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

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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