M103 91 300SE idle air valve
 

Is the idle air valve in a 91 300SE controlled by pulsing a 12V signal or by modulating the current?

What should I expect to happen if I pull the electrical connector with the engine running? RPM should go up, right?

Thanks,
Sixto
95 S420
91 300SE
87 300SDL
83 300SD

I think it's the same as the 300TE -- current modulated, idle should rise to 1200 or so with it unplugged.

Unless it's stuck, anyway.

Peter

It looks like a rotary valve of some sort. Does it spin all the way around or does it twist back and forth?

Thanks,
Sixto
95 S420
91 300SE
87 300SDL
83 300SD

The one on the M103 is a canister with a two-nipple fitting on the end. The actual valve is a "flap" that moves in a rotary fashion to cover the hole on one nipple. It's held open by a spring, I think, and closed by current.

they get gummed up from fuel residue and stick closed on deceleration, then fail to open fast enough as the engine slow down, causing stalls. The other failure mode is usually to quit altogether and the idle speed goes way up.

Peter

Neither symptom fits my situation. Butter smooth above 1200 rpm, idle is stable but shakey at 600-700 rpm with economy gauge reading half way in D with AC on.

The flapper thing inside the idle air valve moves freely and I don't think I can get it cleaner than it is.

Hoses look good. I've sprayed all around with carb cleaner and haven't found any leaks.

Argh!

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Hmmm. Now why does this sound familiar?

Check ALL the vac lines, especially the one for the computer on the fender. If at all iffy, replace. How hard are the hoses on the idle control valve, and does the modulator hold vac? What about the climate control?

Check the mixture too -- the TE was doing exactly this before I fixed all the leaks. Shifts better, sounds better, etc.

You should also consider the possibility that the cat is plugged or the O2 sensor is shot, both will cause idle running problems. The cat will cause sluggish performance and poor milage as well. The O2 sensor will cause overlean running.

And it is possible that the valves guides are worn enough to cause idle problems. I'm not too worried about mine, they are only 40,000 miles old, but if you have lots of milage on there with no head work, they can be a problem.

Peter

I removed and capped the AT, ACC and EZL ports - no difference. Hoses are flexible and no visible cracks. The car was tuned to pass CA smog at an indy < 4,000 miles ago - I'm sure he would have said that it needs an O2 sensor. It could but it doesn't run any worse now than then. I was too cheap to have him run a proper diagnosis :rolleyes: Less than 500 miles since new valve seals were installed. I haven't checked EHA current and duty cycle yet.

Thanks,
Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Old tired injectors will also cause different fuel flow to each cylinder, with the result that some run rich and some run very lean to get the correct mixture at idle, so it runs rough. Smooths out as speed increases and the amoutn of fuel running through the injectors incraseas. New injectors are in the works for the TE, once I get a few bucks ahead somehow.

Peter

I've thrown enough parts at this thing that anything more isn't worth it. Injectors, holders and seals are new within the last 4000 miles.

I installed a new O2 sensor just now... no difference. I don't know if there's a break-in period. I've never heard of it.

The EHA sees about 7.5ma at idle. Dips to 2.5ma with revs. I just figured out where the X11/4 port is so I'll check duty cycle next.

Oh, I pulled the idle air valve connector while the engine was idling. Idle dropped to 500 rpm, maybe a shade lower. Wouldn't hold idle with AC on. I reconnected the idle air valve but no improvement unless I shut off the engine, cleared the check engine light and restarted. Then it was fine... or back to its previous self.

Thanks,
Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Mr. Sixto. Why not check the potentiometer?
 

Sixto, try to check the Air Mass Flow Potentiometer. The voltage

between pin 2 a ground has to match .7 volts +/- .25V it means

700 Mili volts +/- 250 Milivolts.

Read the Sbourg, DaveCT, Chris Martens Threadid on 05-25-2003 till 06-27-2003.


Good Luck

As Mario stated, the problem might be the airflow sensor pot. It is located on the front side of the airflow sensor body with three wires going to it. There is a wiper arm and semiconductor printed circuit board that sends the airflow plate position information to the ECU. The pot gets worn out, especially in the idle range area, and causes erratic idle, surging and stalling.

I replace the one in my '88 260e and it idles perfect now. I purchased the part from Olyparts.com for about $75 and saved the cost of a new airflow sensor.

Hope this helps,

John

Mario,

Is that voltage to be read while the connector is connected and the engine idling?

Thanks,
Sixto
95 S420
91 300SE
87 300SDL
83 300SD

READING 700 MILIVOTS AT MASS POTENTIOMETER
 

tHANKS SIXTO.

Leave a small slove when coneccting the POT socket for

contacting the Red cable of your DMM to the POT. PIN 2. The

black has to go to batteri nagative pole.


Please read my Threadid on 10-19-2003. "THANKS TO SBOURUG, CHRIS MARTEEN, DAVE CT, MODERATORS AND ALL SHOW FORUMS PEOPLE.."



mARIO fARIAS
laprefar@cantv.net