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.

__________________
2007 C 230 Sport.

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...

__________________
John Shellenberg
1998 C230 "Black Betty" 240K

http://img31.exs.cx/img31/4050/tophat6.gif

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

__________________
former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL

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....

Have any ideas??

__________________
former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL

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

__________________
2000 C230 Kompressor "Frosty"

2007 PT Cruiser
2001 VW TDI Beetle
1999 Landrover Discovery II
1971 Corvette

Gone: 97 Cabrio, 83 240D, 93 VW Eurovan, 95 Volvo 850, 93 Chevy Astro Van, 77 VW Bus, 99 VW Jetta, 74 VW Bus

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.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

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