85 MB 500sel Air Flow Meter Tower Replaced

[Chamariver]

My car would not start after new Air Flow Meter Tower replaced. Well I made adjustments about 1/8 turns clock-wise until the car finally started, then turned screw in tower CW until engine started to run rough, then back until it started running rough in the CCW direction, then found a happy medium in between. Engine now starts and runs ok, revs smooth with good response.

The engine idle ran a little rough until the Idle Control Valve came on, and this was only after the engine was warmed up a little. (have a little bulb connected to the two wires so I could see when it came on) When it did come on the engine idled much smoother, and dropped from 1100rpms to about 750. Does someone know why the Idle Control Valve would take so long to come on?

I notice one other thing that does not seem right. The fuel "Economy" gauge's needle, at idle, is not near the far left (black area) but instead is a little into the beginning of the red bar, just pass center. Anybody have a idea what is causing this, and how to fix it?

[Chamariver]

Update: I still have the issue with the "Economy" neddle being in the red when at idle, but here is where I'm at now.

I cleaned the idle air control valve with carb cleaner, even though it was working fine before the cleaning. When power is put to it, it functions as required. I did some adjusting of the allen screw in the air mixture tower and have got it to where it does not idle up and down anymore.

But now, when I turn on the key to start the engine, it starts with no problem, idles at around 750rpms, revs smoothly, no missing, but the idle begins to climb to about 1200rpms as the engine gets warmer, in about 4-5 minutes. It then holds at 1200rpms and does not come back down to normal idle of 750rpms. I had connected a small bulb to the two wires connected to the idle air control valve and noted that no power was going to it, except one time and that time the valve was activated and the engine dropped to normal idle speed of 750rpms.

I have several Idle Control Units, which I have switched out, and same with the Fuel Relay. All are working ok, but the power going to the Idle Air Control Valve is most of the time not getting to the valve. Whenever the valve does get the power the idle is as normal.

[pmckechnie]

Look around the center if the firewall and you will see a Idle Speed Controller that is aprox 4 in wide, 1 1/4 in thick, and 4 1/4 in tall. The plug is on the bottom of this controller. Remove the 10 mm nut on the drivers side, Pull the controller away from the firewall on the drivers side then slide it toward the drivers side. Pull it up so you can see the plug. Start the car. As you hold the controller in one hand, move the cable around with your other hand and see if the idle changes. If it does, you have a connection problem in the plug, bad solder joint in the controller, or something else causing a connection problem.
If the above makes the problem come and go, then spray some WD40 on the plug and the controller pins.
I had this problem 5 or 6 years ago. Cleaned the connections and the problem was gone.

Paul

[Chamariver]

I pulled the Idle Speed Controller and while car was running moved the plug around and nothing happened, nor did the little bulb come on that I have connected to the two Idle Air Valve. I then, while the car was running, took another of the spare Idle Speed Controller units I have, plugged it in and tried the same thing, and got nothing from that one. But, I then got the 3rd spare Idle Speed Controller unit and plugged it in while the car was running and the bulb came on and the engine died.

I tried the same procedure all over again and got the same results. Now, when I used the first two Idle Speed Controller units the car will start (easily), without having to put my foot on the pedal, and idles at 1200rpms.

But when I try to start the car with the 3rd Idle Speed Controller unit (the one that bulb comes on, but kills the car when idling) it will not start without pressing the pedal down a little, and will die if I take my foot off the gas. I have to hold the pedal down to keep it around 800-1000rpms to keep it running. It's like the Idle Air Valve is choking/cutting off the air which makes the engine die.