Revs drop ???

[ex_scoobydoo]

i just had my service done on saterday, found a couple of split pipes, replaced them, replaced the oild plugs and filter the car seems to be running ok but
i have noticed now when i come to a junction and drop the clutch the revs drop and the engine nearly stalls then they spring back to normall just below the 1000 mark has anyone had this problem or any idea what it could be, it only happens when i drop the clutch and stop apart from that it seems ok.

 

[rossbrownlee]

Hi mate.
not sure on this or even if it is fitted to your car but I believe that there can be an issue with the vacuum servo/assist for the brakes that can have an effect on the car when you are at low revs/idling and brake i.e. coming to a junction.
sit stationary at idle and pump the brakes a few times and see what happens?

 

[ex_scoobydoo]

ok i will try that, the car drops to about 200 then shoots straight back up to around 800 then idles fine, but i have also noticed on low revs or off boost sometimes the car seems abit jittery, i dont know if all s3,s are like this or just mine.

 

[ex_scoobydoo]

exactly what you said mate
if i sit stationary and rev up on they way back down they drop to around 400 then spring back to around 800 were they should be, if i pump the brakes whilst they on the way back down, everything is fine, they come down nice and smooth and settel @ 800 once i stop pumping they drop again so yes its what you said, i think, were is the part located on the engine do you know ?

 

[ex_scoobydoo]

ok guys i may have found the problem, but im not sure of the fix
when i said i fixed 2 split pipes, well one of them was the 3 way splitter was snaped, so for a temp fix i used some strong silicone and a bit of copper brake line to improvise, so today i disconected it and the revs are now fine, im not sure what this pipe is for, its one of the two pipes that run down the front of the engine, i can feel it sucking air, but when i rejoin thats when i have the revs problem, i have taken i little picture and circled in red the 2 pipes as they are disconected, i hope someone understands and can shed some light on the problem

 

[Dani_B19]

Thats the n249 system and im not 100% but that pipe thats broke could be the part that controls the DV, just buy a plastic t-piece and fit it, problem solved.

 

[ex_scoobydoo]

i would think the temp fix would work aswell, unless the t piece is special in some way, or something else is maybe wrong i will try a new t piece ofcourse

 

[rossbrownlee]

It is the same area as the vacuum supplt to the DV but that is off a different hose (the one with the chunky spacer on it iirc).
I think the smaller hose runs from the intake manifold to the tee-piece as the source of vacuum, and the fat hose actuates the black plastic valve and supplies vacuum to the N249 valve (where it ties on at the same end of the SOV as the electrical connector).
You could go to your local dealer and speak nicely to one of the mechanics directly try and scrounge a bit of hose, or just buy some bits from your local factor / halfords etc.
If you buy the bits mind and make sure they are secure with hose clips etc as the hose will be pressurised under boost as well as being vacuum.

Of course, that is assuming I have the right hose.... highly doubtful!!

 

[ex_scoobydoo]

i think thier is still some other problem, the temp t piece i made is air tight, when i connect the pipe up then the problem starts with the revs dropping, at the moment im running it disconected, but i still think even with a new t piece it wil still be the same, what else could be the reason ?
could it be the actual N249 valve thats at fault

 

[rossbrownlee]

well this is a complete and utter guess, but possibly your ecu is confused due to your engine being able to suck in air directly to the intake manifold, bypassing all the metering etc?
May be that the engine management needs to adapt once you have fixed the pipe.
but as I said - complete and utter guess.

 

[ex_scoobydoo]

mmm maybe but i did run it all day yesterday connected, i would guess that would of been enough time to adjust, il pop down to the motor factors now to buy a t piece. see what happens

 

[Dani_B19]

You didnt get silicone into the pipes did you? Could have caused a blockage.

 

[ex_scoobydoo]

nope is all clear i have checked them and bought a new t piece, still the same

 

[Dani_B19]

Does it drive normaly, comes on boost, holds boost etc?

 

[ex_scoobydoo]

yer everything seems fine apart from that
well sometimes in second gear at low revs say if i slow right down to come around a tight corner it is a bit jittery speeding back up but only sometimes, only off boost

 

[s3ollie]

sound like the same as when the MAFs not connected

 

[ex_scoobydoo]

Hi mate.
not sure on this or even if it is fitted to your car but I believe that there can be an issue with the vacuum servo/assist for the brakes that can have an effect on the car when you are at low revs/idling and brake i.e. coming to a junction.
sit stationary at idle and pump the brakes a few times and see what happens?

well after looking round more i think this is my problem, when i pump the brakes it doesnt happen, so does anyone know what part i need if its not expensive i will buy and try see what happens.