Hi,

I don’t know anything about these cars first of all but I cannot help wanting to comment about the vacuum lines either.
My 240’s use vacuum to do similar tasks but simpler.

You stated that you checked the “turbo boost systems vacuum lines.”

I think you need to forget that turbo stuff for now.
It seems to me a surge in idling has nothing to do with the boost responses or any pressure sensor.
The turbo is dead until it gets exhaust gasses to spin it.
As far as the computer goes it has finite perimeters to follow to control the turbo.

That system probably relies on a computer inputs like the RPMs and type load present from the transmission sensors.
It calculates the needed amounts of idle air or boost depending on what gear the transmission is in and the throttle position from the driver.
The throttle position is about the only other input that comes from the driver.
No CEL means nothing emissions wise is out of line far enough.
Excessive idle speed isn’t watched in the codes as its a naturally man made variable.

The vacuum lines that the other posters are recommending for you to check out are probably everywhere else on the car.
I suggest that you isolate different parts of those areas that use vacuum.
Figure in the cabin vent or heating controls, any line going down to the transmission or over to the power brake booster.
Especially, if it’s warming up with a foot on the brakes.
Common place to happen on a car that not dependably smooth.
Hopefully it’s not bad enough to cause the cell phone to jump out.🙄

The engine is the vacuum source and you work out from there towards any branches until something changes.
It’s not all that hard to pinch off lines but keeping your methods simple take practice.
This helps to narrow things down to an area and how it’s getting more air to allow the engine to rev up in the first place.

The scientific way is to one thing at a time and look for results and keep working outwardly to find a defective line or component.
Something is not working proper or is trying to correct another thing that isn’t.
A misfire on a cylinder will cause minimal idle fluctuations but a leaner condition from excessive air mimics other problems.

How long since an ignition tuneup?
You haven’t been on the BRICKBOARD if the last seen is right on the first post.
The engine is getting air it’s not supposed too.

Suggest you to Use the KISS method as much as possible.
KEEP IT SIMPLE STUPID.

There should be a vacuum routing diagram on the car underneath the hood on newer cars along with other labels. That is, unless the rules have changed and they do not disclose that information to make you buy manuals or to get the car serviced.

AS I mentioned earlier, the main input to any computer is the drivers foot.
In being such an item that uses a variable scale throttle control to talk to a computer. They have thin internals that wear out the faster or are more susceptible to getting fouled up by grunge or engine cleaners.
I don’t know what a Throttle Control Module is but if that’s your problem you don’t want that specific OEM one again.
The module name is fancier for more dollars.

I see from your dollar signs sprinkled here and there it’s big worry’s.
If I were you I would always request my old part, before leaving. I don’t know I’m that way but now in California it’s a law if you request them you better get them.
Just don’t mention it right up front because they have to find the problem and then produce the bad part.
If I was spending big bucks on service I would mark my cars components in an inconspicuous way.
By marking a part with a tiny scratch of a file, dab of paint or a inconspicuous ding with a center punch.
The BRICKBOARD is full of guys that take old parts apart to see what failed and how they work!
There’s one last thing, that the part can do for you, teach you something.

If you think I’m kidding then you haven’t taken a fuel injection in a city college several years ago.
The town’s mechanics talked shop during class breaks about how they get spare testing parts.
They hide them in their super size tool boxes.
It helps them to beat down the service times given to do a certain task.
There’s one to read the codes or do diagnostics with a machine for a print out but when they have already seen the symptoms before ….guess?
The customers never knows the difference if it was something simple that they cannot technically charge for.
So, they get a used spare testing part.
Customers car is fixed, dealer is happy and the rumble continues.
Mercedes were the most mentioned at that time for guess what, idle control boards. Now called modules.as
These varied from model to model so mechanics do what they do.
Advertisements then said, “Built like no other car in the world”. I believe they meant it too!

I changed out one on a 2002 Dodge truck for having excessive idle speed problems, that were MOST noticeable, when the vehicle engine was not loaded by the transmission.
I tracked it down by “noticing” that it would always hesitate to idle correctly or the same right after every adjustment with my foot.
The truck had a tachometer.

A new throttle sensor was $35 to $85. One being an economy one and the other was OEM.
Both were offered from the same parts house.
The decision was simple for me to get the economy one because we already had the OEM one that was failing.
An ohmmeter test helped as I remember but replacement was the final step but I tossed it after I took it apart!

It’s been about fifteen years now and the problem has not reoccured.
But then again that truck doesn’t get used as much.
My sister-in-law’s husband passed shorty before this and due to gas prices being what they are now, it sits on her place waiting to move something.
I ask occasionally and she runs it every few weeks and it’s still doing good. I figure it’s debugged!

Older vehicles still can be tougher and cheaper to maintain. Because 2000 vehicles were watching out for the “Y2K” issues that didn’t appear as much as the worriers predicted.
Manufacturers slowed down on the electronic gizmos.
But now,
For the last few years, that has “chipped” them in the butt!


Hope this gets your hands and mind into the car more often.
It’s been awhile since you worked on it. A January thread?
Hopefully others with more experience on this series can chime in.


Phil