OK, here is the mystery:

1964 230sl, fully sorted-out except for idle problem. Car starts fine, runs fine, warm or cold, idles at 900 cold, 700 warm (10-20 minutes around town driving) but if I take it up to high temp., i.e. run it at highway speed for 10 minutes or around town for 20 minutes, especially on a hot day, idle goes to 1000-1200. Adjusting the idle back to 750 in hot conditions makes it undriveable (idles at 400) when back to warm. Any guesses? And thanks for your response,

g

Next tme it does it, remove the ball link at the throttle plate and push the throttle plate closed ..see what happens ..try to do this without any other links moving [ ie , the IP pump link]..

My first view of those FI cars was to verify the action and stability of the thermostatic warm-up control. Ilde air speed is controlled by adding air through the idle air screw. There are two other sources of air: the closed throttle plate and the auxlilary air valve. This valve is under the thermostat in the injection pump.

The thermostat pushes the airslide closed as it warms up. It changes mixture at the same time. A properly working device with be fully shut at probaly 140-150 degs. It has to be shut before operating temp as one doesn't want a varying mixture or air source while in operating temp.

To test pull the airfilter off the thermostat (on back of injection pump) and plug the hole with a thumb. When cold this will kill the car. When warm it should not alter the engine speed by more than 50 rpms. One will still feel suction but the change in rpm is the test. One should reach the final state of this valve before operating temp.

Timing also can change the idle speed a lot. Verify that there is minimal centrifugal advance in the idle speed range. If centrifugal advance occurs at 1000rpms the advance with take you a few hundred rpm higher as it advances.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

The sticky throttle plate at high temp is a common problem on the early 113.042 .. These had standard advance , where the later [ and all other 113s ] had vac retard. This should ,as SB said, be checked as it may not be coming back to idle timing. An easy way to check is w/strobe light , but you can also disconnect the vac hose and listen for rpm change.
I can tell you exact specs if you list the dist #.
Here is more info on the basics of these Mechanical Injection systems..
It is also advisable to check the dip stick at the rear of your pump for oil level.. the early pump had an oil res that must be owner checked/filled . These never get checked and will effect operation.

http://www.sl113.org/forums/topic.asp?TOPIC_ID=2257&SearchTerms=air,bleed,rich

This refered to site postings have to be read from the bottom to top for sequence for some reason, so start at end..

First of all, thank you guys for the thoughtful advice. I will try to diagnose one at a time tomorrow and let you know what works. I know already that the throttle body has some chaffing (very minor wear) inside where the butterfly meets the body in the closed position. May be a source of leak. Also, this is a very early 230sl but it has both vacuum and centrifugal advance (and electronic ignition...which I installed without effect on this current idle problem). As for the oil level in the pump, I watch it closely as this early model does not have auto-fill. What a pain it is to check, though. I never knew there was an air filter in the air intake for the pump, does this require maintenance?

Now, can someone just get me a get out of jail card if I work on this tomorrow...it is my wife's birthday.

Thanks all,

g
'64 230sl (my reliable car)
'94 E500 (my airport car)
'98 E320 wagon (wife's dog bus)
'04 C240 wagon (kids safety machine)

Found the problem, thanks for the advice. It was poor adjustment of the throttle valve actuator. One turn of the connecting rod was all it took. I think that the problem was very apparent on a hot engine as the heat from the manifold caused the rod to lengthen by enough to exacerbate the idle problem. Did not believe how sensitive this is, but that's what you get with MB...remarkable tolerances that need to be just right.

Really appreciate your advice,

g

__________________
64 230sl, my daily driver
94 E500, sold
98 E320, family and dog hauler
04 C240, safe machine for teen drivers, but a poc
08 audi a4, yes we have gone to the dark side

G,
Do not understand fine adjustment of throttle valve actuator. If you are talking about the solenoid on top of the intake, there is no fine adjustment for manifold heat. I believe you have an automatic and are referring to the solenoid that increases idle in gear. I suggest you check the throttle blade clearance. You can do this by removing the air cleaner hose, sliding a cigarette pack wrapper between the blade and housing, and adjusting the screw until it slides through with little resistance. Although the protractor sets are no lomger available, but you can still set basic linkage by lining up the hole in the intake manifold with the one bell crank on the cross bar facing that direction. Secure the cross bar in this position and adjust all rods to fit tension free. To answer your question, if you can't blow through that filter with no resistance, it needs to be replaced. I'll bet yours is plugged solid. Start crying now when you check the price of one of those puppies.

Peter

__________________
Auto Zentral Ltd.

Peter,

Man, you guys are good. Thanks for your post, but I think I led you down the worng path with my inability to accurately name these parts, so let me try again.

I first checked the usual suspects: the air intake on the cold start valve is fine, the actuator inside that mechanism works fine (I tested using the method in recommended in the prior post: after removing the air filter, there is strong suction with engine running cold, very light suction when running warm and blocking off this intake has no effect on RPMs of warm running engine). Also rechecked timing and vacuum advance, all good.

Now for the answer: The throttle blade (what I called the butterfly valve, but what the heck, I am old enough to know how to work on real carbs) was fully closed under cold and warm running conditions. But there was ZERO play in the connecting rod (what I called the actuator). But with hot car, the connecting rod located directly above the hottest part of the car (even with properly installed manifold shield) the rod actually lengthens enough--all it took was .003 inches or so (I believe that's about the width of the cigarette wrapper you mention) -- to push open the throttle blade and cause the raised idle. And the hotter the engine, the longer the rod, the wider the gap and the higher the idle. Accounted for a maximum increase of up to 500 RPMs.

Now that no one is still with me, let me go on. Did you ever see the glass tubes of mercury in a pendulum of an antique clock with a metal pendulum rod? They are not there for show. They are there to keep the moment of the pendulum constant: As ambient temperature rises, the mercury rises in the tubes, and thereby offsets the effect of the temperature on the LENGTHENING OF THE PENDULUM ROD. Longer pendulum makes "center of gravity" (moment lower) which would otherwise slow the clock. But this is offset by the rise in mercury that puts more weight toward the top of the pendulum. Yep, its true.

Thanks,
g

__________________
64 230sl, my daily driver
94 E500, sold
98 E320, family and dog hauler
04 C240, safe machine for teen drivers, but a poc
08 audi a4, yes we have gone to the dark side

G,
I believe you on the mercury. I am somewhat familiar with early clocks. I know that one of the drawbacks of the verge and folliet (sp) design was the uneven unwinding of the spring until carbon steel was discovered, but believe me the tollerences are not quite that critical on an MB.

Peter

__________________
Auto Zentral Ltd.

Autozen, you are spot-on with your comment on tolerances. I was just suggesting that I was so close to the release point that absolutely any pressure would cause the valve to open, and that the pressure could have come from any lengthening of the rod, in this case via microexpansion from the manifold heat. Probably could not repeat this condition in a million tries. Backing it off one turn, in any case, solved the problem, which is what I was trying to accomplish!

As the Mad Hatter said: "If you don't know where you're going, any road will get you there."

I really appreciate your advice and your posts, my sincere thanks.

BTW, you are also correct re: carbon steel and it's contribution to horological accuracy. For a facinating look at this and other issues regarding the pursuit of zero-variation in timekeeping, a great book is Longitude, please see:

The Story of Longitude by Louise Borden,Erik Blegvad.

And thanks again.

g

__________________
64 230sl, my daily driver
94 E500, sold
98 E320, family and dog hauler
04 C240, safe machine for teen drivers, but a poc
08 audi a4, yes we have gone to the dark side