As an emissions measure the distributor vacuum takeoff was moved from the
carb to the inlet manifold. This gives maximum vacuum at idle instead of no
vacuum and increases the idle speed, allowing one to back off the idle
screws a little hence reducing fuel consumption and idle emissions. Towards
the end of production the TCSA system was fitted which was to prevent what
Clausager describes as 'surging' and limits vacuum advance to 4th gear only.
But unless it also allowed vacuum through at idle it would remove the
emissions benefit. It would also cause the revs to rise and fall as you
moved the gear lever between neutral and 4th. But then if it did allow the
vacuum through at idle the revs would drop and possibly stall when you
selected 1st i.e. to pull away, so maybe it really does open in 4th only.
Another 'feature' of the solenoid is that when it operates to shut off
vacuum from the manifold it also opens the distributor side to atmosphere,
allowing any vacuum already in the vacuum capsule to dissipate.
If you pulled the hose off the distributor at idle in neutral and heard only
a momentary hiss then that implies the solenoid is closed but the port to
atmosphere is probably blocked. A constant hiss implies the solenoid is
open. If breaking one of the electrical connections to the solenoid makes
no difference it implies a mechanical problem in the solenoid. If breaking
a connection also drops the idle speed to normal that implies the TCSA
switch on the gearbox is stuck closed, which would be cause for concern as
that also locks out the overdrive in reverse, and if it isn't doing that you
could wreck the overdrive.
----- Original Message -----
From: "Steve Gorr" <firstname.lastname@example.org>
Sent: Tuesday, June 08, 2004 6:45 AM
Subject: TCSA & Vacuum advance woes
> .... Pull the hose at the distributor and I
> hear a distinctive hiss and the idle drops back to spec. Isn't the vacuum
> supposed to equalize at some point? The fact that it has to get to 4th to
> trigger the high idle would seem to indicate that the transmission switch
> activating the solenoid properly. Why doesn't the vacuum advance release?
> Solenoid sticking?