D jet cold idle speed, aux air valve?

[Drew20]

my coupe idles at 2000rpm when cold, which seems high. What rpms should it idle at, cold and warm?

I've done a bit of reading on this site and it seems the common issue with the aux air valve (airslide valve) is the wax capsule ages and fails to close the airflow off when warm. I seem to have the opposite issue where the valve is open too wide when cold. I could not see any way to adjust idle speed during warm up, except through the normal throttle body bypass, which would of course impact on the normal idle speed also.

Grateful for any info, hints or tips

 

[Dan Mooney]

my coupe idles at 2000rpm when cold, which seems high. What rpms should it idle at, cold and warm?

I've done a bit of reading on this site and it seems the common issue with the aux air valve (airslide valve) is the wax capsule ages and fails to close the airflow off when warm. I seem to have the opposite issue where the valve is open too wide when cold. I could not see any way to adjust idle speed during warm up, except through the normal throttle body bypass, which would of course impact on the normal idle speed also.

Grateful for any info, hints or tips

Hi Drew,

I had the same problem with my CSi when I first got the car a few months ago. You can confirm the Bosch auxillary slide valve is the culprit, and potentially cure your idle issue, by taking the valve out of the loop by simply capping off the system at the manifold port (see attached photo).

I have a new slide valve on order with Carl Nelson but frankly the car is running great without it, hot or cold. My car idles at a steady 750 rpm and always starts first time without the slide valve.

Hope this helps!
Dan

Note: The photo below shows the port at the manifold, not the air slide valve, which lives down below on the left side of the engine block.

 

[Drew20]

That's interesting Dan, I will give that a go. My Haynes (E3) states idle speed of 850-1000, but I'm sure this will be warmed up spec only

Is that rubber port cap a special thing I can buy, or something you made yourself? I've not seen one

 

[Christopher]

Dan / Drew - that isn't your aux air valve, that's the cold start valve. The air valve is directly under this

 

[Drew20]

yes, what I think Dan has done is cap off the pipe running between the AAV and the port into the airbox/ induction unit, so taking the AAV out of the system altogether. The AAV connects to the airbox where Dan has put the rubber cap over the port.

The CSV attaches to this same port, ie so on a cold start the extra fuel comes into the airbox at the same point as the extra air

 

[Dan Mooney]

Dan / Drew - that isn't your aux air valve, that's the cold start valve. The air valve is directly under this

Hi Christopher, I am aware that the photograph I showed Drew was not the air slide valve. I was trying to demonstrate how he could take the air slide valve out of the loop by capping the port at the manifold.

My air slide valve is pictured below.

 

[Dan Mooney]

That's interesting Dan, I will give that a go. My Haynes (E3) states idle speed of 850-1000, but I'm sure this will be warmed up spec only

Is that rubber port cap a special thing I can buy, or something you made yourself? I've not seen one

Nothing special, Drew, just an appropriately sized rubber cap from one of my mechanic's 'odds and sods' tool box drawer.

If you have a helper, pulling the hose from the port at the manifold while the engine is running and immediately blocking it off with a finger will tell you if you are on the right track. My guess is your rpm will rise dramatically when you pull the hose off, then return to a much lower level when you block off the port. The dramatic rise in rpm is why you need a helper, one to play with the port, one to be ready to shut the engine off quickly.

Good luck!

 

[Drew20]

Thanks Dan

If I have a helper we can polish a nice bottle of something and whack the cork into the port!!

 

[lloyd]

FWIW:

The auxiliary air valve and cold start injection have been discussed on this (and other) forums several times. This includes air valve alternatives and even (possible) repair. https://www.e9coupe.com/forum/threads/help-a-friend-injection-iddle-valve.12086/ Search function can be your friend: e.g., https://www.e9coupe.com/forum/threads/d-jet-csi-auxiliary-air-valve-element-on-ebay.21629/

Plugging the auxiliary air valve's plumbing forward of the manifold and bypassing the valve's function is a common stop-gap fix. However, you have to remember to address the fuel feed to the cold start injector. Otherwise, it will result in an unnecessarily ultra-rich fuel mixture and create its own related issues. Temporarily disconnecting the electrical connection at the valve should shut the fuel supply. However, on the off chance the valve is not fully seating - and dribbles fuel into the manifold - that also creates running issues.

Most people are content to stick with the original equipment. Still, as food for thought, I vaguely recall seeing a mechanical choke, possibly from a motorcycle carburetor, being adapted to the auxiliary air valve on an E3 to replace the sliding piston. I have no idea how well it functioned, but the concept did not seem that far fetched. Air cooled engines fitted with Djet injection and later M30 engines fitted with Ljet injection employed bimetallic electronic air valves and/or a hybrid version of the valve controlled by coolant temperature and time-sensitive electronics.http://www.firstfives.org/faq/aux_air_valve/aux_air_valve.html