Sucking Air ??

[badredwedge]

The 400 runs great but takes a long time to return to idle, I think its sucking air, took the air bypass valve off last night but could not figure out how it works, it is open with the ignition on. Thought I might buy another to see if its working right, any SIMPLE way of testing these things b4 I go and part with my Dollars ?. :spin:

[wedg1e]

The Aux Air Valve should start off open and gradually close as it warms up, reducing the idle speed.
Ah, you knew that
You can test it off the car by poking 12v into it, takes about 5 minutes to close. Sometimes they don't close fully.
It's a rivetted assembly so not really serviceable; don't generally see them on Ebay as most people just sell the full system.
I have a couple of spares if you get stuck...

[badredwedge]

No wedg1e I didnt know that but I do now, so when the engine is hot this valve s/be closed, completly ?? with no airflow past it ??

[chunder]

badredwedge said:

No wedg1e I didnt know that but I do now, so when the engine is hot this valve s/be closed, completly ?? with no airflow past it ??

The disc will close the opening with the engine hot - you can check it from cold by putting 12V across the terminals and then watching it close slowly.
However, if checking by blowing down the hoses attached to it you will find it is only airtight in the direction of airflow when suction is applied to the inlet i.e. manifold vacuum.

If it's on a flapper afm Could it be the overun valve stuck open ?

[blaineuk]

mine will not return to idle until the car has stopped moving, also i wait until it is fully warmed up then switch off and then restart, i find it will idle better then

[thegriff]

yes i am having a high idle 1500rpm when the motor is warmed up.my 400 is of 1989 vintage and has the flapper type meter.been playing around with the overrun valve and found that if it is totally blocked off the idle is a normal 900rpm.got another one on its way to me.