PAAAAH sound from engine after switching off

[keeweechris]

OK, this is a follow-on from my other 100 topics on trying to fix my dodgy engine, but I just had a thought...

Every time I shut the car off, the engine turns off as expected, then theres a "PAAAAH" sound like 1/2sec afterwards. Sorta the sound of a homo farting ;-)

Never really paid much notice to it, until I thought about vacuum/air leaks being the cause for my engine's woe's. Anyone every heard this before?

Symptoms are:

1) Surging/tugging - most evident when cold, with constant throttle and engine loaded (eg going up a hill)

2) Jerky in transition between acceleration and deacceleration - Ie. when taking foot off gas suddenly it does a few jerks/tugs, and when putting it back on, same thing.

3) If flooring it from low revs, it gives a few jerks/tugs as it climbs up rpm, around 2000-3000 mark I think.

4) Varying idle - not huge variations, just fluctuates a bit. Random shudders too.

5) Crap fuel economy - I know wrx's are bad, but it was getting 400km per tank a year ago, now only 300km. Exhaust smells rich too, to my untrained nose.

Car: 1997 JDM WRX wagon, 195000kms

Mods: Stock except for:

1) Cheap pod filter, but I've got original airbox to put back on.

2) 3" turbo-back exhaust.

I've tried:

1) New O2 sensor

2) Cleaned and tested IACV

3) Tested TPS

4) Relocated Knock sensor

5) Subaru Upper Engine Cleaner multiple times

6) Replaced 2 vacuum pipes that were mildly cracked near manifold

7) Cleaned AFM with electrical cleaner

8) Resoldered AFM internals

9) New spark plugs

10) ECU resets multiple times

I'm thinking air leak at the mo. Anyone heard that PAAAH sound before? Idea's?

Cheers!

[keeweechris]

 CUDDAS said:

have you tried listening with the bonnet up, sounds like it's coming from the pod filter?

Will try listeing tonight.. the wife takes the car to work every day.

If its coming from the pod, what does that suggest?

[Swindog]

its just air left in the system coming out the easiest way it can is it ? My old accord did the same thing, nothing bad ever happened to that.

[DRFVDR]

 keeweechris']

[quote name='CUDDAS said:

have you tried listening with the bonnet up, sounds like it's coming from the pod filter?

/quote]

Will try listeing tonight.. the wife takes the car to work every day.

If its coming from the pod, what does that suggest?

And there is the first problem letting your wife drive it hehehehe

I would so be putting the factory box back on

also maybe replace the AFM (as the symptoms do point to this)

The noise is as said just air coming out,u will not hear it with the factory box installed

[keeweechris]

haha, tell me about it.

[Guest]

My 97 Forester makes the gay farting noise as well as most of the above, I've always put it down to the pod as for the tugging etc I put that down to me not being able to drive manual very well and my 2nd hand manual gearbox and clutch

[Guest]

Have you replaced your fuel filter? to try sort the surging issues?

[keeweechris]

 STi-TypeR said:

Have you replaced your fuel filter?

Yeah, did that a while back. Never made any diff.

Just got the wife to check for the noise. Won't do it now... fukin typical. so its a random thing, just like every other bloody fault on the car. Just show me a damn error code bitch!

[Swindog]

ul prolly find itll only make the air noise once its quite warm. As it trys to pull more air in theres more to be released on shutdown.

[keeweechris]

 Swindog said:

ul prolly find itll only make the air noise once its quite warm. As it trys to pull more air in theres more to be released on shutdown.

OK, thx. I'll figure out where its coming from tonight, but if from air filter, prob nothing to worry about, right?

[Swindog]

wouldnt think so

[Guest boostin]

A/C systems make noise when the compressor shuts off.

[Guest boostcut]

where and why did you relocate the knock sensor?

[keeweechris]

 boostcut said:

where and why did you relocate the knock sensor?

Common mod, apparently. It is said that in older engines the knock sensor picks up noises which it interpretes as knock. Theres a bolt hole further up towards the gearbox-black join which you can bolt it to. Anything was worth a go for me at this stage.

BTW, the gay-fart only seems to happen when engine warm, and comes from air filter.

[Stoffa]

My v5 sti was surging when it was cold, it was only very minor but it did my head in. I changed plugs, AFM and finally water temp sensor, i'm 99% sure it was the water temp sensor that fixed the problem. The best part is it only costs about $20