[T3] '72 FI won't idle down

[Keith Park]

Well, if your at, say, 1/8 throttle accelerating, your going to run leaner
with the idle air bypass than you are without it right?  Remember, this is a
T4, may be a bit different...

Keith


Topnotch Restorations
topnotch at nycap.rr.com
http://www.topnotchresto.com
71 Squareback  “Hothe”
65 Notchback  “El Baja Rojo”
93 RX7  “Redstur”
13 Subaru Outback "Blendin"

-----Original Message-----
From: type3-vwtype3.org <type3-vwtype3.org-bounces at lists.vwtype3.org> On
Behalf Of Jim Adney
Sent: Friday, June 12, 2026 4:27 PM
To: type3 at vwtype3.org
Subject: Re: [T3] '72 FI won't idle down

On 11 Jun 2026 at 22:02, Keith Park wrote:

> Tends to open too quickly when the engine has been shut off and then 
> the idle is too high till it closes AND the engine runs too lean till 
> it closes

If you believe this, do you also believe that opening the throttle leans the
mixture? (It's the same thing.)

The answer to both is, no.

Other systems take input from a throttle position sensor, but our TVS is
just a switch, which doesn't sense position. It has contacts to inject
single pulses of fuel, but no general input on leanness/richness.

Yes, various things add intake air. The pressure sensor and the brain sense
that and respond wth more gas. Yes, it's a primitive system, and the
accomodation is imperfect, but adding air leading to leanness, is just carb
thinking.


--
*******************************
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
*******************************

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