At idle there is vacuum at the bottom of the cannister. Actually feel air being sucked into the cannister thru the drain hose at the bottom of the cannister.
When I put my finger over the drain hose the idle changes and smoothes out.

I notce this a while ago and wondering if anybody else has this issue.
87 TII

 

Purge valve stuck open?

 

I have an 87 NA that has been idling really poorly and i noticed the same thing a few weeks ago. I plugged it up and i didnt notice a change. Im not sure if it is different for a TII though. I havent really looked into it but i want to remove mine completely. But i will see after a little more searching. Good luck btw.

 

If you are talking PCV, it is good.
I actually changed cannisters and still had the same problem.
I am wondering if this should be normal.

 

FD= PCV ( positive crankcase ventilation valve )
FC= purge control valve

two different things with the same initials to do the same job






FD system outline



s4 FC simplified outlay, note the low speed and high speed paths




s4/5 FC purge control valve


the FC uses the purge valve towards the TB at low airflows/loads above idle
and have a secondary high airflow/load system that routes towards aircleaner

if you have strong vacuum at idle then the purge valve purge port maybe incorrectly hooked up to the wrong side of the TB
or potentially the diaphragm in the purge valve torn
this will be obvious by a drop in idle speed if you block the vacuum into the charcoal can

if you have a weak vacuum that does not effect idle speed when blocked then maybe your air-cleaner is blocked or the can faulty


note in the pics the delivery of purge gas is to the front of the TB
,,,and vacuum here at idle should be quite weak,, and stronger with partial throttles
at full throttle the vacuum signal to the purge valve drops off and the high load/airflow circuit takes over

 

I changed the PCV and the cannister and still had vacuum at the bottom of the cannister.
When I use my finger to block the tube at the bottom of the cannister, the ilde speed doesn't change, just that it idles smoother.

 

I will check the hoses to the TB, maybe that's what the issue is.
Just gotta wait until this snowstorm passes.