Maurice - Nothing is as it seems. I just checked my car AGAIN. Here is something new I found.

1. Start car - runs a bit rough (A/C off, gear in P), around 650 rpms or so.
2. Put in gear. Rpms drop to 550 or so. Car runs smooth - perfect.
3. Turn on AC. Rpms don't change. Still smooth.
4. Turn off AC. Rpms don't change. Still smooth.
5. Put the gear back into P. rpms go to 1100 or so. Rough. They don't go back down until I put it back in gear. When I do, it's smooth again.

In the manual they attribute a high rpm usually to the air intake valve - the part I just futzed with. But would I then not also have a problem in gear? And why do the rpms stay in spec when the car is in P after starting, but go out of whack when I shift back into P after having been in grear? Could it be a bad switch somewhere?

On your car, the valve cover gasket - has the "C" modification been done to your heads? Mercedes came out with a set of instructions on how to modify the gasket surface of the heads afer they changed the material of the replacement valve cover gaskets. You need to deburr the heads around the area of the fuel injector seal holders. This is not in the CD ROM or manual - I found it on ALLDATADIY.com. It's a Benz technical service bulletin. Here is how the text reads:

As of May 1991 production, the above mentioned engines are
equipped with valve cover gaskets made from a new material.

In case of repair of engines prior to production phase-in, install only the modified valve cover gaskets. To avoid later leaks, the respective cylinder head must be reworked prior to installation of the gasket in engines 116.96/117.96. The procedure is described in this bulletin.

1. Remove install injection valves and insulating sleeves.
2. Close off bores (A) completely, e.g., with paper and carefully cover valve train as well as air flow sensor (Figure 1).
3. Remove any burrs surrounding injection valve bores (A) (i.e. using a hand grinder) (Figure 1).
4. Hone gasket joint face (arrows) with emory cloth/sand paper (100 - 180 grit) or oil stone to remove any shavings, especially in the area around the bores (A, Figure 1).
5. Mark reworked cylinder head with the letter "C" (Figures 2 and 3).

There are a whole bunch of diagrams - I recommend you go look it up. I have not found the "C" on my heads yet, so I refuse to remove the valve cover gasket until I am ready to do this...

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

Henry - check the piston in the idle valve and make sure it is not sticking - if it is sticking it can cause the problem. Look into the bore of the valve with a bright light and see if there is any crud residual in the bore that could be causing the valve to hang up. Don't think you have a major problem here. Don't forget the sensors on this car cause different things to happen when engine is in park, drive, ac on - off etc - if the motion of the valve required by sensors does not happen idle will be affected. To see what I mean - pull the electrical connector off the idle valve and watch the revs pick up. OR - just drive the car for a few days and see if the valve frees itself up - if it worked once - it should again. In fact - after you put the filter in - I'd just drive the car for a few days and let the dust settle - then look at the idle at that time - easier and won't hurt anything!
This head mod you mention - the seal is good all the way around the valve cover except at the outer rear corner of the valve cover - the oil leak is very small - just a drop or two in a minute - but enough to cause smoke and smell - when I turn left the oil is pushed up against the outer part of the valve cover and the rear corner starts it's little drip - Do you think this mod around the injectors will cause the leak at the outer rear??
thanks

Maurice -

Don't know why it would leak there. Unless the leak is where they described the work should be done, and for some reason it travels along the side until it drips where you see it.

A valve cover leak should not be that hard to fix, unless something is bent (like the cover), or you have a marr on the head surface. Some manufacturers don't even provide you with a gasket - they expect you to simply create a silicone bead and then bolt the thing down over it. Maybe you should try a new cover gasket with a layer of silicone sealant?

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

Hi Henry - tell me about it - valve cover leaks are easy - right? I have just rebuilt a Vw Turbo Diesel and I maintain all my cars - but this stupid little gremlin is driving me nuts. The only thing I can see is that the valve cover just covers the head to the edge - there is no piece of head extending past the valve cover gasket. The rubber valve cover gasket pushes onto the bottom of the valve cover and goes up the side of the cover by about 1/2" both inside and out for a good seal. The sealing surface of the gasket is flat and about 3/8" wide. On the aftermarket one there is a round rubber bead about the height of a pencil lead molded into the bottom face of the gasket and about 1/16" in from the outer edge. If this bead is not grabbing the back of the head - I believe that is causing the drip. That is why I am trying to find out if a Mercedes gasket has another molded bead 1/16" from the INSIDE of the bottom of the gasket - as if it did - it would definately seal for sure. Like I said - a stupid problem. I don't want to use silicone unless it is absolutely necessary. The car was designed to work without silcone on the valve cover gasket - and by gum - it WILL work without silicone - or I will die trying!! The problem of being a purist!!!

I know the purist problem. I'd also use silicone only as a last resort.

On my idle problem earlier - Actually the fact that the symptoms are changing means I am getting closer and closer to the real cause. For example, the fact that it is now rough when in Park, AC off, warmed up (same missing sound as before), regardless of RPMs, and smoothes out when I am in drive, rules out a bad fuel supply (we'd be even rougher at the lower rpms, but it's perfect there). The idle air valve should not be affecting this. However, a dirty idle air valve could have skewed the entire system enough to mask the underlying causes. I think in my case it was a number of problems, and they are not all resolved yet. But I feel more and more certain it could be a bad throttle idle actuator switch (there is a technical service bulletin out - it causes irratic idle rpms) or actually a bad transmission/reverse light switch. The latter seems to make the most sense - I sometimes get a strange hesitation when I restart the car and put it into gear, only when warm, only occasionally, and only for a split second. The tranny engages right away, but the engine seems to lose power for a second or two. I interpret that as the engine having a slow time realizing it's in drive.

The fun thing is now I am begining to narrow it down, and the diagrams are beginnig to be of use....

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

Now you have hit something I didn't know about. - Where is this throttle actuator switch???
Thanks - I will change mine on principle.
Maurice

Maurice -

Sorry - I did not use the right name - it's the idle contact of the throttle valve switch. In the manual diagram it would be S29/2. However, the TSB only refers to the 1986 model.

Anyhow, since mine is not rough right now when I am at a red light, I'll wait a bit before I tackle this. Who knows - maybe it'll settle down.

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

Maurice,

Got ahold of a fuel filter that looks just right today. Cost a whole $3.75 US. This afternoon I'll depressurize the line, use my trusty garden pruners to just cut the rubber line in half, and put on the filter. Wish it were glass so I could see what's going on inside, but oh well....

This weekend I am taking the car on a 600-mile trip. This should give the cleaners I put in the fuel and the oil a good workout...

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

Hi Henry - at the end of your journey I will wager that your problem will be gone! Just wish I had thought of the filter before I changed my fuel lines - would have been a lot cheaper and a lot less hassle!! By the way - on a different topic - how are your door handles? Light faded gray that makes your car look old? Don't Laugh at what I am going to tell you - my wife did -but it works!! I read on this site last year that guys were putting peanut butter on their handles and rubbing it in and letting it sit awhile before rubbing it off and it brought the handles back to the nice dark gray they should be. Well - with my wife laughing her head off - I smeared peanut butter on my handles. Let me tell you - it has been 2 months and they still look new!!! Sometimes the stupidest simplist things work best! If you do it - do it in private or be prepared to be the butt of many jokes

Maurice - do I sense a hint of Candian mischieviousness???


Actually - my look new and grey. But I did not use peanut butter.

I used a black trim restorer. Also works on tires. Really works.

Maybe it's made of peanut butter?

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

Henry - I swear - it really worked!!! I tried Armorall and other such products - but 2-3 weeks later they were dull again - laugh if you want - but it really did work!! When I want to be mischievious I go to an auto parts store and ask for a thermostat for a 1974 VW beetle (they are of course air cooled!!!)

Maurice -

Ever noticed that the plastic bottles some peanut butter comes in get really waxy and sticky on the outside over time? It must have something to do with the peanut butter oil and its reaction with the plastic - the plastic must be absorbing it. Even happens when the peanut butter is in the refrigirator.

So I don't doubt it works. Maybe even just pure peanut oil works. Interesting....

Hey, we could manufactur a "patented compount" that restores all of your under the hood rubber, and really just be selling peanut buttern in an aerosol can! :p

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

We'd never get rich doing that - Let's patent the peanut butter and sell it as a mud pack to restore suppleness to skin!! Added bonus - you can snack as you pack!!!

Maurice -

The fuel filter is in. No leaks. Let's see how she holds up.

I think it was more preventative than anything, because I do think it could be more related to a switch or sensor at this point. Otherwise she'd be rough in "D" with the AC on - now she is only rough when warm and in "P" or "N".

I ordered the special diagnostic cable you can put on the various components, such as the idle air valve. It was US$ 28 something or another from Samstag Sales. I thought it might be a worthwhile investment for diagnosing components and working along the diagnostic flowchart using a multimeter. Being German and actually from the town the car was built in, I have this thing about following the book...

But all this can wait, because at least she now behaves when I'm at a red traffic light, and I am really beginning to enjoy the car.

I am now busy botteling peanut butter into spraycans....

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

Let me know how she runs after your trip this week end - Let's keep the fingers x'ed - BTW - will the spray cans be available in smooth and crunchy??? :p