d_hipperson

Hi folks, I've been lurking for a while but I now need to make my first post so here goes.

Firstly, I have searched this forum and others for advice but I'm rather stumped as my symptoms don't match anything I've read about.
The car is a stock 2006 Hawkeye WRX with circa 60K miles and has never missed a beat but she has suddentlly developed a fault.

Symptom 1) No obvious misfire, but it won't hold steady revs. For example, in neutral if I advance the throttle to approximately 2000 rpm, it can't sustain it. The revs cycle down by 500rpm and then back up with a period of a few seconds. This occurs throughout the rev range and manifests as juddering when driving.

Symptom 2) My boost/vacuum gauge takes around 5 seconds to return to 0 when the engine is turned off. It always used to return to zero instantly (as you'd expect). What could be preventing the vacuum from decaying?

I'd consider engine knock or mechanical problem if it weren't for the weird vacuum decay issue. Subaru indicated to me last week at the service that the MAF sensor was giving fluctuating readings so I replaced that. No difference (it was probably the rev hunting that was causing the fluctuating readings methinks).

There are no trouble codes stored or indicated.

Checked vacuum hoses. Spark plugs are 10000 miles old.
I've bought an ELM327 wifi OBD2 dongle and an iOS app called EODB-Facile. I don't really see anything obvious wrong other than the periodic rev drop.

If anyone can tie together these symptoms I'd be very grateful for any ideas! Or further troubleshooting steps.
Many thanks!
Hippo

Beastie

iTrader: (2)

Sounds like you have a blockage in your inlet ducting/air filter.

Or a collapsing hose under vacuum (Which is common with aftermarket hoses)

Have you fitted an aftermarket air filter?

d_hipperson

Hi Beastie, thanks for your reply. I have standard hoses and a K&N panel filter. I shall check the state of the filter as soon as the weather clears!

Cheers

Dan