I stand corrected - your cap does not have a spring-loaded center electrode!

I think replacing the bracket & bolt makes sense as this is what caused my problem. This is a pic of the bracket (althought the BMW variant):
http://data.bmrparts.com/bmwparts/7229690281594U.html

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89 300te 222,222
92 300e 190,000

btw, this is a thread where the guy was convinced his problem was with fuel system and it turned out to be an ignition problem:
http://www.peachparts.com/shopforum/showthread.php?t=62226&page=5&pp=15&highlight=duty+cycles

Since you can reliably reproduce the problem, I wonder if you could make an appointment with a mechanic within a ten minute drive and have them slap a scope on the ignition system, just to rule it out?

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89 300te 222,222
92 300e 190,000

Replaced the cap and rotor arm Sunday.

Had quite a fight undoing the three 3mm Allen key headed bolts that hold the rotor arm in place. They are made from grade 8.8 steel and were done up so tightly that my usual Allen Key just turned within the bolt's head rounding its edges. Eventually had to borrow a good quality Allen key and tap it in and round with a small hammer. Each screw gave a fairly load click/bang as it gave, also resulting with the washer on 2 of the 3 bolts fracturing as they were un-done.

Checked the back bracket held in place by the signal Torx bolt - all looked good so decided to leave it for now.

Had the car out for a long drive yesterday and it ran faultlessly (normally I'd have got at least a few hiccup in the idle). Have been using it a fair bit recently, but am back to my normal routine now, so car will be unused Wed->Sat this week. Main test will therefore be how it runs when I take it out Sunday.

Many thanks to all (especially Robert) for the help. Would have probably done the dizzy cap/rotor arm eventually, but certainly not before a period of further pain/expense - so many thanks for saving me!

Still cannot understand the logic behind the symptoms both Robert and I where getting and the (fingers crossed) actual solution.

Cheers,
Neil

So I was thinking this through and I think I have an explanation. When the mixture is rich there is less voltage required to create a spark (less resistance = less voltage). When the car is cold the computer makes the mixture richer. When the engine temp reaches 60C the computer changes the mixture to be leaner. I would speculate that this happens after about 10 minutes. So because our ignition systems are compromised by bad contacts in the distributor cap, the voltage couldn't overcome the resistance of a lean mixture and bad conduction in the cap. Not sure what happens when the engine reaches 80C and runs okay, but I would guess that the CPU makes it somehow richer or things expand in the cap and contacts are closer?

Robert

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89 300te 222,222
92 300e 190,000

I am not a Merc mechanic...and so most of what I read on this thread is WAY over my head. But, it was like I was reading a commentary on my car (92 300e). I have recently (last 2 weeks) had exact same problem. Stalls after about 10 minutes into my trip to work, 8 miles from home, in exact same turn (following fairly hard decelleration). Both times happened on a Monday after car sat all weekend. Shop first replaced few parts in ignition circuit (3 wires and all 6 plugs), but found nothing else in diagnostics. They are stumped without replacing parts in a most-to-least probable list.

So, was the final result of this thread a simple replacement of the distributor cap and rotor? If so, then I may point the shop into that replacement first.

They had suggested that it was most probably the Idle Control Valve, due to the fact that it happened upon deceleration both times. I am not so convinced since it appears that the more common issue seems to be sitting over the weekend, and being the same distance (mileage and time) from start-up. Otherwise, why wouldn't it have problems the rest of the week on deceleration?

Anyway, from a non-mechanical person like me, this thread seemed exactly like my issue.

What would you suggest trying first? Start with the cap and rotor?

Thanks for your input...

My problem was solved by replacing the cap, rotor, and rotor driver bolt. Many MB dealers consider the rotor driver to be a tune-up part. In case you're wondering, the rotor driver is a little bracket that lives behind the rotor and attaches the rotor to the camshaft. In my case the rotor driver bolt was broken. It seems odd to me since there is practically zero strain on this bolt, but apparently it's not totally unusual for it to break.

The prior owner of my car replaced tons of parts, including the computer before selling the car to me at a steep discount (and not informing me of the problem). Funny how a little bolt was the crux of the issue.

Robert

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89 300te 222,222
92 300e 190,000

Robert...thanks for the info. Like I said, I'm not able to repair much, but on most cars replacing the rotor, cap, bolt would be an easy task. Is it as easy on this car?

Thanks

It's Monday again. Car sat all weekend. Car stalled at EXACTLY the same spot (about 10 miles/10 mins from home).

Going to get the distributor cap, rotor, and bolt TODAY.

Hope this is an easy job!

Any tips for a novice?

As with Robert, my stalling problem does appear to be fixed by installing the new dizzy cap and rotor arm (note I didn't need/do a new driver bolt). My occassional idling 'hiccup' though is still there. I was hoping it was related to the stall but now looks to be a separate issue........

I'm no mechanic either, but the cap & arm are easy to do. Only tips/thought are: 1) The thing Robert mentioned to me about rotating the fan to find the place where the blades are wider than normal; 2) using a good quality hex socket set as the bolts are made from toughened steel and are done up pretty tight; 3) make sure you reconnect the leads securely and in the correct order.

Enjoy,
Neil

Recently my 300SE (W126) had a problem with misfiring and stalling after driving it for 5 minutes. After switching the engine off for 15 minutes it did run fine for the rest of the day.
Today changed the relatively new Beru cap, rotor and wires for original Bosch and put new plugs in. No more stalling and misfires. The Bosch wires are thicker and less flexible than the Beru wires.
Fortunately I could rule out fuel problem, since my car has gas and LPG.