[T3] I'm a bit confused as to why unplugging this IAD temp sensor clears things up.

Jim Adney jadney at vwtype3.org
Thu Apr 4 08:25:30 PDT 2019

On 3 Apr 2019 at 17:10, Jim Adney wrote:

> Not sure about this, but I think a lean mixture burns faster than a rich
> one. If that's correct, a lean mixture would need less advance, not more. 

I just got confirmation that a richer mixture burns SLOWER.

So, at least in the range where the engine is reasonably running, making the 
mixture richer won't compensate for a lack of advance. If anything, that 
would make the timing worse.

BTW, at one point William said that his vac can was broken because he 
could see the broken diaphram, but he later said that he was sure that he 
could demonstrate a bit of vacuum advance by a slight change in advance a 
bit above idle when the vac adv hose was pulled off.

These 2 observations are contradictory. There's no such thing as a weak 
vacuum advance. Check it by sucking on it with a small hose. If the arm pulls 
in and the can holds vacuum, it's good. If the can holds vacuum but the arm 
doesn't pull in, the can is good but the points plate is stuck.

If you can't hold vacuum in the can, the diaphram is broken and you need a 
new can.

The cans are either good or bad. There's nothing in-between.

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

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