Being a Mercedes Benz enthusiast for more than 30 years I cant belive I didnt know about this site!
Great people and tons of info.for making MB ownership a pleasure.
This is my first post so I would like to say hello to all fellow forum members and the same time ask for your help on my 93 300E 2.8.
Couple of month ago eng(in normal operating temp)started a serious idle flactuation(between 700 to 1200RPM)it does this only when trany is in park or neutural,here is the list of the items have been replaced:
ECT sensor
Idle/cruise actuator($900)
wirring harness ($600)
OVP relay
O2 sensor
Induction system is tripple checked for false air,no lock so far.
Any thoughts in this matter will be highly appreciated.

Best regards Rasoul.

Yikes!

You've sure covered all the usual suspects.

Checked the ignition system? Plug wires, ignition components?

Mass Airflow Sensor? Does it read a code on pre OBD-II cars? I don't know. Our Mazda did the EXACT same thing, and it was the MAS. Before you get shocked by the MB MAS price, I'll tell you that a new Maxda one for our 1988 626 was $1300. The dealer GAVE us a used one for nothing...

Vacuum leaks?

I'm at a loss. With new harness, OVP, and O2 sensors, this is a bit of a stumper...

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John Shellenberg
1998 C230 "Black Betty" 240K

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

Howdy, John
Appreciate your reply.
FYI In process of Idle/cruise actuator replacment I renewed intake man. gasckets.Being a pre 1996 car it is not OBDII capable but I could retrive some codes of the ECU which indicated ECT and intake air temp sensors mulfunction,well the ECT and IAT sensors and wirring harness are new,still gives me the same codes.
It is hard for me to imagine IGN sys is causing this since as soon as you shift to R or D Idle stablizes immidiately,also it idles good when the eng is cold(for 3 to 4 min).

Makes sense, but I'd check just to make sure. After all, everything else has been done!

Fuel pump relay? Wrong symptoms...

I thinks it's funny that you'd still get those codes after replacing the parts...hhhmmmm.

I'd still have a go at the intake system again. As I said, our 626 had the EXACT same symptoms, and the MAS was the problem. It didn't show a code, but the tech had a hunch. There MUST be something in idle control somewhere that's causing this. Fuel management? Air managment?

This is an HFM equipped car, not CIS.

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John Shellenberg
1998 C230 "Black Betty" 240K

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

The mass air flow sensor is the most common reason for idle fluctuation on the 104 engine.

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Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS

Hmmm...I have the same idle fluctuation problem...but mine acts up in D or R (especially R)...more prevalent in warm weather than cold.

Swapped out the air flow unit with a new one, and the problem persisted, so I returned the new one.

Was I wrong for doing this?

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Hello G-benz
Wish I knew a part supplier like that,to accept return on electronic part like mass air flow sensor.LOL

Thanx Donnie'

Found a company here in Houston they'r gonna let have a air flow sensor for diog. purposes,whish it takes care of this problem.I think the end result could bring good info. for every body,so I'll keep you posted.

Best regards Rasoul

i had the same symptoms on my old buick, a 3.3L v-6. Mass air flow sensor fixed that problem. We went through 3 of them before we finally got a good one. After the second one i finally got fet up and took it somewhere, they lightly tapped on the MAS and the engine started runnign completely differant, he then closed the hood, wiped his hands, and said "thats your problem". I then told him it was brand new and it was the second one and he shook his head and said again "thats the problem". I said ok, replaced it again(luckily they had a good return policy). INstalled it there, low and behold, no more check engine light(for a week at least, thats another story) and the car idled great. sorry for rambling
Ryan

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83 300SD.......sold
96 integra SE....sold
99 a4 quattro....sold
2001 IS300.......sold
2002 330i.........current.
2004 highlander limited....current.

Good Morning gentelmen!
Special thanx to Donnie,Ryan,G-Benz and Blackmercedes.
You guys made me feel like a happy camper,couldent belive I can get in touch with so many knowledgable people within click of a keybaord.
The beauty is up and runnig like Rolex watch(may be Rolex watch should run like Mercedes),problem was in the mass air flow sensor,picked one up this morning,got the eng running till reached normal temp.,Idle started falctuating,shut it down,installed the new MAS,started up and VOILA!!
Thanx again.

Best regards Rasoul.

Glad to hear your problem is solved.

__________________
John Shellenberg
1998 C230 "Black Betty" 240K

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

i'd take the rolex anytime!! he, he!!