Exhaust leak and revs rising between gear changes
 

Over the last few days I've noticed a flickering sound coming from under the car, and it turns out that the cat and the downpipe aren't fully connected properly. One of the two bolts have somehow come loose so they're no longer connected properly.

Could this be the cause of my revs rising inbetween gear shifts at all? I'm having to lift off the throttle, wait a bit, and then change gear to avoid the revs rising slightly.

Interested to see what people reckon to this, I have to do the same to change gear...assumed it was just my driving ability...

I've done a lot of research and a lot of people are saying it's built into the ECU with the newage cars - even the cable throttle driven ones. However, if I reset the ECU the problem goes away temporarily, so...

I replaced the IACV recently and that has helped, but the problem is still there. It's not there when I'm on full boost WOT? Just when cruising.

Yeah I did a quick search and that seems to be the consensus.

I'm planning on cleaning out the IACV and throttle body to see if that helps.

Long term though people seem to believe it can be mapped out, so once I find some decat pipes I'll get a remap and hopefully that will sort it. It's the most irritating thing about the car, really gets on my nerves!

It can be mapped out on the newer cars with DBW, but I had my map checked by Bob at BRDevelopments and he couldn't see anything that would cause this issue.

What scoob do you have?

Ah right, well I have a 55 plate blob WRX wagon, so not DBW unfortunately.

Have you tried cleaning out your throttle body?

No because that's a mechanical aspect of the car. If I reset the ECU the problem goes away and then comes back later, so I can't see it being a sticky throttle body, throttle cable or the clutch (as I've seen suggested elsewhere).. It's a tough one!

Do you have a standard recirc valve or an atmospheric one?

If the problem goes away with a reset but returns after a period of driving then maybe a faulty lambda? This sensor is used in closed loop fueling for your learning tables,might be adding fuel when it doesn't need to?
Can you data log and view LTVs?

Well if replacing the IACV helped, I can't imagine cleaning the TB would hurt. I'll be doing it as a matter of course soon anyway, so I'll let you know if it helps.

I'm running a dual port (GFB Respons), currently set to 50/50 recirc/vent. I noticed it before I fitted that though, although I think the valve may have made things worse... :wonder:

How can I data log? Can I do this through the Torque app?

I did think it might have been a faulty lambda, but wouldn't I have a code come up when I do a diagnostics test?

I could do, but it doesn't make sense to me. It's something electrical that gets reset and then re-learns something it shouldn't.. Let me know how it goes anyway.

Yeah the standard valves are known to leak as well, but aftermarket ones do make things worse :lol1:

I have a 2002 WRX PPP, 175k and can't say I've ever noticed this issue. Which would suggest that it's mechanical or only effects >02 ECUs. Can you try datalogging to help with identification.

Not always picked up as a fault if it's a failing sensor,you say it doesn't do it on WOT on load so only happens in closed loop which is where the lambda is used to learn fueling adjustments.
Not sure you can log with app doubt it.
A simple vag com cable and romraider should do the trick.

Do these cars just have the one lambda? For some reason I think they have two.. Are they easy to swap out yourself?

2 sensors. 1 pre turbo and one post. The post one doesn't effect running as it's basically there to test whether the CAT is working. The pre one will effect running. In theory they are easy to change. A crow's foot spanner or sensor removal tool will help (cheap to buy). However, when I tried to remove mine, it wouldn't budge. Got a garage to do it and they had to retap the threads to fit the new one.

Only ever replace with genuine Denso sensors.

My map doesn't have pops and bangs yet sometimes it can be quite poppy (if that makes sense) in the low revs on decel. Could this be a result of a failing o2?

Is this what I want?
http://www.ebay.co.uk/itm/FOR-SUBARU...AAAOSw9NdXqwQj

This looks like an easy guide too - https://forums.nasioc.com/forums/sho....php?t=1839895

Looks like the correct sensor but I have a classic with just one lambda so worth double checking.
Popping on the overrun could be a sign of overfueling.
Tbh before I splashed out on a sensor I would be tempted to buy a cheap cable and do some logging,check LTVs etc,probably get a cable for under a tenner and it will be one of the best tools you can have,being able to see the data from your ECU can tell a good story and diagnose many problems.

Will the vag-com cable even work on subarus?

Yes

Cool - I've ordered one and will post the data logging and LTVs if I can't work out anything myself. Cheers

Went out for a blast last night and forgot to mention that if I change gears fast and slam on the accelerator there's a slight hesitation before the power comes in.. So it's not completely fine WOT..

Could this still be the lambda, or something struggling to keep up?

I would think the lambda could affect that,when you come off throttle it will switch to closed loop,I'm not 100% sure how fast the transition from open loop to closed loop is but if it's dumping a little more fuel than it should then it'll will be rich and maybe bogging down slightly,does the hesitation happen straight after a reset as well?

Your best posting some logs and LTVs in the engine management section when you get your cable,there are a few very knowlagable and helpful members like bludgod and Bob Rawle who could look through and spot the fault straight away.

I did reset it last night, but only noticed it towards the end, but I'll have to double check.

Okay will do, thanks for your help so far! Much appreciated

Gonna revive this thread in the hopes that you had more luck than me in solving this SubieJack?

Cleaned out my TB/ICV and not really made much difference to the problem (although it does idle more happily now!). I'm using the car more often now, and I'm learning to drive around it but would really like to get it sorted if I can!

Hey mate,

I changed the IACV on mine with no difference too! Thank god i found a 2nd hand one, as a brand new one was £200..

I actually ended up changing the front O2 sensor on my car at the weekend - hoping this is it, as I can't think of anything else after that. It's been only a day since I've reset it, and it usually comes back after a few, so I will let you know if it does or doesn't.

I have this on different car

think its tiny hole in crook of 4/1 manifold

Had a leak on my up pipe and it caused the car to idle erratically and cut out etc.

Funny you say that - When I'm accelerating normally I can hear a flicking coming from the side of the car.. I had an exhaust leak checked, and it was fixed, but there's clearly another.

I take it the flickering sound of air is an exhaust leak..

Luckily my IACV was fine, just caked in black crap! Just gave it a good cleanout with carb cleaner and it came up good as new.

Oh ok, well let me know how you get on! I think it might be O2 sensor as well to be honest.