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2008 2.4L Auto low idle warm in gear only

12288 Views 20 Replies 7 Participants Last post by  CesarEstrella
Hi, I have lurked on this forum for the past couple years since I bought my accord but now have question to ask.
I have a 2008 Accord EX-L 2.4L Auto 80k miles
Car runs great except when fully warmed up in gear at a stoplight with foot on the brakes. At this time the idle will dip down to about 500-600 and there will be a slight vibration felt in the cabin. When cold there are no vibrations and the idle is smooth. rough idle is present with AC on or off. I peeked at the engine mounts and I dont see any cracks. Air filter only has a few thousand on it. I put a bottle of techron in a couple tanks ago with premium gas but no change. I always buy top tier fuel. I have checked the PCV per the service manual and I get a nice click when hose is pinched. No CEL or MIL. ATF drain and fill has been changed at 30k x2, 60k x1,
So what I'm thinking is one of 2 things.
1. EGR if the car has one. all of my searching pulls up older cars and cleaning idle air circuits. If EGR is functioning when car is hot and is clogged this would seem to make sense. Part search reveals a EGR gasket but no valve...? seems the V6 has a part to clean but not the 4cyl.
2. Valve adjustment? if this needed to be done would I only see the effects at idle in gear but not out of gear? I doubt it.
Thanks in advance.
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I would clean the IAC and the Throttle Body, as well as doing a valve adjustment. Be sure to check for a vacuum leak as well, may be a cracked hose or intake gasket that does not open up until the temperature rises.

The EGR vlave is not in use at idle.
I would clean the IAC and the Throttle Body, as well as doing a valve adjustment. Be sure to check for a vacuum leak as well, may be a cracked hose or intake gasket that does not open up until the temperature rises.
Car has an electronic throttle body(ill check it out) and I don't believe it has an IAC like pre 2008 honda's
You are correct, the 2008 has an electronic throttle, no IAC. I would still remove the throttle body and clean it carefully, do not spray cleaner directly into the throttle body on the car, remove the Throttle body and spray cleaner on a clean rag and wipe the throttle body clean of carbon. Then I would clear the ECM and do a Idle relearn procedure.

1. Turn the key on
2. Wait 2 seconds
3. Start engine and run at 3,000 RPM until the cooling fans come on
4. Let engine idle for 5 minutes with no load

I would still do a valve adjustment.
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I pulled the big hose from the airbox to the throttle body off and looked at the throttle body, it looked like this...

Then I turned the key to ON, without starting the car, and put a brick on the accelerator. This opened the throttle body.
I sprayed some throttle body cleaner on a rag and wiped everything I could reach. Then it looked like this.

and idled like this

this is what came off on the rag, not really that much gunk...

I didnt disconnect anything so I didnt reset anything. Seems better at least for now. After putting it back together I checked the PCV just for fun, tiny bit of oil residue on the inside end of it but working well. Sprayed some carb cleaner in it and put it back together.
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Any update on your car? Did cleaning the TB solve your issue. I am having the same problem on my 2010 EX 2.4 w/ 37,000 miles.

My car idles around 700-750 when its warmed up and in gear... thought it was normal since its getting warmer out. In the winter it'd idle around 1000-1100. Should I look into getting my car checked out too?
105k miles and it still does it. It is either normal..... Or... I really think the front vacuum assisted mount is bad, when I check it using a vacuum gauge the.idle doesn't change
bryb086- Thanks for the reply. I just had my car at the dealer all day yesterday. I took with me the TSB 04-024, which although for the 7th gen describes my issue. They went ahead and replaced the front mount and loosened, sat (P-R-D) and torqued the rest of the mounts. And... nothing the vibrating is still there. My RPM drops to 650 when in D and the car is at driving temp. Dealer suggested a valve adjustment but could not guarantee it would take care of the issue. I'm with you and just going to cal it a Honda idiosyncrasy.
A 4cyl engine at low idle isn't going to be totally smooth. Although to me the vibration isn't really that bad in the cabin.

The 8G I4 doesn't have EGR. The engine uses intake / exhaust valve timing to deal with that.
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It seems that when it drops to the 650 range the vibration begins. Is the RPM drop when in D, from 800RPM in P or N to 650 in R or D normal? I am aware thatt he 2.4 isnt smooth at idle, sitting waiting for my car at the dealer all the 2.4's coming in were idling noisy I can deal with that, its the vibrating that concerns me. But I can also live with it if its normal to the 2.4 which it is starting to look that way. Thanks All!
Yes 650 rpm in D is normal. If you turn on your headlights or the blower fan then the rpm will rise to compensate for the extra engine load.
Thanks drowned12. Reading the various forums this seems to be a 2.4l signature across various models. I guess I can rest at ease but still not exactly thrilled that Honda is Okay with this.
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I personally adjusted my valves and put in new spark [email protected] miles.
While this did get me 1-2 mpg... and restored car to stock MPG's it didn't change the low/rough idle in gear when warm.

Im curious rluna did the dealer use a vacuum gauge to check the front mount?

When I showed the tech the vacuum gauge and procedure for testing in the service manual he seemed confused?

See here 2008 Accord I4 low idle/vibration help | Mechanical /Maintenance Forum | Bob Is The Oil Guy
brybo86- I am not sure if they checked. I showed the adviser the TSB 04-024 and said this seems to be a know issue with Honda. Hours later she called and said the front mount was bad and it will be replaced. I am within a month of my powertrain warranty running out so perhaps they did jump in on an opportunity for work.
I wrote a letter to Honda corporate this week asking for an extension to my power train warranty so we'll see what happens.

Just to confirm with your experience, for you was this an issue tha always existed or did it develop? Mine began about 5,000 miles/6 months ago so I know something has changed.
I think it developed at about 70k miles?
Have you also checked your alternator and battery?
08EX-L I have not thought about the alternator and battery but I think you might be on to something. Ill look into it. Another possibility is the trans. Once I am able to upload images and PDF's ill share what I found in the service manual, which i think might help.
when the issue started i had autozone test the batt and alternator.
But i haven't had any issues starting even with the tiny battery...?
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