit, and the idle learn procedure (ILP) has been discussed quite a bit on Edmunds.com and Fitfreak.com Some people that were dissappointed with their Fit mpg performed the ILP after hearing about the Pilot owners, and went from like around 27 mpg to in the 31-33 mpg neighborhood. I don't know, I'm not a mechanic. I just thought I'd throw it out there since the pilot and the Ridgeline are basically the same.
 
#13 · (Edited)
Lingered_I said:
I'm not so sure about that because there are dozens of reasons for disconnecting the battery, and it would be surprising to find that the PCM is reset so easily.

The service manual states that the idle procedure be run whenever you replace, reset or update the PCM, or replace/clean the throttle body. No mention of just disconnecting the battery. In sections of the manual that require the battery be disconnected, there is mention of re-entering the radio codes, and re-arming the auto window, but nothing else.

The procedure for diagnosing the idle on your truck, to see if needs to be reset, is as follows:

1. Disconnect the EVAP canister purge valve connector.
2. Connect the HDS (this can probably be skipped)
3. Start the engine and hold the revs at 3000 in Park or Neutral until the radiator fan comes on, then let it idle.
4. Check the idle speed without any load: headlights, blower fan, radiator fan and air conditioner off. It should be 730+/-50.
5. Let the engine idle for 1 minute with high electric load: headlights on main beam, AC set to max cool, blower fan on high. It should still be 730+/-50.
6. Reconnect the EVAP connector.

If the rpm's were out of scope, the learn procedure should be performed.

I don't know, I'm not a mechanic. I don't even play one on TV:D, but the Fit/pilot people just disconnected the negative battery cable and it seem to work for them. I haven't tried it yet with my Fit. I'm waiting for more Fit owners to report in about it. I'm getting around 27/28 mpg with city driving for the Fit currently. If the ILP will help it close in on the 33 mpg the EPA says it should get, I might give it a try.
 
#14 ·
shortspark said:
This procedure would give the Ridgeline an extra 5 or 6 miles per gallon? That is huge! If this were true I would expect Honda to let us know and call us in to the dealer to have the thing set up right. That mileage increase is something like 20% and that is almost unheard of by a "minor" idle adjustment. If this procedure works (and with no long term ill efffects) it means there was a major blunder made at the assembly plant and Honda should correct it.
I don't think it's a blunder at the plant, but maybe some Ridgelines were set up improperly at the dealer in regards to the idle learn procedure. It seems like I've heard some people complain of getting 14mpg in the city. Maybe ILP can get them to the 18mpg nieghborhood where they belong.
 
#15 ·
Ridge said:
I don't think it's a blunder at the plant, but maybe some Ridgelines were set up improperly at the dealer in regards to the idle learn procedure. It seems like I've heard some people complain of getting 14mpg in the city. Maybe ILP can get them to the 18mpg nieghborhood where they belong.
I wonder why this procedure is done initially at the dealership and not at the factory. Is it because atmospheric conditions come into play, requiring that it be done in the area where the truck will be used most often? Is it done at the factory and then the setting is lost due to the battery being disconnected during shipment? Is it left to the dealers simply to keep production costs lower?
 
#16 ·
ridged said:
I wonder why this procedure is done initially at the dealership and not at the factory. Is it because atmospheric conditions come into play, requiring that it be done in the area where the truck will be used most often? Is it done at the factory and then the setting is lost due to the battery being disconnected during shipment? Is it left to the dealers simply to keep production costs lower?
What you say makes sense. Your probably right.
 
#19 ·
Ridge said:
I don't think it's a blunder at the plant, but maybe some Ridgelines were set up improperly at the dealer in regards to the idle learn procedure. It seems like I've heard some people complain of getting 14mpg in the city. Maybe ILP can get them to the 18mpg nieghborhood where they belong.
Just as some were sold with 45psi in the tires.;)
 
#20 ·
One explanation of the Idle Learn Procedure is here.
**Please Note - This is NOT the HONDA idle learn procedure. It's for GM vehicles. I'm just providing the link for reference and a better understanding of what's going on with an engine. Click the embedded link there for info about the idle air motor, too.
 
#21 ·
arteegee said:
True, I disconnected mine for the hitch/harness install. But then I didn't do the other steps.
The plot thickens.

Look at step 50 in these instructions for fitting the hitch to the 2006 Pilot, which involves disconnecting the battery.

http://www.handaaccessories.com/pilot/06hitch.pdf

Now the instructions for the Ridgeline:

http://www.handaaccessories.com/ridgeline/hitch.pdf

No mention of the PCM or Idle Learn Procedure.
Is that an oversight, or does disconnecting the battery in the Ridgeline really not reset the PCM? I have scoured the Service Manual, and every operation that involves disconnecting the battery, does not mention the Idle Learn, yet they all mention the auto window and radio codes. I'm thinking that the PCM settings are preserved on our truck.
 
#24 ·
Katin said:
As much as I wanted to belive it guys...Looks like the damn dealer is the only one that can do it...but will they? NO! Ralph Schomp in Littleton Co told me there is no way to reset anything, Unless a check engine light comes on there is no problem.

This was found on Drive Accord. Princess has an inside track.

http://www.driveaccord.net/forums/showthread.php?t=6657&highlight=idle+learn
Yikes! :eek: Something I'd never attempt... looks like too much other stuff involved...

From the service pdf provided in the above link:

If you try to clear DTCs on a Honda vehicle using the HDS or PGM Tester in Generic OBD II mode or a generic scan tool, you might not get the results you’d expect. That’s because Honda vehicles actually use three different kinds of clear commands: DTC CLEAR, ECM/PCM RESET, and more recently, CKP PATTERN CLEAR. If you’re using the HDS or PGM Tester in Honda System mode, the level of clearance varies. If you’re using the HDS or PGM Tester in Generic OBD II mode or a generic scan tool, there’s just one clear command.
It clears all learned values.
And furthermore:

Since all the learned values are cleared in Generic OBD II mode or with a generic scan tool, don’t forget to do the idle learn procedure. And if you’re working on a V6 model, don’t forget to do the CKP pattern learn procedure, or you could wind up with a misfire DTC when there’s really no problem. Refer to the appropriate S/M or ISIS for idle learn and CKP pattern learn procedures. If you’re working on a ’05 Accord Hybrid, you need to be really careful here. Always turn the ignition switch to LOCK (0) after clearing the DTCs. If you don’t, and you start the engine right after clearing, you could damage the IMA battery.
Thanks for the link, Katin.
Pug



"* This command is available only on the HDS." (refer to attached pic)
 

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#25 ·
I oftened wondered about altitude change and idling. I know older cars used to have to have the altitude adjusted. I am constantly at 3300-4500 (above sea level) where I live/work.

Next time in I will ask my service dealer about it. I am getting satisfactory mileage ( average is 17.5-18.5 mpg) so I don't know if I would do a lot better.

Thanks for all the insight. This has been a useful thread and interesting thread :D
 
#26 ·
I think that the bottom line for this whole thread is that your warm engine idle revs should be 730 +/-50 under all electrical load conditions while in Park or Neutral. If it isn't, take a trip to the dealer to get the Idle Learn procedure performed. Trying to trick the PCM into a fault, then a reset in order to do it yourself is too much trouble.
 
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