Recently I've been having the Hot restart troubles followed by the "here it comes again.." miss & rough Idle on my 1987 300SE Euro. I again did a lot of reading , a few tests of my own and consulted my Mechanic. Here is what happened and what I did.
Following a fuel pressure test and getting stuck in a major intersection in town, I replaced the fuel pump (4 yrs old only!) and filter (was 1yr old- but since I was already there...) I actually thought this was very early for a fuel pump to fail, but learned of other cases where that had occurred. This action seemed to cure the hot restart - Not completely though. The accumulator was replaced too, a year ago, so for good measure and thinking of possible leaking injectors, I replaced the injector seals (7 yrs. old) and the Spark Plugs that had only 20K on them but looked bad. On the other hand, The rotor&cap as well as the plug wires only had about 30k(4yrs) on them so I was sure I was OK there-

In the few weeks this was all taking place the rough Idle/Miss issue was developing rapidly. I checked the Idle valve & hoses. They were good. I removed the fuel pump relay and bridged it just to make sure the relay had not gone south.- The miss was still there, so I deducted the relay was good. The OVP fuses were good, nor did the OVP exhibit any of the other signs of going bad (the check engine light, the ABS light etc )
I then noticed the #1 plug was fouling quickly so I replaced that injector with an old one I had to see if indeed the Injector - rather than it's seal was leaking. This was getting very frustrating - Yet all the stuff I had mentioned above as changing was good maintenance, even if a little premature.
The #1 plug was still fouled , so I thought of one last move before facing unknowns like a coil, which I did not think it was, or the big ticket items which I cannot diagnose myself like the distributer or the Idle control computer.
My last move was to go ahead and check the Cap & Rotor anyhow. That lower hard to get to bolt, plus the knowledge that "on paper" they should be good, made me shy away from digging in there. Well to my great surprise and relief- there it was...Victory at last. All torn apart inside !!!!
I am not sure why, but the Distributer Cap is worn out unevenly . The #1 slot is completely gone !! I thought it would wear out evenly. So something is out of balance. What does this indicate about the engine if anything ?

Check out this thread for possible problem/solution.


A good, tough problem- 300e occassional stall after warm-up

Hope this helps.

Brgds,

BENZSTER

BENSTER, Thanks for the suggestion and links. - I was away from home & car for a week, and now is the time to continue this exploration.
The first thing I checked (before installing new Cap & Rotor) was the Aluminum Rotor driver for any slop - there just is no play there . It is firmly in place . I thought I would wait a few weeks and then dismantle the Cap & Rotor again to look at how evenly it is wearing.
BUT this did not cure all things and should remind me yet again NOT to write about a fix before some real time goes by...

The good news - After replacing the fuel pump & filter plus the distributer cap & rotor, I also swapped the spark plugs(twice) and replaced the Injector seals.
All this seems to have pretty much taken care of both the cold & hot restart. The Idle is much better .

The bad news - When engine warms up there is still a slight miss at Idle. At times I can hear it hunting - Also the spark plugs foul up bad very very quickly. So I think I might have a very Rich mixture or not enough Air.
To add to the problem, the #1 plug is also wet. I did swap that #1 injector a couple times - The plug is still wet. From readings here on the forum this might indicate bad valve stem seals. However once accelerating above 1500 RPM the miss cannot be felt and the car rides very well. There is neither noticeable loss of oil nor fumes or smoke out of the tail pipe. Last thing I notice is that the Idle actually drops quite low when placed in gear. Is this correct or even related ?

1987 300SE Euro 126/103

When was the last time your valve stem seals were replaced?

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

What are the plugs soaked with? Oil or fuel?

Have you set the pressures in the distributor properly?

How much vacuum are you pulling at idle?

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

It could be the drive gear of the distributor, or a bearing gone south in the distributor housing. That is about the only two things that cause the rotor to wear the posts unevenly, (not from spark, but from friction from the rotor being spun in an ellipse instead of a circle.) Worn bearings cause a wobble (ellipse) rotation of the rotor.

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1986 Euro 500SEC "RUF" 9:1CR, "Rose"
1985 Euro 500SEC Cabriolet AMG Widebody
1982 Euro 500SEL "Blue"
2001 Texas Heeler (Aussie/Queensland X) "Sulphie",
2012 Queensland Red Heeler "Squeak"
Best dogs I've ever had.

ps2cho, thanks for the input. Your comment and my thought on the Valve Stem Seals are addressed below.

Jonathan1-I went back and checked- The Valve Stem Seals were replaced about 50k miles/5yrs ago.Should still be good, no? (no smoke, no loss of oil ). This car is a daily drive - mainly in city traffic, and not more than about 10k miles a year. So it has not been sitting about idly(ha ha) allowing rubber and seals a chance to dry out and crack.

HitmanX - the # 1 plug only is soaked with fuel, not oil & very sooty/ the other 5 just very sooty. I have not touched the distributer and have no vacuum gauge. I will try and borrow one - What should I be looking for at Idle ?

Chadahar- The rotor driver was solid with no slop as I had mentioned. I will look at an engine diagram to understand your comment better . This would not effect the "current condition" at the moment now would it?

1987 300SE Euro 126/103