QuestionQUESTION: My Alfa Spider's auxiliary air valve opens too much, so that the cold idle is too fast. If I adjust the overall idle down, the warm idle is too slow. I don't want to mess with the aux air valve adjustment nut. Rather, I would prefer to buy (or fabricate) an adjustable baffling/valve to insert in the aux air valve bypass hose, downstream of the aux air valve (before it re-enters the intake manifold). I would like this device to have a variable opening size, i.e. airflow adjustment.
Any tips? I don't know if you can buy these, or how to make one.
ANSWER: The idle air motor from an 80's SAAB would do it with a pulse generator. However, what do you consider too high a cold idle and what do you consider a warm idle.
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QUESTION: Here's the problem. My new aux air valve is generic and although it looks identical to the original, is probably not calibrated exactly like my 1984 Alfa's original, which was not opening enough. When cold, the new one opens twice as much - I checked. After I installed the new one, first time I started on a cold morning it was idling way too fast, maybe 2000 rpm (have to guess because my tach has been reading low for years), but obviously too fast. It stayed too fast for about 15 minutes because that's how long it took for the valve to close off significantly. (The 12V to warm the device is there - I checked.)
An interesting thing happened during those fifteen minutes - a pronounced pulsing idle developed that I determined was a result of a Jetronic "feature" of cutting off fuel if the idle is detected to be too fast. (When the throttle position sensor is at idle, this feature is active - when engine idle speed dropped low enough it would give it gas again..hence the pulsing idle.) I could bypass this by hardwiring the throttle position sensor to never detect idle, but it still idles too fast when cold. By the way, is this Jetronic idle speed limitation an emissions control?)
I can get the cold idle somewhat under control by adjusting the overall idle WAY down, but then the engine dies when hot.
Someone recommended installing an adjustable airflow restrictor immediately downstream of the aux air valve, which would probably work - but where can I get one / or how do I make one? I want something simple and cheap. And I'd rather not, but if I was going to try to adjust the aux air valve's adjustment nut, how do I set that exactly?
AnswerThe idle fuel cutoff is not an emissions feature. The fuel cut off on deceleration is an emissions and fuel saving feature. You adjust the aux. air valve by loosening the nut and moving the shutter to where you want it--easy to open more but difficult to close down. Easier would be to put a tube with a smaller opening inside the hose downstream or upstream of the air valve. I suspect you have a defective air valve as I have found any old air valve seems to do just fine. The one in my alfa gives me 1200 rpm cold and I forget what it is designed for but not my alfa (probably a Mercedes V-8)
