High Idle RPM

[saygold]

I have a 1966 230SL with a 4-speed manual transmission.  It was running well until I tried to tweek it a little.  Now, the engine idles at about 1800 rpm, and I can't get it down.

Basic info:
European version
051 distributor
New points, cap, rotor, spark plugs and cables
At 1800 rpm, the dwell is 39 and the timing is at 12 BTDC with vacuum connected.
New vacuum tube installed- it was the purple colored from Mercedes Classics.  A suction/blow test indicated the diaghram was still intact.

FIP rack moves smoothly in both directions when using a threaded rod.

The linkage tour procedure was followed when getting the car running well with a 750 rpm.  The linkage rods have not been changed since the RPM problem occurred.

The fuses (in the engine panel box) were visibly inspected, with no problems seen.

I tried to tighten the bolts on the thermo time switch, and broke the insulation; I installed a replacement unit from Authentic Classics with the plug-on system.  A quick check showed the resistance to be 38 ohm (g) and 12 ohm (w) with the water temperature gauge showing 55 degrees C (using the dashboard water gauge).

I inspected/cleaned the CSV.  I cleaned the spray nozzle with a fine wire.  There was no fuel coming out of the inspection hole in the CSV when the fuel pump was on. 

I turned the FIP idle control valve CW to the end then 25 clicks CCW; the high rpm at idle continued.  An additional 10 clicks CCW (in two stages) did not change the high rpm idle point. 

What should I check next?

Thanks in advance for your assistance.

Best regards,

Ken
1966 230SL euro, 4-speed.

[kampala]

Try retarding the timing back a bit to about 8 BTDC.   

What's your timing at 3000 rpm?

[Tyler S]

I see no mention of the idle air screw  on the intake manifold (large slotted screw) being adjusted. You may need to go back and bring the idle down below 1000 with the air screw and then re-do your mixture adjustment on the FIP. If the idle is too high then adjustment of the FIP idle mixture screw will not do anything because the internal flyweights have taken over and in effect cancel out any idle settings.

[saygold]

Thanks for your comments Kampala and Tyler.  I reduced the air to the intake manifold and the fuel pump idle settings in stages and the car now idles at about 800 rpm.  However, when disconnecting the FIP connecting rod and the throttle rod from the control shaft and then opening the air venturi valve when the engine is running, the engine rpm increases up to the 1800 rpm range.  Looks like I am still at square one.

Does the intake starter solenoid shaft extend when the engine starts, then retreat when the timing has been set?  If so, and the intake starter valve is stuck with the fuel flow open, that might be at least a part of my problem.

Thanks

Ken
66 230SL Euro, 4-speed

 

[Tyler S]

You are still rich. Need to keep leaning out the injection pump thumb screw CCW a few more clicks until you find a balance.

Yes the cold start solenoid functions Only when the starter motor is engaged. If the valve is leaking internally it will cause a rich condition. You can remove the small 7mm cap bolt on the side of the valve. Make sure there is no fuel dripping out with the key on (not running).

[saygold]

Thanks for your response.  It appears that I am not able to use the adjustment knob effectively, so I ordered a 42mm wrench to open the cover of the low-rpm adjustment bolt.  I can the be sure the nut is turned.  I will have a small container to catch any oil built up inside the cover.  Any seals or O-rings required? 

Best regards,

[Tyler S]

No seals or o-rings.
Are you pushing in on the knob while turning it? You should be able to feel the detent engage and then be able to turn it with resistance felt. The other end of the knob looks like a flat bladed screw driver so it needs to be lined up correctly with the internal screw first before you will feel resistance and the "clicks".
You are performing these adjustments with the engine OFF!?

[ja17]

Hello,
Your 1970 Pagoda should have version 4 or version 5 of the  starting devices. In both cases the CSV on the intake manifold operates at engine temperatures below 95 degrees F.  It should not function at engine temperatures above that. As temperatures decrease, the actuating time increases. With version 4 starting devices, the injection pump starting solenoid operates when the starter is engaged. With version 5, there is no longer a starting solenoid on the injection pump.

[saygold]

Thanks for your comments, Tyler and Joe.  Yes, the engine is not running when turning the adjustment knob.  The knob rotates when pushing in the knob and turning, but the air/fuel ratio remains rich at idle.  I can feel the nut being turned the knob rotating shaft is not always properly aligned.  I will test it again today.

This is for a 1966 230SL with s/n of 16xxx.

[Tyler S]

Make sure the car is fully warmed up when testing/adjusting. If you cant get any change and you are near the max you can turn the knob ccw then you may want to start looking at adjusting the full range screw or removing shims from the Baro sensor. Assuming everything else is correct such as linkage, throttle plate, WRD function.

[saygold]

Thanks for all of your help.  I found the major problem: the throttle linkage rod from the pivot point on the right side of the engine going to the pivot point on the top of the intake manifold was rubbing against the asbestos heat shield between the intake and exhaust manifold.  I slipped the heat shield forward slightly and the high RPM at idle disappeared.  Should have looked closer again before I asked for help.  Now going through the timing, dwell and FIP idle setting and will test the car out tomorrow.

Best regards,
Ken