I just got my car back together a few days ago after doing a transmission swap and oil pan gasket. I noticed when the car is in gear and idling, the front end shakes a lot. I just recently replaced the front motor mount and used a polyurethane insert on it. When I rev the car a little bit the shake goes away. How can I diagnose this vibration or shake? Any ideas or insight would be appreciated. Thanks in advance.

-Scott
97 Accord Se 192,000miles

 

What is idle speed in gear? If it's less than 700 rpm, it's probably too low. Usually the Idle Air Control Valve (IACV) is the problem due to dirt/grease/carbon buildup. A good cleaning of IACV, throttle body bore near entrance, and both sides of throttle plate will allow IACV to control idle speed correctly and elminate low idle vibration.

Given your work it's possible the rear, vacuum controlled motor mount was not connected correctly. Check the vacuum lines and vacuum switching solenoid valve for function at idle; open valve and vacuum to mount.

good luck

 

Actually the idle speed is steady at 650-700 rpm. Update.... I checked the rear motor mount and found the actuator rod was broken on the rear mount assembly. The vacuum actuator works fine, I tried running the vehicle and moving the lever, but the car still vibrates like hell. Is it good to assume the mount is no good? Do I need an OEM replacement or will a aftermarket suffice?

-Scott
97 Accord 192k miles

 

Mostly the aftermarket replacements are stiff, performance-oriented mounts. You want to find an aftermarket one that's a duplicate of the stock factory mount.

 

There was a recent thread on this site about an aftermarket vacuum-switch mount that was far too stiff and caused vibration. Vibration was cured w/ an OEM replacement (used I think).

Your idle speed suggests the IACV and throttle body cleaning might be helpful. IACV should compensate for load changes; a/c, alternator, and transmission load.

good luck

 

Yeah, that thread is why I warned him. Someone bought a rear mount that turned out to be very stiff. Good for engines making more torque than stock, but bad for vibrations.

I think that mount from that thread did NOT have the vacuum-operated feature anyway.

 

I just got through replacing my rear vacuum activated mount, and I fired her up again and as I was backing out the front end did the same old thing again, shook the front end still. So now, the front and rear mounts are new, the left and right mounts are still original mounts. I havent sprayed the IAC yet. I do have a front polyurethane insert that I installed when I installed my front mount because my mount collapsed. I havent heard anything about that being a problem for anyone else. I dont suspect an engine performance issue because the motor is sound. It only gets bad when its in drive. Any ideas?

 

Try removing the IACV electrical connector and observe idle engine speed. It should drop to 550 +/- 50 rpm (check engine light will come on, pull BackUp fuse for 15 secs to reset). If idle speed doesn't drop, the IACV is not opening to provide idle air and needs cleaning/replacing. You may need to clean IACV and throttle body and perform idle speed setting w/ the air bypass bleed screw.

good luck

 

I just got through testing the IACV via unplug method. The idle lowered significantly, so the IACV should be working. What would be good to check next?

 

How much, exactly? The base idle should be 550 or so, it's not good for it to be too high.