On euro 83 500SL...

Label on engine says 16 degrees BTDC @600-750rpm, and 25 degrees at 2500rpm.

History: New rotor/cap, chain/guides, intake manifold gaskets/plenum gaskets, New injectors/seals/insulators before the manifold job. Car idled relatively smoother before, but rough now. Plugs were Champions before the repair, changed to Bosch W7DC's with pre-gap of 0.32". Possibly mixture, but I have a potential vacuum leak problem that is bugging me (see below)

I timed it with vacuum attached to distributor advance for above reading at idle, car seems to have lost some 'zip' and idles rough. Did I do it wrong? Have not adjusted mixture controller at all (yet!)

Do I time it with vacuum connected or disconnected? When I disconnect vacuum the timing mark shows '0'/TDC at idle, is this correct? With vacuum connected, shows 16 degrees at idle, and then goes way up to 30-35 before 2500rpm which is way too high imho.

Also, I suspect I may have vacuum loss somewhere, the vacuum gauge floats off about 1/6 at 750rpm, is this normal or should it be PEGGED shut?

You are correct, it is 16 degrees with the vacuum attached. You are too high at 2500 rpm, probably because I think you do have a vacuum leak somewhere or an egr problem. You really need to find the cause of the rough idle before going further.

You could try to adjust the controller some and see if it smooths out any but you could be compensating for a leak by setting it rich, CW richens, CCW leans. Don't know if you tried it yet but the ol propane torch trick might help you out. I would try running it around the intake/plenum gaskets to see if it sucking air anywhere. If nothing shows there, try all the vacuum fittings. If there is a leak, the engine will speed up when it sucks in the LP.

Since the car run okay before all the gasket changes why did you put in new intake/plenum gaskets? Have you pulled the plugs out to see if there are any abnormal burning signs?

If you have O2 sensors on it, you could hood a multimeter to one of them and check the voltage, should be around .45 to .5 volts if your mixture is set right. .42 it supposed to be perfect but it is a little lean on the low end for performance. I had to lean mine out for emissions testing then set it back to around .52 volts.

The only other thing I can think of, and this is one of those IMHO deals, you might want to change the plugs to a copper based plug, I use NGKs. There are continuous opinions about the platinum plugs not working well on the older MBs


Frustrating....

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I really gets fun when they all don't run

84 500SL
99 Jeep XJ
93 Jeep YJ
03 Custom Softail

I did the propane test and it appears theres a leakage around the #3 cylinder (the one behind #1), either around the fuel injector or the manifold gasket itself.

The gaskets are new, and when I spray propane or carb cleaner I do see a change in engine speed. Thus, assuming there is a leakage, I need to retorque the manifold bolts. All of them were torqued up to 20 ft lbs, I got this from another member, but this MIGHT have been for the 450 iron block. DO I need to torque them to higher specs, i.e. 20 Nm?

Assuming one injector seal/insulator leaks, would that really affect system vacuum that much?

Im hoping that is the case here, a retorquing of the manifold.

Vacuum gauage is SUPPOSED to stay pegged throughout the idle range, correct??