I have a 2004 Honda Accord 4-Cylnder Coupe with 137,000 miles. My car has started vibrating violently at low RPMs and when idling. Tried replacing all engine mounts as they were in bad shape but that fixed nothing, in fact made it more noticable. Engine itself is running great. Transmission?
What makes you say that the engine is running great? Just because if “when idling” means when the car is at a standstill, and you’ve replaced all of the engine mounts, the stuff left is basically either a misfiring engine or incorrect new mounts or mount install.
Maybe you could describe “vibrating violently” better and the conditions along with what “engine running great” means to you.
The engine mounts are definitely the right ones and installed correctly. We did the procedure twice just to make sure. The engine is not misfiring as the vibration does not occur all the time and it’s not getting worse. Sometimes it does it when the car is idling (particularly when the air conditioner is on), and it is worst when the car is accelerating between 0-10MPH. Car feels perfect when running past 10MPH. Engine has passed inspection. Vibrating is like a loud, “Duh,duh,duh,duh,duh,duh…” and rattles everything.
The first thing I would do is run a compression test. One low cylinder can cause a vibrating engine that will smooth out when the RPMs rise.
While a 137k miles Accord engine should not have a mechanical fault (at least in theory) if the valve lash has been neglected and a low compression situation exists due to a tight valve then it’s quite possible for this problem to occur.
A cylinder head valve seat and valve won’t take very many miles of tight lash before they burn and once that happens it’s time for a complete, and expensive, valve job.
If the compression shows low then one should inspect the valve lash and adjust as necessary. Whether that’s closing the barn door after the horses escaped is unknown.
A vacuum leak could also cause this. (better this than a tight lash problem.)