Engine hunts at idle

[jszeman1]

I have an early 63 230sl.
The car idles nicely when cold, but once fully warm the engine hunts up and down at idle. It will start to level out a little after a minute at idle but once you give it a blip on the gas it will start it idle hunt (from 750 to 1100) when trying to find the idle. It acts like it has a vacuum leak, but I can't seem to trace one.  If adjust the RPM's to around 1200 the engine runs smooth.

Any suggestions?

[Jonny B]

How do the brakes feel? My car had a vacuum leak in the booster that I chased around for way too many years. I could tell at start that there was something a bit loose with the brakes, but not anything that was ever a problem as far as stopping on the road. I think there are several strings on the forum regarding the booster vacuum leak you should be able to find. It finally took a new set of eyes on the problem to get it taken care of.

[jameshoward]

John,

I assume you've done and re-done (because it's an art not a science) the linkage tour that Joe has put on the site. With that ticked off, you may have a vacuum leak (brakes, etc), but it more simply it may be a case of needing to adjust the setting of the FI pump idle, using the small screw at the back of the pump. When I re-fitted my FI pump after some modifications, I found it had been leaned out (at my request). The car was running lean at idle and hunted. It took quite a bit of adjusting the idle screw on the pump and the idle screw at the butterfly to get the correct combination.

I'd suggest the lean running test, the procedure for which is on the site. It maybe that you're running lean and so a click or two of the idle screw may sort the problem. After a bit of faffing, my car idles perfectly at around 800rpm.

I'd suggest you start there.

[jszeman1]

Thanks for the suggestions.  The brake booster is OK, problem solved last year.  You might be right, my thought is that the pump is running lean at idle.  I will fiddle with it a little more.  Thanks