W124 Idle Surging...I'm Getting Fed Up! - PeachParts Mercedes-Benz Forum

G-Benz · #1 01-06-2003, 10:14 PM

Fast surging when W124 is in gear (worse in reverse), slow rise and fall of idle speed when in park.

Did the searches, (variety of theories), checked the Haynes manual (little help), and even threw a few parts at the problem (temp sensor, air mass sensor $$$). Pulled and reattached vacuum lines all over the place without any diference in the engine's behavior (as far as the surging is concerned). Bad harness was replaced under goodwill three years ago.

This was my very first post over two years ago and although I have had great success with you guys in solving my other W124 issues, this one seems to remain.

Problem hasn't worsened, but it lingers and I'm growing weary of it. Thinking of throwing the towel and shelling out $$$ to let the dealership figure it out!

To add to that, engine stumbles at first when started cold. Will stall if put in gear before a short warmup.

I would like to keep this car out of the shop if at all possible. Need to know what series of components I should be attacking for an effective diagnosis of the problem.

Help! I gotta figure this out!!!

blackmercedes · #2 01-06-2003, 10:20 PM

Well, since you're so desperate, I'll throw my non-mechanic, non-tech-expert $0.02 in.

MAS, done! Harness, done! Sounds like the usual suspects are already in jail!

My 'ol 190E 2.3 did the same thing, and I had trouble solving it too. Turned out in my case that the seal where the tube thingy connects to the throttle-body was worn out, and moisture was getting onto the throttle plate. Somehow, I have no idea of why, this caused the surging idle. My indie replaced the rubber thingy, and viola! it was fixed. Never came back.

Probably of no help, but ya never know...

suginami · #3 01-06-2003, 10:39 PM

My money is on either your throttle actuator or a vacuum leak at the intake manifold. It has to be one or the other.

My problem was the same as yours and replaced the mass air sensor, then the throttle actuator, and then gave up and took it to the dealer. They diagnosed a vacuum leak at the intake manifold gasket which solved the problem.

Another user on this site had the exact same problem. He replaced his wiring harness, then the mass air sensor. Same symptoms. He read my post about my problem and asked if I kept the old actuator.

I sold it to him for $300, and it fixed his problem.

suginami · #4 01-06-2003, 10:41 PM

Another thing. My (former) mechanic did the same thing you did.

He pulled all sorts of vacum hoses off and on and nothing changed, so he determined that there wasn't a vacum leak because nothing changed.

But, there was a vacum leak all along at the intake manifold seal. Which is why nothing happened when he pulled the vacum lines off.

G-Benz · #5 01-06-2003, 10:45 PM

Severe performance problems three years ago sent me to the dealership. The tech speculated that the throttle actuator was the source of my woes before pinpointing the wiring harness as the culprit. He tried a new actuator first with no change in performance (whew!), then swapped back to the old one.

Hope it's still good...

Was going to root around the intake tonight, but wife and daughter have retired for the night (master bedroom above garage), so I will wait till tomorrow.

Keep the ideas coming...

suginami · #6 01-06-2003, 10:49 PM

Throttle actuators are a part that wear out over time.

Stevebfl said that the potentiometers wear out.

euro246 said that the harnesses on the actuators go out, too.

Who knows?

The dealer or a good independent should be able to test the part.

I wouldn't experiment on your own, though, with a new actuator. If you install it and it doesn't fix your problem, you can't return it because it has been installed. If the dealer or an independent installs it and it doesn't work, they'll just keep the part as inventory and use it for the next time.

jsmith · #7 01-07-2003, 08:45 AM

suginami,

do you have any idea how they identified that manifold leak? i imagine that can't be too common on the m104's. i don't have the surging yet but have had some signs of the throttle actuator going - specifically my cruise control which has a mind of its own(last time i checked it was working). i've also had the cold start hiccup a couple of times and attributed it to "bad gas". this winter i hold the starter until i'm sure it's caught. i've seen how the 93-94 m104's have very similar problems at the same mileage...

suginami · #8 01-07-2003, 12:01 PM

I've been told that you spray water at the intake manifold gasket to find a leak. I suppose you can see the water bubble at the point of the leakage, or perhaps the engine will run poorly for a moment as the water is ingested into the intake manifold.

I get the feeling that it's not too common.

In your situation, I'd suggest it's your throttle actuator. On M104 engines like ours, the cruise control function is integrated into the throttle actuator, and a failing / intermittent / mal-operating cruise control is the first sign that the actuator is on its way out.

Yeah, it sure is amazing how characteristic problems arise at similar mileage on these engines...

G-Benz · #9 01-07-2003, 12:14 PM

The W124 is the around-town commuter driver, so I probably used the cruise feature ONCE since I've owned it. Might take it out on the highway and see if any problems develop with the cruise control.

Couldn't find the part on FastLane...how much is that thing? I know it's expensive though...

jsmith · #10 01-07-2003, 12:26 PM

yup it's expensive. i knew about that spray around the manifold trick - with soapy water. and the other old trick was to plug the leak with soap! mine isn't surging (yet?) though. it's the cruise control and the occassional hiccup starting on cold mornings that's got me wondering. i suppose it's a matter of time...

suginami · #11 01-07-2003, 12:32 PM

The actuator is almost $1,100 from Fastlane, and about $1,500 from the dealer.

GregS · #12 01-07-2003, 01:07 PM

First off, I'm a diesel owner, so I can't say I have specific experience with the w124 gas model, but I DO have experience with this problem in a past car (a Saab 900). Here are my suggestions:

-The first thing to do is get some carb cleaner and an old toothbrush and clean out the throttle body.

-Then, if you car has what is called an air-idle-control-valve, which it probably does, take that off the car and clean it out with carb cleaner. Once clean, hit it with a little WD-40 (DO NOT USE SILICONE LUBRICANT). When its apart, inspect it for obvious signs of wear or malfunction.

-Next, if there is any kind of exposed spring which puts tension on the throttle plate, hit that with wd-40 while you excercise it back and forth.

-replace your sparkplugs

-replace ALL vacuum lines. fuel injected cars with air mass meters are very sensative to leaks, so just because you "pulled" the vacuum lines to check for a reaction doesn't mean there isn't a problem there. In fact, there mere fact that you COULD pull the line off tells mere there is a bad seal. A good rubber line that is making a tight, leak-free seal would have to but CUT off.

-try plugging the vacuum line that runs to the brake booster. You could possibly have a leak there. Although this potential problem is unlikely, the hose that runs to it could be leaking. On my Saab, not only did I replace all the small vacuum lines with silicone (which seals much better), but I used RTV sealant on all other hoses connections associated with the intake system (the one running to the booster, the one for the PCV system, etc.)

-ultimately, I think if you car has an air idle control valve, I would bet that is your problem. But all these other suggestions are relatively quick and inexpensive, so try them first.

Good luck,

Greg

suginami · #13 01-07-2003, 01:16 PM

He already replaced the "air idle control valve" which is called the mass air sensor. Good place to start because it is the cheapest item.

aldedmon · #14 01-07-2003, 03:02 PM

If there is a vacuum leak, the car will surge/die when it is hit