C 230 Rpm Idle Fluctuation
 

WELL after throtle body clean its still there.

AT IDLE RPM'S GO DOWN THEN BACK UP WHILE IN DRIVE AT STOP LIGHT AND IDLING, NOT EVERY TIME. OTHER THEN THAT NO PROBLEM WITH ACCELERATION AND CEL NOT ON. AFTER ENGINE IS REALLY WARM IT WON'T DO THIS. INDY MECHANIC SAID DIDN'T DO IT TO HIM SO DOES NOT WANT TO JUST START REPLACING PARTS.

WHAT WOULD CAUSE RPMS TO FLUCUTATE AT IDLE?

SPARK PLUGS CHANGED 6 MONTHS AGO AND NOTICED IT AFTER ONE MONTH. CAN THAT DO IT.

1998 C 230.

HELP, TIRED OF PAYING THESE GUYS THAT HAVE NO IDEA, OR NO EXPERIENCE.

Did you install the correct sparkplugs?

Air pump self test. Normal. Didn't we have this conversation already? Turn your caps lock off, it's annoying.

If the car experiences a 1-2 second dip in the idle, with a "shudder," then runs fine the rest of the time and no CEL, then what you're experiencing is the air pump self test. I've owned my C230 since new, for 240,000km now, and it has done it since new, and always will as long as the air pump is working properly.

You can keep throwing time, money and effort at solving this problem, but I doubt you will ever be satisfied. The car has a normal system operation that causes a slight idle drop. Get used to it.

Don't clean the Air Mass Meter. You're asking for trouble. They were not meant to be serviced, and even if it was failing, at best you bought a little time. The failure of the AMM causes a fuel trim adapation problem and is easy to diagnose. First, 95% of the time it will throw a CEL then you'll have a terrible hesitation at 4500rpm and above. Driveability will be effected.

Now that you screwed with the AMM, I'll bet that sometime in the not-too-distant future it will go out on you. If you get code P0170/P0171, then have the adaptations read and I'll bet they be maxed at 1.32 and you'll need a new AMM. BUT, the symptoms are different than what you're describing.

See my post above.

YES

I cleaned T.B. and not M.A.S.

COULD incorrect plugs or not tight enough cause this same symptoms?


Sorry for capital letters, just tired of mechanics who are supposed to know about abnormal and normal variants.
:mad:

I AM asking because for 100,000 miles this vehicle has not done this self pump air test SO not a normal variant and very noticeable! Only real change are spark plugs.

COULD IT BE PLUGS, NOT RIGHT SIZE,OR TIGHT, LOOSE?

What plugs did you install?

I Didn't Do It, Mechanic Stated He Went
To Dealer For Oem Plugs.

Can Plugs Cause These Symptoms?

Try this:
Turn the key to " ON ". ( DO NOT START the engine ).
Push the gaspedal ( slowly ) all the way to the floor.
Hold it there for 10 seconds.
Release the gaspedal.
Leave the key " ON " for 2 minutes.
Start the car & see what happens with your idle.

What Am I Looking For?

BEFORE I do steps i have to know what i am/am not looking for and to

diagnose what exactly?:o

Read sticky post #1 at top of page.

On my 99 the procedure in your thread, post #9, will reset the trans adapation values.

Man, this thread is all over the place! Spark plugs, Air Injection, Transmission adaptation, etc. The answer probably isn't too hard to find, as long as you look in the right place. I realize not everyone has SDS at their disposal, but here's what I'd do if I was working on the car.

It sounds as though the throttle actuator could be the problem. The first thing I'd do would be to make sure the fuel trim values are within specification. This is a reliable, fast way to eliminate the possibility of a lean/rich condition causing the problem. If that checks out good, I'd activate the throttle actuator using SDS. It's a simple test, done with the engine at operating temperature/idle speed. The throttle is slowly closed, lowering the idle in small steps. Then I'd see if I was able to open the throttle up again. Sometimes the actuator simply isn't strong enough to overcome the throttle return spring. I see lots of this on higher mileage M111's. The result is a fluctuating idle because the actuator doesn't react quickly enough to stabilize it.

I am not sure I am clear on the EXACT symptom. Is it:

A) Fluctuating idle

B) Idle drops ONCE for 1 second or less and that is it, until the next time you drive the car from a cold start.

A or B?

When car is started it does not do it, never does.

I can drive 20 miles at 60-80 m.p.h. without problem after that, then when at first long stop light, R.P.M. CAN go down slightly then back up to normal. NEXT light it may do it again and thats it for rest of drive.

IT will do it 2 miles from my house at stop light or stop sign, so not necessary for completely cold car, but after stop and go for a while it may do it again.

NEVER a loss of power at high speeds, no cel.

I CLEANED t.b. THEN CEL CAME ON AND OFF AGAIN without those jerks forward 2nd or 1st manual gear thereafter gone.

Fluctuating idle, goes down not up, for a second and not necessarily from a complete cold start, it can do it 1 or 2 and thats it until car driven hard stop and go then only on occasion when it is really hot. car will not die.

VACUUM HOSES CHECKED.

I AM CONSIDERING NEW PLUGS, THAT THE REASON FOR QUESTION IF THAT COULD DO IT SINCE THAT WAS ONLY CHANGE. plugs done 6 months ago.

THAT was my point on above post.

WHAT COULD IT BE?

Mechanic mentioned cleaning throttle body from get go but still there.

SENSORS? O2? THROTTLE POSITION SENSOR?


I DON'T KNOW SDS IS?

I THOUGHT IT MIGHT HAVE BEEN EASIER TO FIND, BUT I GUESS ITS ONE OF THOSE THINGS THAT YOU GOT TO SEE IT, BUT TECH HAD IT FOR 10 MINUTE DRIVE AND HE DIDN'T NOTICE IT. I got car back drove 30 miles at 70 then at first stop light, RPM down fron 800 to 400 , then back up!!!

Do exactly as he says!!!!
SDS = Star Diagnostic System, any M-B dealer has this.
Quit guessing and do as you're told. :rolleyes:

So The Throttle Position Sensor Is Probably Not The Problem?


If Actuator Is Prob Then New One?

Do not throw parts at it. You'll be broke and sorry. Get the car onto an SDS and have the adaptations read and see if there are any codes present. If the adaptations are out of whack, then you'll be onto the track for a good diagnosis. If the fuel trim is fine and there are no misfire codes present, then button it up and drive it until something does show up.

You need either a dealer or a good MB indie that has SDS. Forget ANY OTHER mechanic/shop, they will be of no help to regarding your MB.

As for just going ahead and replacing the throttle actuator without proper diagnosis, it's nothing but your money, but wait until you see the price of the part...

Part 650 Dollars At Local Foreign Parts Store.

[QUOTE=LORE BENZ;1705709]When car is started it does not do it, never does.

I can drive 20 miles at 60-80 m.p.h. without problem after that, then when at first long stop light, R.P.M. CAN go down slightly then back up to normal. NEXT light it may do it again and thats it for rest of drive.

IT will do it 2 miles from my house at stop light or stop sign, so not necessary for completely cold car, but after stop and go for a while it may do it again.


You have the same, exact symptom I've had for 3 years and about 100k miles. It was never resolved under Starmark warranty. I've learned to just live with it. I've had a new AMM for other reasons, no change. It's clearly the air pump. If I'm at a light, beside a car with my window down, I can hear it do a blip-whistle that corresponds with the RPM drop. After I've driven the car for at least 20(ish) minutes, it stops doing it. It is a rythmic deal. About every 5 secs, perfectly timed.

I've tried putting it in neutral at lights and it's a lot less noticeable. The RPMs dont go up as much, I guess because the motor is not fighting the torque converter to maintain RPM.

Again, this symptom has eluded SDS, 3 sets of copper OEM plugs, multiple air and fuel filters, replaced trans electronics, pretty much any and all maintenence plus some Starmark repairs over 3 years and 100k miles. Take that FWIW

thanks WILL,

It didn't do it today at all, thats how it goes. After 20 STOP SIGNS AND 15 LIGHTS!

The only thing i will ever do at dealer is have them diagnose on machine.

Mine will do it 1 to 2 times and only at long stop light or sign.

LIKE I SAID INDIE MECHANIC, and I drove with him in car, did not stop long enough and wont do it.

YOU obviously know what is going on with yours, why isn't there a fix??

SOME tell me THROTTLE ACTUATOR.

Before changing that part one better be sure due to high price....

MB Doc
 

Have any ideas??

Lore, it seems to me that Will already told you, that it's a "normal" self test to have an idle surge during long idles. Spark plugs won't do it, because it would do it all the time, or at random times. The fact that Will's car does it at exact intervals means it's some sort of computer self check. Your car has a very complex computer, that tries to get past emmissions, while making lots of power, and maintains drivability around town.

Several people have said the only way to find out is to hook it up to the right computer (SDS) and see if it has a problem. If the computer says it's fine, live with it. Without the computer, buying parts because someone told you is a waste of money.

Please, please turn your caps lock off, it's really anoying to try to read your posts.

Chuck

Mine is random and does not need loong intervals to idle.

Had not done this for over 100,000 miles and noticed it now.

Complex and expensive parts yes, throw money at it, H*** NO!

Will did not mention THROTTLE actuator.

If mine was cyclical like ac surge, I can understand. But it isn't.

Therefore asking opinions and got a few.

A SURGE IS UP, MINE IDLES R.P.M. DOWN THEN BACK UP!

TODAY it didn't do it once after over 60 long stops, this can happen the next day 2-3 times though.

This is why I asked question of what could it be for people who really know how these machines work, no novice please???

YOU got PROFESSIONAL advice a LONG TIME ago partner.

See post #13.

Many of us don't get that in our posts, you did. Use it to your benefit.

GOT EXACTLY same advice at other post, I know both of these guys are not
newbees!!

I think you have what I have. Here are my exact symptoms:

Once (or maybe twice) a day, at a stop, after fully warmed up, the rpm stumbles for about 1/2 sec. That is it. No other symptoms. It is a curiosity.

Is that exactly as what yours does?

[QUOTE=N41EF;1707142]Lore, it seems to me that Will already told you, that it's a "normal" self test to have an idle surge during long idles.

I never said it wass normal. Doing it for excessive lengths of time would tell me that something is wrong with the pump or emissions system, but in 100k miles there have never been any diagnostic codes related to these symptoms.

I have learned to LIVE with it, but it's not normal

I think both Lore and I have the same issue Mike - mine will do it for 2 minutes, the quick "blip 'n dip," multiple times, ryhthmically. It's not a 1 or 2-time deal at first startup. It's a lengthy annoyance that is definitely abnormal, but again, in the OP's defense, the "great advice" of checking the system with SDS is probably futile. Neither of my local dealers could determine a "problem" in teh past

So, now it comes down to ingenuity - and I would think a failing throttle actuator would cause the problem ALL the time, not just for the first 20 mins

Please let the poster answer my question Your Honor!

Of all the posts, I'd say this one is the best (and hey! He's a tech so he should know ;) )

Next time I'm in for service, I'll see if I can bribe my service writer with a Panera lunch card (saved me $120 last time :) ) and get some reduced-cost disgnostic time. I will point him in this direction, ILUVMILS

Lore, I'd say this is out best best - specifically, the lean/rich/fuel trim issue


Mike, sorry for hijacking! - just trying to help because I am 100% certain our problem is the same

Mine does not last for 2 minutes, more like 2 seconds at stop light, did it today only one time and that was after 20 minutes of driving at long light.

R.P.M. dips down and back up to normal once only during the whole stop of 1.5 minutes. OTHER TIMES TWICE, but not at same light or stop.

IF I TAKE LONG 2 HOUR DRIVE, NO problems at all!!!!

IF it is rich mixture, what can tech do about it?

SOME dealers are notorious for fixing that and selling throttle actuators, PARTS CHANGERS IF YOU EVER HEARD TERM. Thats why I am leaning to someone who has machine or dealer to ONLY DIAGNOSE if anything wrong.



THAT IS MY CONCERN!


WILL, THROTLE BODY IS NOT CHEAP, so better be sure that is cause of problem before changing it and RPM DIP is still there after that!!!!

So I think from what you say that you have the same as I have which is not as bad as what will_w202 has. If I understand correctly this is simply a curiosity and does not effect driveability or performance in any way. Is that correct?

If so what is the big deal?

I think to put this to bed, you could do an EXPERIMENT:

Unplug the air pump motor (I assume it has a connector). Then I believe your symptom will disappear. Also your CEL will probably go on since the pump will "fail the test". Also your emissions will be worse. Then plug in the pump and the symptom will return. Then you will know if it is the air pump or not.

yes!!!

But I don't know how to remove 'air pump motor" and wait for one day or two to see if it will do it again???

HOW DO YOU FIX RICH/THIN MIXTURE if that is problem?

Is that normal to dip like that?

Do you need to replace air pump motor??? expensive!!!

THROTLE ACTUATOR???

MY symptoms are as I stated above, very specific.

SO what parts or problems can do this ONLY??

We're going to talk this thread to death. The probable culprits have been identified. I'd do the tests prescribed in previous posts, starting with disconnecting the air pump as was just stated. I don't think you NEED the air pump, it's just a $700 part that makes the EPA happy by changing the fuel mixture during cold starts to lower emissions. If mine ever dies, you can rest assured I won't be replacing it.

Eliminating the air pump won't cause any drivability problems. You'll just have to get used to driving around with the Check Engine light on all the time. :(

THANKS FOR POST GUYS, I APPRECIATE IT!!!!


I am going to drive car as is and if decent indie shop with SDS machine pops up I will consider hook up with this rich knowledge in hand!

In the meantime if ones with similar symptoms get fix, chyme in with news of fix or no fix after car care.

IF I had to bet though I WOULD bet on throttle body!!!!

Yeah, but there's got to be a way to close the circuit or something at the connector, right? Bound to be a way to fool the light :)

It's not quite that easy. The engine management system checks the Air Injection system by monitoring O2 sensor voltage during air pump activation.

When the air pump is running, the O2 sensor voltage drops dramatically. This is how proper air pump function is verified by engine management.

SO WOULD YOU recommend removing TUBE TO AIR PUMP AND SEE IF IT DOES IT OR WILL THAT CAUSE OTHER PROBLEMS?

Sorry for the confusion. Will 202 and I were discussing a different issue.

What I meant to say before is unplug the electrical connector to the air pump motor, as an experiment. If it ever stops raining here and is light outside at the same time (unlikely) I will pop the hood and try to locate where the connector is for you. This SHOULD be an easy test to do, provided the connector is accessable.