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

 

Air flow meter?
o2 sensor
has a CEL been triped or is there any stored codes?
not familar with the E's as im a C boy

 

Check your throttle switch's. I assume that your car has KE Jetronic (CISE), and it has a Microswitch on the throttle linkage, nown as a decel switch and another idle contact switch on the throttle plate. The one on the throttle plate has three wires, with one wire being the idle contact, one for full load and one as the common.

If you can get hold of a good quality multimeter, you can measure the on/off ratio also known as Lambda at the round diagnostic plug. This readout can also be used for diagnostics, because if it displays a constant ratio, that can be used on the fault code table. Let me know if you have one of these multimeters, or a Lambda guage.

 

dondas do you know any easy or cheap way to clear my fault code stored it is for the airbag, and was stored after once i took my dash out and turned the key on to listen to radio [sm=badidea.gif] and now when i turn my car on the srs light stays on for like a minute b4 it goes off and it is annoying.
I just dont want to take it to the dealer and pay big $$$ to clear one code
1994 c280
cheers for any help

-sorry for stealing topic-

 

Hi C280,

Unfortunately for you, I have a diagnostic computer which I use to clear SRS fault codes. I have never needed to try to find out another way to clear them, and I have never heard of another way.

However, it may still be possible. I have just read a diagnosis manual on the SRS sytem, and it uses a pulse output to display codes ,which is picked up by the diagnosis computer. On the earlier versions, we used a pulse counter which reset codes by either earthing or connecting to positive the diagnosis output wire in the diagnosis socket. Don't try this yet. I will try to find out more for you.

 

Thankyou dondas

 

I have checked this out for you C280, and it would only be possible if your car was built before 30th of June 1993. It was up until then that they used the impulse counter system for diagnosis.

I put a fault into a 95 E Class which uses the same sort of system as the 94 C280, and must concede defeat. I tried all sorts of things, but had to resort to the diagnosis computer to clear it.

Sorry, but I think you may need to visit a dealer. Visit your dealer, and explain what you did, then see if you can get a cash job with no invoice. Should be very straight forward for them. You might spring it for a bargain.

 

yep.
Thank you for trying!!! very much appreciated man
-i should be able to butter up one of the local merc workshop guys for that, as i have a relatively rare car c280 manual pritty modded and he also had a manual merc and was young like me and gave me heaps of help and talked crap for like an hour with him so hopefully beers :-).
Once again thanks

 

I had a similar problem on my BMW...

If youve already ruled out your o2 sensor and other items dondas suggested... it turned out to be the engine temp sensor on my little bimmer. It also had the computer running the air/fuel mix rich and killing my cat... nox levels were failing, once we changed that part,(which cost like $6 from the dealer) the idle smoothed out, the nox came down and fuel economy improved.

I hope you get 'er done!

best wishes
WQ

 

Dondas

I had exactly the same problem on a '98 E320.
replace the Mass Air Flow Sensor... Get an OEM MAF and you will be good to go. (((don't get aftermarket, they cause the same problem out of the box.))) I learned that the harde$t way po$$ible.... time AND money.

Good luck and happy motoring.