Very rough engine vibration only at idle

FIREBANANA

MEMBER
2002 VOLKSWAGEN JETTA
2.0L
4 CYL
FWD
MANUAL
122,000 MILES

Very rough vibration at idle. Engine does not miss and stays steady at 800 rpm, but engine vibration is shaking entire car. Runs well at speed, pulls strong, no misfires or bogging under load. Oil looks good. Fuel pressure is good at 35-38 psi at idle. Used multiple bottles of fuel system cleaner to date. Cleaned MAF. Recently replaced downstream O2 sensor, plugs, wires, coil pack. Replaced crank position sensor six months ago. Replaced all motor mounts twelve months ago. Not sure what to do next: check compression, replace injectors, replace fuel pressure regulator, replace MAF, check for vacuum leak (how)? I do not want to throw money at random parts.

Car starts right up, pulls strong. Getting twenty four mpg (which is lower than it should be).

1 Reply

CARADIODOC

MECHANIC
33,916 POSTS

You said the engine is not misfiring, then you listed all kinds of things that address misfires.

Idle speed alone can not be used as a misfire indicator. That is controlled by the Engine Computer, and it compensates for a number of variables that would otherwise reduce speed. The idle speed system on Chrysler products has enough control to maintain the desired idle speed when six injectors are unplugged on a V-8 engine. Believe me, you will feel the misfire vibration, but idle speed will be exactly at specs. Your idle speed will also be correct if one cylinder is misfiring.

If you think the engine does not have a misfire, look for a collapsed engine mount that is allowing the two metal parts to rub or contact each other. That will transmit normal engine vibration into the passenger compartment.