View Full Version : "vacuum" pipes under idle control valve ???

24th February 2004, 20:32
Yet again, a plea for knowledge !! :rolleyes:

As I was "helping" :eek: change the heads and reinstal the engine, I noticed that under the idle control valve on my UK97-98 there are 2 small vacuum (?) pipes that point towards the passenger compartment. One (nearside IIRC) went to a metal vacuum(?) pipe that had been blocked off, and the offside one had been left open to air.
They are now both open to air and idling is very poor - stalls/dies more often than not.

Wondered what these pipes went to, or were for.
Will block off the one that was blocked off to see if that improves things, but would prefer to know what each pipe was connected to when it was standard !! :confused:


25th February 2004, 11:39
not sure on a 97UK, but on phase 2 MY99 that is where the purge valve is situated. One pipe goes from the plenum to the purge valve, the other goes from the purge valve to the carbon canister.

Has the carbon canister and purge valve been removed?

If so you need to blank off the vacumn hose that goes from the plenum to the purge valve, otherwise its sucking air in under vacumn and leaking air on boost.

Just make sure the vacumn pipe to the Fuel Presure regulator is connected too, you could melt the engine if it's not.

25th February 2004, 19:02
Thanks John.
Carbon canister has been removed.
??plenum?? what/where is that ? Is the purge valve a separate entity from the idle control valve assembly ?
AFR, knock and boost all reading "normally" (Jeffrey Archer novels last time I looked :rolleyes: )

Blocked off the pipe I thought was blocked off before engine removed and tick over seems improved on minimal test on the way home tonight.

[ 25. February 2004, 07:07 PM: Message edited by: StanS ]

25th February 2004, 21:06
plenum = inlet manifold basically.. where all the vacumm pipe take off

1st March 2004, 20:03
Cheers JGM !
Its an age thing - I am used to inlet manifold being called inlet manifold, and exhaust manifold not being called headers ! :rolleyes:
All pipes on inlet manifold accounted for (none "open" to air).

Still struggling to find where these "vacuum" pipes are supposed to go !


1st March 2004, 20:40
Are you able to take some pictures??

Sounds like it could be the two pipes from the carbon canistor.. or rather than were connected to it..

on idle do any of the pipes suck??

I have removed my carbon canistor and have two pipes left open to atmosphere, one is the vent from the fuel tank and the other a vent from somewhere else (cannot remember lol)
They are both below the alternator though, I have retained the one way vavle that was on one between it and the carbon canitor, then T'd them together and fed the pipe into the chassic rail where the carbon canister used to vent.


2nd March 2004, 19:49
Hi Simon,
Pictures may be tricky as there is a limited tunnel to view under there !

I removed a lot of the small vacuum pipes under the inlet manifold when I did the intake pipe and removed the C canister. (I originally just "T'd" the C canister pipes together.)
The vent from the petrol tank I have blocked off -I thought the tank was holding + pressure anyway.

Under my idle CV there is a reddy-brown plastic moulding with 2 vacuum pipe size pipes pointing horizontally back towards the passenger compartment. One (near side IIRC) is slightly longer than the other.
I will try to see if they suck/blow !
Would the connections be shown on a w/shop manual ?

Tone Loc
2nd March 2004, 20:47
That brown thing is your purge control valve. One connection goes to the top of the throttle body and the other goes to the carbon canister (via a section of metal pipe which is connected to the orginal metal fuel lines.

Basically as John said at the top of the thread ;) .


4th March 2004, 07:44
Cheers Tony,
As no-one answered my earlier question as to what or where the purge control valve was, I was unable to make progress understanding what John said ! :(
Now, after all this time I know !!
Thanks !!

4th March 2004, 18:13
sorry stan, i missed your question.

shout louder if you dont get a reply to a part of your questions, it's easy to go word blind sometimes. :D

4th March 2004, 19:48
Hi John,
I don't like pestering people with what to them are dumb questions - especially as I assume they are up to their ears in their own problems !!

As always, I am VERY grateful for any help/advice I am given by those who know the answers and who take the time to reply. (so thanks again ! smile.gif )

Found that the pipe on top of the inlet manifold had been blanked off, but still didn't know which pipe on the purge valve to connect that take off to, so I connected pipes to both the purge valve pipes and tried sucking and blowing hard with ign off and then on tick over to try to work out which way this valve worked, checking if anything came in/out of the other pipe, but I could get no flow under any conditions - as though it was blocked!
So still don't know which of the 2 purge valve pipes to connect to the inlet manifold !! :(
But progress is being made !! :D
Will ask new question - what does the purge valve do, and if there is no carbon canister is it needed !! ?

[ 05. March 2004, 07:17 PM: Message edited by: StanS ]