Rough idle is driving me crazy

**dewok** · 10-08-2008 12:07 PM

I've been experiencing a slightly rough idle intermittently for the past few months. Some days when I start the car it's rough the whole time it's on, other days when started it idles smooth as glass no issues.

I have taken the following steps in trying to resolve:

changed coil packs (hitachi type 'E')
changed pressure regulator valve
changed suction jet pump
vag-com scanned for codes (no codes)
inspected all check valves, visually they look fine. I have not taken them off the hose and tested them though
checked level of all fluids (fine)

My crankcase breather hose was cracked and I had it replaced under warranty, and it looks like the valve cover gasket is leaking (diverter valve hose is pretty disgusting looking)

I had changed the pressure regulator valve and suction jet pump because a leaky valve cover gasket and broken crankcase breather hose tells me something in the line is clogged/broken, but nothing I have done has had any impact.

What's my next step?
Since this happens only most of the time it has to be some sort of valve getting stuck open/closed, or hose that is cracked.

**sloweryucf** · 10-08-2008 05:19 PM

I would take it into the shop instead of spending more money on things that are not broke. I have a similar problem and will let you know what I find out.

I'm thinking it might be the combination valve, a vacuum leak or the fuel filter is clogged.

**aaaudiprotein** · 10-08-2008 06:03 PM

Does it vibrate while shifting? (engine mounts)
Do u have a CEL?

**dewok** · 10-09-2008 01:22 PM

I've taken it to the dealer and a private VW shop and both places have told me that there are no vacuum leaks, and the vibrations are "normal" but I know something isn't right.

The mounts are fine, snub is centered, engine mounts are not leaking.

I am currently in the clean phase of an auto-rx treatment though, maybe after the rinse phase things will level out.

I'm going to test all check valves this weekend just to be sure though...

One thing I noticed is that while the engine is on, if i take off the oil cap there is quite a bit of air blowing out, I was under the assumption that the crankcase should be under a slight vacuum while the engine is idle.

EDIT: no CELs, when it is vibrating it does it all the time, idle, highway speed, shifting

**dewok** · 10-15-2008 09:40 PM

UPDATE: Took it to a shop today to have them replace a leaky valve cover gasket and had them replace the fuel filter while they were at it. No changes in behavior.

today was also the 1,250 mile mark for the first filter replace in my auto-rx treatment and after I was done, idle was smooth, car sounds great.

must have had so much gunk trapped in the oil filter that it was causing the oil pump to work harder, causing a rough idle and loud engine (my amateur opinion).

I set the filter up to drip drain overnight and am going to cut it open tomorrow to check things out, very curious as to what's in there.