164 surging Minimax throttle switch

[C M Smith <cmsmith@domain.elided>]

This happened to my 91 early on. The throttle position switch is the small 
black "box" on the throttle housing. It can get a tiny bit out of 
adjustment giving the symptoms you describe.

The box is held in place with two machine screws holding the unit on with 
slotted tabs. The slots provide adjustment.

With the engine off, loosen the screws just enough to allow you to slide 
the switch. Then slide it very slowly one direction until you feel a tiny 
click. You may have to slide it both directions to get this right, I cannot 
remember which way it rotates to close the switch. The click you feel is 
the minimum switch opening. This is the idle setting switch which cuts out 
the engine ECU mapping and substitutes the special lean idle mapping. The 
02 sensor feedback does not operate at idle. Then as you crack the throttle 
open this minimum switch opens, enriching the mixture for normal running 
and re engaging the O2 sensor feedback loop. If the switch opens too early 
the idle jumps up as the mixture is enriched, without you changing the 
throttle position.

What you want is for the switch to just close as the throttle returns to 
idle position, the accelerator cable must be adjusted correctly before this 
is done (though I never heard of it going out of adjustment, it's a 
possibility). There is another micro switch in the box which enriches the 
mixture when full throttle is used (actually more than 75% open) and again 
the O2 sensor is bypassed as the FPR ups the fuel pressure and full 
throttle enrichment is engaged. I try to drive my 164 this way as much as 
possible, foot hard down makes a huge difference to the power output, out 
of all proportion to merely the opening of the throttle.

When this happened to me, I was next to a guy and his girlfriend in a 
tinbox jap car, waiting for the green light,  and my 164 started to rev the 
engine up and down like I was challenging this guy to a race, too funny. 
I've always said Alfa's have personality and apparently they don't like 
Japanese cars much. Good job I got it fixed before I was in a similar 
position with a police car. Oh yes, my 164 did win that stoplight GP. I had 
to help the old girl by actually standing on the gas when the light 
changed, but having cast down the gauntlet I could hardly let her down eh?

Cheers


Michael Smith
White 1991 164L
Original owner
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