Hi,
I did find a post with exactly the same issue from July from someone else but it was never resolved

My 2006 4cyl has a problem I can't pin point.
The car idles very rough when the car is in gear, AC is on and the radiator fans are running. It smooths out a little when the fans stop w/ AC still on and completely smooths out when the AC is off.
It also will idle smoothly if I put the car in neutral.
It idles fine without the AC on.


This problem started a few years ago and slowly has gotten worse to the point that I come to a stop light and automatically throw the car into neutral to avoid the car shaking.

Nothing to do with this issue, but I just replaced timing chain and purchased a complete rebuilt head including cams. I kind of hoped that this would have helped...

Anyone have any ideas?

Thank you
Mark

 

A weak COP unit might miss under load. Are spark plugs reasonably fresh?

Any Check Engine Light? If yes, get codes and check for P0300 or other miss codes.

good luck

 

Thank you for the response....
I have searched the Internet and this seems to be a fairly common issue? But haven't found the fix. Could this be an issue with the AC system itself? I saw a few posts suggesting that as a possible issue. If pressure were too high would it cause this? I had the AC seviced a couple years ago by a shop.

There are no codes / check engine light.
The spark plugs were replaced 6-8 months ago.
What is COP unit? Coil pack? Car seems to run fine under hard acceleration. But I have never changed them.

 

COP = Coil on plug

I'd look at cleaning the TB - pretty sure the 06 is DBW -drive by wire - so there isn't a good way of getting to the back side of the throttle body butterfly besides pulling the TB from the plenum. If you are ok with doing a bit more you could pull the plenum as well and give it a good cleaning.

Another thing to look at/think about. Be sure there are not any "tears" in the intake tube from the air cleaner to the TB. Next is cleaning the mass air flow sensor.

Cost, your time, a throttle body gasket, plenum gasket (it is metal and could be a re-use item ) and a few cans of carb cleaner and one can of mass airflow cleaner.

 

Thank you. I will definitely do those things.
I will clean the TB, mass sensor and check for leaks..
Since I just had the head off, I cleaned the intake with carb cleaner and replaced both gaskets.

Mark

 

Although it ends at the 2004 MY 4 cylinder, I have no reason to believe there would be any difference through the 2007 MY.

Google Honda service bulletin 04-024.

"Engine vibrates while idling in gear"

 

The TBS does sound like exactly what is happening. And would make sense for this car since engine is the same as year in TBS.
I know the mounts are good. I just replaced the rear and the transmission mounts. I had both the front and passenger side mount out of the car and they looked ok. No tears etc.

All of them are aftermarket mounts since I had to replace them before. Do you think that could be an issue?

 

Could be, most things on these newer cars require OEM parts...if you don't want to do it twice.