Slight surge coming to a stop. - PeachParts Mercedes-Benz Forum

96C280 · #1 02-02-2004, 01:54 PM

I have a 96 c280 in which I've recently noticed when I brake to a stop, the last moments before coming to a complete stop there is a very slight but definite pulsating (couple to 3 times maybe) or maintaining of the rpms before dropping to the final idle speed.

This occurs as during the 700 to 550 rpm range (or the last 100 or so rpms before idle.

Once it reaches the idle, there is no fluctuation of the idle and is very stable. I don't notice any other drivability problems.

The MAS was replaced a year ago when there was a an extremely erratic idle which cured that problem, but have only noticed this problem recently.

I've read some of the posts about vacuum problems but in trying to analyze the symptoms, it almost seems as if there is a delay in totally releasing the transmission as I come to a stop. Could it be a torque convertor situation? ATF level situation? Once at a complete stop, everything is normal, the usual MB creeping forward.

jlomon · #2 03-06-2005, 03:03 PM

*bump*

My 1994 C280 has just started to do this exact same thing. The idle surges, or pulses, between about 600rpm and 900rpm as I come to a stop. It only happens when the car is in drive. When I start the car and drive away, it will not exhibit the problem the first two or three times I come to a stop. Then it will surge for for three or four stops, then the idle becomes smooth again. There are no driveability problems at any other point in the RPM range and it does not happen in park.

Any ideas?

Jonathan

jlomon · #3 03-08-2005, 11:55 AM

I'm going to bump this again incase it got lost over the weekend. If anyone has any ideas on this, I'd really appreciate it. I've searched and found a few threads that have similar problems on M104s but nobody has posted what the solution was.

Many thanks,

Jonathan

Mike Murrell · #4 03-08-2005, 11:59 AM

What you do is go to the SEARCH facility and key in -> M104+surge, then click on "titles only". I get 2 hits.

http://www.peachparts.com/shopforum/search.php?searchid=229833

rsmcmahon · #5 03-08-2005, 03:43 PM

Does the inner lining of the Throddle body have a build up on the surface area? A carbon build up preventing the "butterfly" flap from closing properly can cause problems similar to what you are describing. I however only have experience with several m119 engines on the W140 and W124 models.

96C280 · #6 03-09-2005, 07:40 PM

I've come to the conclusion that it has something to do with the vacuum directly or indirectly involved with the transmission and perhaps the throttle position (adjustable with the slide and other bowden cable to the gas pedal). If I adjust the bowden cable to the trans (see below), I get varying levels of the surge to the point where I really don't get any surge. However, it's never completely gone as after a long drive where things have warmed up a bit, the first stop or so it will have that slight surge. My mom has a 94 c280 that is almost in mint condition and literally smells like new inside and drives tight like new. I use it as a benchmark when I fiddle around with my car. However, I noticed the last time (I think because I'm specifically looking for it) it also had a slight blight of the rpm as it comes to final stop. Of course all this means is that if the car wasn't adjusted then something has changed, i.e., car is aging but adjusting it can alleviate the situation. Throttle bodies of both cars are very clean.

Side note: which you might see in my other posts, adjusting the bowden cable, throttle linkage can literally make this car drive differently like night and day. Smooth takeoff, nice shifts, good midrange. It literally tunes the car (despite the MAF, electronics, etc.) Unfortunately the combinations are infinite and I have now been trying to get the elusive setting I had at one point which was really sweet, better than OE (honest to you know who). Of course, couldn't leave almost perfect alone. It's been like the holy grail. So if ANYONE has some official MB instructions on this for some insight I'd appreciate it.

mbdoc · #7 03-10-2005, 08:32 AM

Many of the 1996 cars with M104 engines did that from the start!

WHAT you are feeling is the de-cel shut-off system that turns injectors on/off so that the engine creates less smog!
ON many cars you can see the tach move 300-400 RPM as that takes place.
MB slightly modified the fuel computer so that shouldn't be felt!

terminator · #8 03-10-2005, 09:27 AM

Check brake booster vacuum line. I had the same problem and that was the last thing I checked. Turns out the check valve had a crack in it.

jlomon · #9 03-10-2005, 11:33 AM

Thank you everyone for your responses, I appreciate it. It looks like I need to spend some time tracking down a vaccum leak then.

MB Doc, if the issue you are suggesting is in fact what my car's problem is instead of a vaccum leak, then how would I go about resolving it? The car has never had this sort of an idle surge in the 5 years I've owned it. It is a 1994 model, not a 1996.

Thanks!

Jonathan

96C280 · #10 03-11-2005, 11:04 AM

Terminator, can you tell me where the brake booster line and check valve is? Thanks. I didn't mention in my reply but the brake and some kind of fuel feed/cutoff connection that M.B. Doc mentioned sounded like it would describe the condition. Is there some "connection" (not literally a physical one) between the brakes and the fuel cutoff function?