A little info on my car first:

S5 13bt, stock motor, stock injectors, front mount intercooled, 3" exhaust, and tuned with SAFC II on stock ECU

Was driving to work today and my engine started idling inconsistently, between 680-750rpms at 15Hg vacuum (which it normally runs around 15-17Hg vacuum), I could tell it was just idling weirdly.. and further down the road, the engine started doing the infamous paint-machine shake and idled consistently at 1400rpms with a consistent vacuum of 12Hg. It got me to work, and seemed to run fine while under load but it 'felt' like it had less power, but I stayed completely out of boost. Not sure if it helps to include, but I was not getting any knock readings while driving or idling, even after the idle and vacuum changed.

I'm doing a compression check when I get home, if it gets me home, but just wanted to pick your guys' brains. Could it also be a stuck injector, bad plug, or a vacuum issue?

 

Update:

Let it sit for a while at work, turned it back on and it started to idle fine again. Back to 16Hg vacuum and 750rpms consistently. I'm thinking possibly a sticking injector and carbon build up causing sticking seals?

 

decarb
change spark plugs/wires if they are older
change the fuel filter if it has over 30k on it
check and clean grounds at rear rotor housing, on the starter and at the battery

additionally i would do a TPS sweep test to see if it is failing

 

Fuel Filter is about 10k miles old
Bought some seafoam, going to run it through a vacuum line and put the rest in the gas tank.
TPS sweep will be donight when i get home too.
New plugs would be a good idea, and I'll check the grounds.


Will premix cause more carbon build up?

 

premix causes less carbon buildup.