Going absolutely INSANE with this intermittent idle shake!! HELP!

[johnny333]

Ok, I still cant find anyone that has posted definite results or findings on their rough idles, and I'm at another dead end. After engine is warmed, idle stays around 750 rpm but the car will intermittently shake with little or no rpm fluctuation. I changed the spark plugs a while ago, didn't fix it. Found small traces of oil in throttle body after popping intercooler off, so changed the PCV, still didn't fix it. Oil is great and all other maintenance is on point. Does anyone have any more ideas? The only next step I cant think of is to replace every hose under the hood or leave it at the mercy of a tuning shop with a surprise $1500 bill to follow. It's a 2006 WRX Limited, BONE STOCK. 77,553 miles. Thanks for any help!!!

[SD_GR]

Is the shake abnormal? Have you compared a similar car?

[mangostick]

my 2010 has a random gentle shiver at Idle.. its had it since I rolled it off the lot at 63 mi and still has it at 90K mi. Its a gentle random shake.. no rpm change or stutter or misfire. I feel it through the driverseat. GF's 07 does it too.. so do a few of the other locals I've talked to about it. Its a 4cyl boxer engine trait.. old VW's do it too. Its just a quirk that comes with the engine design. Nothin to worry about.

[Heide264]

There is normally a bit of shaking in the Subaru idle I have found.

Has it always done this? If so, you are probably okay. Maybe do a few data logging sessions while looking for any detonation or severe fuel trims.

If this is a recent advance, you may consider doing a compression test in the near future - even for just a sanity check. Sometimes blown ringlands show themselves as an intermittently rough idle. Any abnormal colored or odd smelling smoke in the exhaust?

It could be a few routine things as well. If you do some data logging and it comes back with fuel trims across the board, consider cleaning your Mass Air Flow sensor (MAF) and possibly your air filter. If you don't have access to data logging, they would be good to clean regardless.

[zax]

Are you SURE your A/C or defrost isn't on? Also, are you applying any pressure to the brakes?

[MainFrame]

Grounding kit, and install equal length headers. When I put my Perrin ELH on my car that was one of the main things I noticed immediately. When I would stop at lights I couldn't would think my car had died because the idle was so smooth compared to the UEL headers that were on it before.

[Mikie13]

Possibility of tranny or engine mounts starting to wear out?

[drkhead]

This might be a stretch, I'm not sure... but my last car was a 2007 GMC Envoy, and these things need throttle body cleaning every 50-60k or so to smooth out the idle (and give you better MPG & HP).

This happen with subies too?

[johnny333]

There is a little smell of burning oil after shutdown on a hot day, but like I attribute that to the oil that seems to be sneaking past the PCV... I'll heed all the advice given so far and run it through the tests. It's good to hear that it's a common trait. No A/C or defrost, I'll jump on the compression check and cleaning the MAF! Thanks everyone! I'm just one of those guys that's trying to make their car last forever... I drive myself nuts with this stuff. Good thing I don't have kids, they'd be sitting in the doctors office once a week!

[06wrx4me]

I have an 06 TR and mine has done it since the day I bought it 6.5 years ago and still doing it at 87,000 miles. I have found it is much more pronounced when the A/C or defrost is on. It is worse when the headlights and defrost are on.

When I protuned it, it was soo bad that the headlights would dim and almost kill the car. Luckily COBB released a firmware update that allows you to bump idle independent of map flash for both base and idle w/AC on.

I jumped it up 75 RPM or so in both cases.

I also noticed mine got worse as my battery reached death. 3 years ago my car would die when the stumble happened and the headlights were on, so I had my battery tested and I had a dying cell. The car would start just fine and run fine, but when tested the battery was down 250ca or so.

Replaced the battery and it was virtually unnoticeable comparably until a few months ago (when it started getting HOT here). I shut my car off the other day popped the hood to check the belt tension and smelled battery acid venting. I think my battery is on its way out again.

[johnny333]

I've been considering a new battery for the same reason! Thanks! It's got the original battery, maybe it's time to replace before I end up in a jam.

[Front Kick]

My car seems to do that as well. 2004 with 141. Doesn't bother me and never increases as I drive the car so I don't see any problem.