Shaking at low revs (Bugeye WRX)
 

Just last week my Scooby started shaking noticeably at low revs - usually when coming to a stop when driving around town. Continues for a couple of seconds once the car has come to a stop so I don't think it's wheel bearings or drive shafts. Doesn't feel right, really can't describe it any better than that :lol1:

Also it sometimes makes a slight crunch/scraping sound while slowing down, especially while driving down a slight slope.

Doesn't seem to be clutch, as that was replaced only a few weeks ago (Exedy uprated) and messing with the clutch pedal doesn't affect the rumbling. However I noticed earlier that you can feel the vibrations quite strongly through the gearstick. Seems to go into gear ok though with no crunches etc. :confused: However I've noticed since owning the car (about a month) that when reversing onto a low curb at home while steering and maneuvering sometimes it makes dodgy noises and I swear one of the wheels spins and something bangs/whirrs. Very odd. I sort of just let it be because I spend maybe 30 seconds a day reversing lol

All of these symptoms seem to only happen after a couple of minutes of driving, so when things start to warm up. Coolant and engine oil are both fine, mechanic should've sorted out gearbox and diff oil when the clutch was done but would they be the cause potentially?

Could it be a clogged filter? Faulty sensor? The first thing when I typed 'shaking at low revs' into Google was dead cylinder so I'm a bit worried haha

Still seems to be pulling very well, not smoking alarmingly, no warning codes except for the bloody airbag light which is temperamental. I'm even wondering if the engine mounts are knackered? It feels like someone has dropped a lumpy old V8 in when I wasn't looking lol

I don't know if it's because I'm just not used to driving a 313hp car, but when you floor it through the gears either the clutch is slipping (unlikely as it's a brand new clutch) or I'm not getting the sort of traction I was expecting.

Sorry I can't give a description of the fault more accurately - I find it quite difficult to put into words. Just reading through all of the above I think I'm on the way to answering my own question - sounds like diff problems :(

My car shakes at tickover only, due to uneven compression. Borewash or damaged ring through a broken spark plug, incorrectly operating injector or bad map caused it, the respectable Subaru Specialist diagnosing the shake couldn't tell me which.

Best go get it checked over mate sounds like it all needs diagnosing on the car, may be a number of things going on.
Lumpy tick over could just be the cold weather and rich mixture for warm up if it clears as engine temps come up. But might be failing ignition or plug or low compression on a cylinder or even out of balance flywheel.
The crunch/bang/whir is a worry if it didn't do before clutch change. I would go straight back to that mechanic and also mention possible slipping clutch. To check if the clutch is slipping stick it in 4th at about 60mph floor the accelerator and dip the clutch and release if the revs don't drop as soon as you release then clutch is not up to the job and he may have fitted a cheap copy or you are getting oil on it. Has he defo put your box back in as if the diffs aren't matched you will get all sorts of weird noises.

To stop airbag light,put 3ohm resistor in plug under front seats. Check little hose hasn't came off dumpvalve,it will struggle to tick over if this is off

If maf is unplugged (or faulty) car will shake.maybe worse when cold. Or engine coolant temperature sensor faulty (this controls fueling by reading engine temp.its like an automatic choke basically). Or even iacv (idle air control valve) this is on top of throttle/butterfly. Throttle position sensor is on the side and iacv is on top.