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Discussion Starter · #1 ·
I have a 2008 Honda Ridgeline RTL with only 75k. Have not done anything to it beyond regular oil changes. Suddenly this rough idle started. Only when in gear. The idle is a little fast too. It is obvious when braking/slowing to stop, the truck surges a bit when it makes the last downshift into 1st, right before the truck comes to a complete stop. While at a stop sometimes it would idle so rough the shift lever would be vibrating so bad it was almost blurry. However put it in park and she purrs. No vibration. Only in drive. No CEL or codes displayed.

On a hunch I disconnected the battery for about an hour. After reconnecting the battery the problem was solved... or so I thought. The truck purred like a kitten, and ran perfectly for about 2 or 3 weeks. (Not much driving, about 15 miles a day plus an extra 100 miles or so total over a weekend or 2.) Suddenly the problem came back.

Any ideas what the problem might be? I have combed the web but can't find anything like this issue. Thanks!
 

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I have a 2008 Honda Ridgeline RTL with only 75k. Have not done anything to it beyond regular oil changes. Suddenly this rough idle started. Only when in gear. The idle is a little fast too. It is obvious when braking/slowing to stop, the truck surges a bit when it makes the last downshift into 1st, right before the truck comes to a complete stop. While at a stop sometimes it would idle so rough the shift lever would be vibrating so bad it was almost blurry. However put it in park and she purrs. No vibration. Only in drive. No CEL or codes displayed.

On a hunch I disconnected the battery for about an hour. After reconnecting the battery the problem was solved... or so I thought. The truck purred like a kitten, and ran perfectly for about 2 or 3 weeks. (Not much driving, about 15 miles a day plus an extra 100 miles or so total over a weekend or 2.) Suddenly the problem came back.

Any ideas what the problem might be? I have combed the web but can't find anything like this issue. Thanks!

Sounds as if your IAC (idle air control) valve could be going out. You can try cleaning it as well as your throttle body. There is also a procedure to reset base idle, which you can find on this forum by searching. I haven't seen it in a couple years, but I know it exists. Are you sure that you don't have a cylinder misfiring? I know you said you had no codes, but a misfiring cylinder would cause the rough idle you are feeling as well as the idle being high because the PCM will try to compensate for the lost cylinder.
 

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Discussion Starter · #3 ·
I suppose the IAC could be going out. Or is dirty or sending inaccurate info to the ecu.

But bad cylinders wouldn't explain how disconnecting the battery fixed it, temporarily.

Also, when I shift it from the most roughest idle (while in drive) say at a stop light, into park, the engine purrs. And I mean purrs. Shift it back into drive and it's rough again.
 

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2008 Ridgeline RTS in Billet Silver Metallic
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Check your spark plugs/coils for overall condition and make sure the plugs are properly torqued (13 lb-ft). Just eliminate the possibility of a loose plug with the associated problems that entails.

I would check for any codes too, just in case the CEL isn't showing for some reason.
 

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Discussion Starter · #8 ·
I will check them this weekend, just for good measure. As well as check for any codes. However, today at a long stop light it was idling bad and I shifted into neutral and she just purrs. Shift back into drive and she purrs for about 1 to 1.5 seconds and then there is this hiccup and then starts running rough again. The hiccup is hard to describe but its like it misfires once and then runs rough there after. The hiccup is like that jolt when a AC compressor engages, only more aggressive.

Keep in mind, I switched back to neutral and she purrs again. Back into drive and the hiccup reoccurs along with the rough idle. WTH?!?! :act060:
 

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I will check them this weekend, just for good measure. As well as check for any codes. However, today at a long stop light it was idling bad and I shifted into neutral and she just purrs. Shift back into drive and she purrs for about 1 to 1.5 seconds and then there is this hiccup and then starts running rough again. The hiccup is hard to describe but its like it misfires once and then runs rough there after. The hiccup is like that jolt when a AC compressor engages, only more aggressive.

Keep in mind, I switched back to neutral and she purrs again. Back into drive and the hiccup reoccurs along with the rough idle. WTH?!?! :act060:
Could be a bad motor mount/transmission mount.

What you are interpreting to be a misfire "rough idle", may just be the jarring caused by a bad mount.

Just a thought. :act002:
 

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Discussion Starter · #12 ·
The battery is about 1 year old.

Another interesting thing I discovered today, when it is running rough/fast idle while stopped (in Drive) in a parking lot, if I put it in Neutral it purrs (we know that) but I put it in Reverse this morning and noticed it purred in Reverse. Makes no sense to me what so ever. I can't really tell the RPM by looking at the gauge, but looking at the shift lever you can see it vibrating when in Drive, switch to Neutral or Reverse it stops vibrating. So weird. I will check for codes tomorrow.
 

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2008 Ridgeline RTS in Billet Silver Metallic
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It would be great if you lived near some ROCers who might be able to take a look. You don't post your location in your profile. That might be an option.
 

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The battery is about 1 year old.

Another interesting thing I discovered today, when it is running rough/fast idle while stopped (in Drive) in a parking lot, if I put it in Neutral it purrs (we know that) but I put it in Reverse this morning and noticed it purred in Reverse. Makes no sense to me what so ever. I can't really tell the RPM by looking at the gauge, but looking at the shift lever you can see it vibrating when in Drive, switch to Neutral or Reverse it stops vibrating. So weird. I will check for codes tomorrow.
That's GOT to be motor mounts.... ???
 

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Discussion Starter · #18 ·
I checked and didn't get any codes. Of course I only have a basic Craftsman code reader I bought about 4 or 5 years ago. It has always worked.

I noticed yesterday that the rough idle doesn't start when it's cold. It seems to start after it is warmed up. And you can't miss when it changes. There is that hicup where the engine sounds like it stalls for half a second and then the engine idle is rough. It happened to me while waiting at a red light. I wonder if it could be a vacuum leak that occurs when it gets to the right temp? Doesn't explain how it went away last time but I am grasping at straws before having to go to the stealership. Can't take it in just yet anyway because my F150 is in the shop. Wife and I are car pooling. Yea what fun. haha
 

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2008 Ridgeline RTS in Billet Silver Metallic
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I've seen electrical issues related to temperature before. But that wouldn't explain the reset fixing it temporarily or the part about it happening only in gear.

When you say it idles a bit fast, how fast exactly is the idle?







 

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I checked and didn't get any codes. Of course I only have a basic Craftsman code reader I bought about 4 or 5 years ago. It has always worked.

I noticed yesterday that the rough idle doesn't start when it's cold. It seems to start after it is warmed up. And you can't miss when it changes. There is that hicup where the engine sounds like it stalls for half a second and then the engine idle is rough. It happened to me while waiting at a red light. I wonder if it could be a vacuum leak that occurs when it gets to the right temp? Doesn't explain how it went away last time but I am grasping at straws before having to go to the stealership. Can't take it in just yet anyway because my F150 is in the shop. Wife and I are car pooling. Yea what fun. haha
It is probably time to take it in to a pro; at least for the diagnosis.

Perhaps you have bad motor mount(s) and some sort of other mechanical / electrical issue combining. The engine runs somewhat rough as a result of its own issue(s) but is felt only in drive due to mount issues???
 
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