vsalvato

I need an expert opinion: My S4/MY88 has been affected since long time by idle instability; the problem appears now to be fixed (hopefully) but the engine still stalls on idle, from time to time. I was at the garage today and the mechanic show me a tube coming out of the intake manifold which he has no clue to what needs to be attached; here are the pictures:

The chart in the workshop manual at par 24-216, volume 1A shows a 4 ways valve (and 4 tubes originated from that) but my car seems to have 5 tubes; any idea where the 5th tube 9the one in the picture) should be connected to? My mechanic guess is that something was removed from the car by the former owner(s), eventually an active carbon filter (which he cannot trace out in my car)... any other guess?


Thanks in advance for help

Leon Speed

Do you have an auto or a manual gearbox?

SteveG

Maybe this will help.

vsalvato

AT!

Leon Speed

Ok, from the location it either goes to the transmission or to the charcoal cannister vacuum valve.

If your gear changes are clunky, it might be the connection to the trans.

The charcoal cannister vacuum valve sits against the inside of the engine bay, in front of the cooling tank. It has a hose which connects to the inside of the passenger fender, where the charcoal cannister is located. You need to take off the wheel and fender lining to get to the charcoal cannister. The vacuum valve can be reached from within the engine bay.

A third possibility is the fuel pressure regulator but from your picture it looks like there's a vacuum line connected.

vsalvato

Tks for the vaccuum diagram; I understand that this could be an extra tee for vacuum feed to AT, why is then detached and what would be the effect of it being detached? Can you pls detail where it has to be connected

vsalvato

Aryan, indeed the last time I drove it the gear changers were very clunchy (never been before...); you might have hit right!!!! Tks indeed... where is the tee supposed to connect?

Leon Speed

Vacuum modulator, transmission drivers side: https://rennlist.com/forums/3405134-post2.html

The charcoal cannister vacuum valve can be seen here, pic 5 (under the washer tank cap): https://rennlist.com/forums/7744322-post28.html

vsalvato

I was at teh garage half an hr ago; he said the AT tee is connected, hence the lose tee must be that of the Canister but he says the charcoal canister is not there, must have been removed... is it possible? what's the function of the Charcolal Canister, is it critical?

fraggle

Emissions equipment. If not removed "properly" you may have issues with fuel tank venting.

WallyP

The charcoal cannister is hidden away inside the right front fender - it is not in the engine compartment. The valve that controls air flow/venting for the cannister is in the engine compartment.

vsalvato

The guy at the garage confirmed that the Carbon canister is missing;asmuch as I understand this shoudl not have side effects other than that the vapours from the fuel tank will be released to the open air rather than recycled through the carbon filter and from this to the intake manifold? Am I right with the assumption that I can manage with the missing carbon canister? I bought the car in Germany a couple of years ago and besides a stubborn idle hunting and engine stalling issue which has been bothering me since 12 months the car was running OK prior to that.

Leon Speed

Yes you can do without the charcoal cannister, unless laws in your country prohibit tank venting into the open air. Operationwise it should not matter. I don't want to second guess your mechanic (ok actually I do ), but are you/is he sure? It is very uncommon for it to be missing (unless there was a collision requiring the right fender to be replaced). Did your mechanic remove the right front wheel and did he remove the fender inside liner to check if the cannister was there? If so make sure the hose between the cannister and the engine crank case (runs in front of the engine) is also plugged.