High Idle

[n/a]

Hi,

I have a 1966 230sl with a 250sl engine and here is my problem.  I can't get the idle at the proper speed.  I have done the linkage adjustment according to George's instructions.   When you use the idle air adjustment to get best idle, it at around 1500-2000 RPM.  I then went to the idle fuel adjustment on the ejection pump and turned it CCW a few clicks, no effect on idle.  I did this procedure until the idle fuel adjustment screw was so far out it was causing the adjustment knob to rotate when the engine was running.  I corrected this by turning the adjustment CW back to the original position.  I went past this turning CW and still no effect on idle speed.  I made sure the cold start valve was not leaking by disconnecting the fuel line.   Any thoughts?

Doug Goins

[Naj ✝︎]

Doug,
To reduce idle mixture fuel, you need to turn the fuel screw CW.
Are you sure the cold start air supply shuts off completely when the is warm up enough? This is the air supply thru the small air filter on the inj. pump ( and piped to the bottom of the cold start valve).
When you start a cold engine you can hear the air hissing around this little filter and also feel the air flow with your finger. As the engine warms up, the hissing becomes less audible and then completely shuts off.
naj

65 230SL
68 280SL

[jakl]

Hi Rainman66,  just a thought - do you have the correct distributor for your engine?  That's the cause of my fast idle (1200 rpm).  Good luck.
-jakl

[Cees Klumper]

I am pretty sure that turning the idle screw on the FI pump counter-clockwise (CCW) makes the mixture leaner. This should have an effect on the idle. Are you sure you pushed the screw in far enough to properly engage the slotted screw behind it (engine off!)? You should really have a CO meter or another means of checking the CO value in the mixture when adjusting this screw. One method is by disengaging the linkages and independently moving the air intake butterfly and the FI pump to see how the engine reacts - Joe Alexander posted this method some time ago here.
Are you sure the air intake venturi flap is almost binding at idle? And that both the FI pump and the venturi are against their stops at idle? Turning the screw on my intake manifold has a very profound effect on my idle. Maybe the vacuum line to the distributor is loose / leaking ? This has an effect on the idle as well. Also check for other air leaks in the intake manifold. Is the (valve in the) hose to the power brake booster functioning properly? Finally, the ignition timing affects the idle speed.

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[n/a]

I got the following from a post by George Davis;

The idle fuel adjuster engages a slot inside the pump when it’s pushed in; when it’s not engaged in the slot, it simply spins free.
To increase the idle fuel, turn the adjuster clockwise, as if you were facing forward.
To decrease the idle fuel, turn the adjuster counter-clockwise.

If I'm standing beside the car on the left side facing forward then turning the know to the right would CW and to the left CCW.  Given this, which way should it be rotated to decrease fuel?


Doug Goins

[Cees Klumper]

To the left - CCW!

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[Naj ✝︎]

Doug,
looks like I've got the CW/CCW thing wrong  :evil:
naj

65 230SL
68 280SL

[ja17]

Hello Doug,
Make sure that the flap in the intake venturi is closing completely. Often times the 10mm locknut and adjustment screw is mistakingly used for idle adjustment. This is a factory setting and it should be set so that the flap in the venturi closes completely and just barely does not bind. If this is not adjusted correctly the engine will never idle correctly.

Joe Alexander
Blacklick, Ohio

[Ben]

One other thing I would do, having ensured the linkages are set correctly and the timing, is to screw in the idle air screw on the inlet manifold. If you keep screwing it in the engine should stall. If not then you have an air/vacuum leak somewhere on the inlet manifold. This could be at any of the threaded screws, the brake booster pipe, the vacuum advance line or anywahere else there is a joint.!

Regards,
Ben in Ireland.
'64 230SL 4sp.
'03 CLK Kompressor