I have a 98 Accord DX 4 cyl automatic. It has ~180,000 miles on it. This car had belonged to my son who passed away in 2011 and I am trying to keep it running for sentimental reasons. In the last 5 years it has had the break lines, the radiator, the timing belt and water pump, 2 engine mounts, the rotor, cap, plug wires and plugs, power steering pump, vapor recovery canister, tie rods, and cold air intake replaced. It has also had the fuel system cleaned. This car has always had a very smooth idle but in the last several months it has developed a vibration at idle. It can be felt through the steering wheel. The vibration is there when the car is in drive, neutral or reverse. Other than that it seems to run fine. Any suggestions? There is one other thing that is odd and I have know idea if it is related at all but I have never experienced this before. The garage door remote stopped working when the engine is running. Turn the engine off and the remote works fine. I have even replaced the remote. The new one does the same thing. I wondered if this was an indication of an electrical issue. Anyway any suggestions would be appreciated.

 

How long ago was the cap, rotor, plugs and wires changed? Were these replaced with Honda parts? Or Autozone parts? Quality does make a difference. Are there any codes? Have you ran the live data stream to see if anything looks out of spec? Engine speed when warmed up should be 750 RPM. If it's a little lower than that you that could be your rough idle. It's possible that your IAC (Idle Air Control) valve might need cleaning. Has the EGR port been cleaned yet? Or are you waiting for an EGR code to pop up. I only mention it, as it will effect idle as well, and it's common for these cars to eventually need the port cleaned once they get some miles on them.
You mentioned replacing motor mounts, which ones? Keep in mind the AT Accords got an electric mount too.

 

The rear mount (low near the middle of the firewall) is vacuum-operated. Look for a vacuum line going to that mount, & follow it to find the solenoid that switches the vacuum on & off. Rotted & leaking vacuum hoses should be replaced.

That mount is supposed to switch into "soft" mode when idling in D or R. Since you feel the vibration in Neutral as well, that doesn't quite fit. But shouldn't stop you from checking the vacuum system for that mount.

First use a MityVac or something to verify the mount itself holds vacuum.
Then hook it back up & test that system like this:
1 - Get a helper you trust that won't run you over.
2 - Start the engine, warm it up.
3 - Shift into D or R while holding the brake.
4 - Unplug the wire from the solenoid valve & notice if the vibration changes.

The vibration should get worse when you unplug the solenoid, and get better when you plug it back in. If it doesn't, you can troubleshoot to decide between a failed solenoid, broken wires somewhere, blown fuse, etc...

 

Another easy check is to stop by a parts store and have them scan for engine codes. Post any codes on here. They start with the letter P and have four numbers, like p1234.

 

Thanks for the suggestions. Did a smoke test on the vacuum system and rear motor mount. No leaks. Checked the solenoid and it was working however could not feel any difference when the solenoid was unplugged. The garage happened to have a 2002 Accord in today and checked it out. It vibrates worse than mine and did not change when the solenoid was unplugged. Mine has 178,000 miles on it and the 2002 has 173,000 miles. Anybody have any thoughts? Could the mount be frozen? Do these models experience problems with the rear mounts when they get a lot of years and miles on them or is there something else that I should be investigating? If the consensus is still that it is the mount how important is it to use a Honda mount versus after market? Everything else that we have checked out has been good. No codes and no miss.

 

This is begining to sound more like an EGR port is trying to close off. Remember, a faulty EGR valve can dump into the intake system and cause a slight rough running.
You mention yours is smoother.

 

EGR was clean. Mechanic is stumped.

 

You may need to look at live data to figure out the problem. Fuel trims are a good place to start. Make sure the car is warmed up. Look at the long and short term fuel trims.

Also verify the battery is good and the alternator is putting out enough voltage. You may want to disconnect and clean all ends of both battery cables with a wire brush.

For the remote, I'm guessing that your are talking about the home link. Does the red light flash when you hit the button to open the garage door?