Benz Forum banner

1 - 9 of 9 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter #1
Hi everyone.

I have 1993 300E 2.8 with 160k miles on it. nearly year ago I started getting "hunting" in the idle.... started off very small, then before I decided to buy engine wiring harness and replace leaking head gasket, the idle oscillations were bigger.
Reading this forum I've discovered about harness and head gasket leak, so I bought harness for $750, gasket kit for $80 and replaced both.
While replacing I've found following:

The aluminum tume from EGR into Exhaust Manifold was plugged with sut. I had to get new tube because it was not possible to clean (break the sut) the old one. It was a consequence of the oil leaking into the cylinder number one (that specific location where it leaked) and then finding it's way into exhaust manifold.

Hoping that this was the problem all along to mu IDLE OSCILATION I was pretty confident that by the time we assemble this crap would be gone.

BUT IT DID NOT.... it still persists.

I start the car and it runs great once I dial the RPM to about 900 - 1000 ... but that will cause the "KICK" once you put it in "D" .... as soon as you dial that RPM down to 600 - 800 range --- the car will start going up and down in idle... sometimes it comes just to the point of suffocation, but then it strongly recovers like it's taking a big breath of air and keeps oscilating....

The next thing I'm suspicious of is the EGR valve itself and vacuum change-over valve ... maybe even idle control valve, but I have no idea where it is (ICV) ... because I have the CD manual for the car and it is pretty gloomy in the area of emissions if not even insuficient...

Please can enyone share if they had similar experience or if anyone can let me in on the papaer manual for this car (where available and how to get it) so I can diagnose certain components ... I'd be more than gratefull.

Thank you
 

·
Registered
Joined
·
5 Posts
Discussion Starter #3
OXy Sensor

Maui thanks for the reply, and I'm sorry for not mentioning this earlier:

OXY Sensor is the first thing I've replaced and oscilations were still present. Remember I'm talking about 600 - 1000 approx swing in the RPM ... oxygen sensor also only regulates "on-load" as far as I know... not on the IDLE.
 

·
Registered
Joined
·
8 Posts
the head leaking head gasket scares me. this aswell as your other issues, are tall tail signs of engine that overheated. this will cause endless nightmares thereafter. i would get hooked checked on a diognostic at a reputable benz mechanic before droping any more money in this car. get an estemate and then get another. see if this is worth the cost to repair.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #5
HEAD GASKET

Bruno, due to a known recall on this gasket and location of the leak (just above the chain tensioner) I've replaced it ... not because it was overheating. It started leaking oil on both sides of the gasket: in the cylinder # 1 and outside down the engine block. So the car runs now no problem ... it is just the RPM oscilation that is the ISSUE.

I'm thinking EGR valve and vacuum up-stream components but I wanna hear from someone who had a similar problem.

Thanks for your reply though ... it adds up to the experience bro... have a good one.
 

·
Registered
Joined
·
12 Posts
I had the same problem, poor idle but it was also running very rich, spewing black smoke on acceleration. I replaced the Air Mass Sensor, wiring harness O2 Sensor, checked the fuel injecters, and even swopped the Slide Actuator with a good one from a friends car. none of this solved the problem. I took it to the dealer and they of course double checked everything, then found the ECM to be at fault it was sending false codes, and shutting down cylinders . The car is now more responsive runs better then ever.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #7
1993 300E 2.8 idle "hunting"

Thanks ShoreBenz for your input. How much did the dealer charged you to replace the ECM? have they fixed it or replaced it? Is it fixable?

Please share more about your car symptoms and the ECM replacement and the dealer. Thank you.
 

·
Registered
Joined
·
12 Posts
The onset was sudden; revving wildly at idle, foul smelling smoke, poor acceleration would smooth out at cruising speed. I did not drive it much in this conditon. A new Engine Control Module (ECM) was installed. I've herd of them being rebuilt, and you could save money getting a used one, although, I hear this problem is becoming more popular as these ECMs get older. A used unit may need to be remapped using a Star computer in the hands of a dealer mechanic, or another MB specialist. Best bet? Find one from a 300 2.8L equipped just like yours, if so, it may not need to be remapped. Contemporary Motor Cars installed the new ECM, and new O2 sensor for $1876.50 :cry: I talked them down from $2635.00. They, like most dealers are expensive, but unlike most, they do good work.
 
1 - 9 of 9 Posts
Top