Increasing idle - PeachParts Mercedes-Benz Forum

ssanmor · #1 05-05-2004, 10:44 AM

My "new" 190E 2.3 1992 belonged to my brother-in-law, who assures me that that car was once adjusted so the idle was at 1000 rpm, and ran noticeable better, at the expense of a higher fuel consumption. But it had to be readjusted again so it could pass the emissions test.
The only thing that I can imagine the garage touched is the fuel mixture adjustment, but I can't figure out how can it be set to run richer, as I have tested that the lambda control is working properly (around 40% +/-5% duty cycle at both idle and 2500 rpm) and so it adjusts the mixture itself.
Perhaps they set it way too high so the ECU doesn't have margin to compensate for so a rich mixture?

He told me that the car ran about 1 year that way, and that there wasn't any noticeable damage after it was re-lowered. This was about 4 years ago and now the car runs good and passes the emissions tests perfectly.

What are the potential dangers of setting the mixture too high? I can only think in the cat, but 1 year is time enough to have blown it, but it seems it hasn't.

What do you think, does it worth the pain re-setting it that way again? (leaving the emissions apart ;-)

Best regards

henryk1 · #2 05-05-2004, 12:18 PM

An excess rich mixture is not good.......the worst scenario would be excess gas washing the piston walls. Over time this will shorten the life of the piston rings.

The best (and only) proper way of setting the mixture screw is with the use of a CO/HC gas analyzer. This is done with the O2 sensor disconnected.......to get the proper baseline setting.

If yours is a KE-Jetronic CIS system, then the idle is adjusted using the air-bypass screw........a large knurled screw with an Allen head on it. It is found on the throttle body.

Duke2.6 · #3 05-05-2004, 04:49 PM

In closed loop operation the mixture is maintained at stoichimetric except at WOT. The idle speed is controlled by the ECU and is not adjustable, other than the basic adjustment to keep the idle control valve duty cycle in the proper range.

The basic mixture adjustment is okay if the car starts and runs well when cold and the duty cycle is in the correct range, which appears to be the case with your car.

It's not broken. Don't fix it!

Duke

ssanmor · #4 05-06-2004, 05:45 AM

Well, the idle is quite low, about 700 rpm.
The question about enrichment was only to know what was done to the car, and to gain performance, but want to be sure at what cost.
Henryk, about the idle adjustment, I believed that it was a screw in the left of the, just under the airbox, but it is only present in early models. No screw in my car, unless you are talking about other screw. Can you confirm this, please?

Another thing: I have noticed that my idle is a bit more rough and low after having changed my air filter and distributor rotor. Is this normal until it wears a little bit? (I haven't changed the distributor cap as it seemed ok)

Thanks.

ctaylor738 · #5 05-06-2004, 08:10 AM

No, those items do not have to be broken in. You might check and see if you knocked a vacuum line loose while you were replacing them.

sbourg · #6 05-06-2004, 08:46 AM

Quote:

Originally posted by ssanmor
Well, the idle is quite low, about 700 rpm.

Another thing: I have noticed that my idle is a bit more rough and low after having changed my air filter and distributor rotor. Is this normal until it wears a little bit? (I haven't changed the distributor cap as it seemed ok)

Thanks.

700 is correct. The rough idle should be addressed without attempting to change idle speed, which is set by the ECU monitoring engine speed. Look at night for signs of arc-over causing misfire. A new rotor might make it worse if the problem is tracks in the distributor cap, or between wires. Overly wide spark plug gap or using platinum or other incorrect plugs is a likely cause.

Steve

ssanmor · #7 05-06-2004, 09:47 AM

I am using 4-electrode bosch plugs, and they seem to work ok. I haven't changed them now, so the difference can be in the rotor, I will try with the old one to see if there is any difference.
BTW: Do you have a smooth idle? What sparks do you use?

Thanks!

sjsfiji · #8 05-25-2004, 01:45 AM

Hi,

I've read a lot of posts regarding why MB approved plugs should be used. I think it's because the resistance is built into the wire and jacket (1 K-ohm), and non-approved plugs may have resistance built into the plugs which adds to this (not recommended)... just FYI...

I use Bosch h9dc w/ 1 yr old cap and rotor (smooooth)... Also, never pull on the wire but only on the jacket with long-nose or specialty pliers or damage to the wire/jacket connection results...

good luck,