Very Low Warm Idle

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Tyler

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Hi All - I have a well-running stock D-jet EFI, except the idle drops very low (ie, 100-300 rpm) when the engine is warm. It never dies, and doesn't even sound overly rough at that level, but I don't think its supposed to fall that low.

Throttle response is very good, even from the low idle, and power is strong across the full rpm range.

Idle during warm-up is around 1,000-1,100 rpm, which seems normal.

Any help in narrowing down the problem (if there even is one) is much appreciated.

Regards,
Tyler
'73 CSL Inka
London
 
Hello Tyler,
From what you describe it sounds like the idle air slide is working ok (the thing below the air intake tracts, just in front of the starter.
THe warmed up idle does seem a little low but a couple of things to check and possibly twiddle....

1... RPM actually that low? Check with an independent rpm meter
2... Does the charging light come on or flickering, especially when the lights etc are on? If so then you need to bring the warm idle revs up a touch
3... You could try and adjust the throttle stop screw on the throttle body to bring the revs up a tad, but do it when its warmed up.
4... Let it cool down and see what the revs are like when starting from cold.

I guess I would be tempted to leave it alone especially after checking point 2
HTH
Malc
 
Thanks Malc. The charging light does not flicker - but that assumes the light is working. I don't think I've ever seen any light come on except the oil pressure light at startup.

It is tempting to leave it alone since everything else is ok. I'll try to find a second measure of engine speed to verify the gauge.
 
Hi Tyler,

like Malc says the first thing is to check the actual idle. If it is as it says then id be inclined to adjust it as the cold idle does seem slightly low and as such there might be a need to undo the big idle adjustment screw.

Where in London are you? I love inka.

Regards,

Rohan
 
Hi Rohan - Thanks. Based on your's and Malc's feedback, it doesn't seem that anything is seriously wrong - which is always comforting!

I'm in the Camden/Primrose Hill area of NW London.
 
If you want to raise the idle, don't adjust it with the throttle stop screw. You need to adjust the idle using the idle air bypass screw on the bottom of the thottle body. Its about the size of a dime with a big slot in it for a screwdriver. More air = higher idle.
 
Andy - wouldn't I only adjust the air bypass to increase the cold idle? I thought the bypass closed once the engine warmed up, therefore in my case it wouldn't increase my warm idle.
 
No -- they're two different things. The cold air idle valve -- or whatever its called -- is the slider temp thingy located on the left side (drivers side over here) under the manifold. That's controlled by the coolant temp and doesn't have an adjustment that I'm aware of.

The idle bypass screw I'm referring to is on the right side of the motor, just under the throttle body -- its a little hard to see with all the hoses in the way. Its a brass colored screw with a relatively big, flat head and a spring under it. This opens or closes a small air passage to let a limited amount of air through when the throttle plate is closed. The amount of air is the same whether its hot or cold -- but be sure to adjust it when fully warm so the cold air valve is fully open and doesn't throw the adjustment off.
 
Thanks Andy - out of technical curiousity, why is adjusting the air bypass screw better than using the idle stop screw?
 
If you look in the factory blue books, the thottle stop screw has a very specific adjustment procedure to get it just right. The throttle shaft has a cam and lever under the big metal cover which dictates when and how quickly the throttle position sensor turns. So unlike a carb, cracking open the throttle plate slightly to allow in more air also messes up the throttle sensor adjustment and changes how it opens. You should really set the stop screw by the book, then leave it alone and make all of the idle adjustments with the bypass screw.

Hope that helps!
 
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