Strange whistle, ABS light and other woes. - PeachParts Mercedes-Benz Forum

RichardLSU · #1 10-21-2010, 10:22 AM

Car: 1985 300SD

If I'm driving down the road, with the fan/ac/heater on, once I "level out" I begin to hear a high pitched whistle noise some of my friends have mistaken for the turbo whine. If the fan is off there is no noise. The moment I let off the throttle or increase it the whistle stops momentarily, until the car "levels out" again. After recently doing an intake modification, I removed the EGR and ARV lines and plugged them up, along with making plugs for the EGR and ARVs respectively. I immediatly noticed that this whine was gone. The car ran like crap so I hooked them both back up and the whine has returned. This has been a constant mystery for me, any ideas?

Second, recently, since the weather has started to get cold, for no particular rhyme or reason my ANITLOCK light has been coming on on the dash. I'm not sure I'm feeling any real difference in braking power but it worries me. Might I have a sensor going out? When I start the car it will either come on or it won't. If it does come on it stays on until I stop the car and shut it down. When I turn it back on again it might come on, or it might not. I can't seem to figure out the variable here.

Third, my heater. This thing seems to have a mind of its own. If I turn on the car, and let it idle, it heats up real nice and toasty. But while I'm driving down the road it seems to blow only cold air. When I come to a stoplight or stop for any period of time, the car will warm back up again. I know its going to be cold here in a few months and would love to have this taken care of.

I've been having A/C problems and one of the things suggested to me by my mechanic was to replace the little flaps that cut off the outside vent. My a/c is working great now, but not as cold as I feel it should be. He said that by replacing those flaps it won't let outside air in and it will be recirculating the cold air already inside the car. Could this be the source of my heater problem too? Any input is greatly appreciated.

Thanks guys! This car of mine would not be running if it wasn't for all the great information provided to me by this forum!

cirrusman · #2 10-21-2010, 11:54 AM

About the whistle, I'd make sure the EGR and ARV are in good shape... You can use a soapy water solution to check for leaks.
Mi 300SD is an '83 so I don't know the first thing about ABS, but it does sound like a sensor...
About the heater, my car does exactly the same. I have been told that I'd have to replace the pink vacuum actuators that tend to go bad with years. These are all behind the radio panel and dashboard. Instead of messing with the flap I'd just check the actuators, vacuum system and fix and replace as needed.

4thesporty · #3 10-21-2010, 12:26 PM

I just went through the ABS thing on my car. The question is, does the light come on as soon as you start the car, or does it come on after you have driven forward for a couple of seconds?

The "flaps" you are talking about for the recirc is behind the glove box, when you push that door open that is full recirc, when it is all the way rearward, that is all fresh air. I would recommend taking out the glove box and observing how it behaves while driving. While I was looking for replacement pods for my car, I propped that door to full recirc using two wooden dowel rods.

Sorry, can't help on the egr, arv except that when I plugged them both and removed the egr I got a little more low end power. I also removed all the vacuum tubing and switchover valves for them at the same time.

4thesporty · #4 10-21-2010, 12:28 PM

Check my thread here for some numbers on testing the ABS wheel speed sensors:

ABS Wheel speed sensor

RichardLSU · #5 10-22-2010, 01:04 PM

I noticed this morning that it came on after I had put it in gear and moved forward. Right after I moved forward.

Any pictures of these pink valves?

I'll try the soapy water thing maybe this Sunday and check for leaks. I also noticed that as soon as the whistle stops it seems like the boost kicks on. Its already there, but feels more "solid" ---if you will---. Almost like a release valve closes.

4thesporty · #6 10-22-2010, 01:44 PM

Since the ABS light does not come on until after you drive forward, this means that it is more than likely one of you wheel speed sensors. You have three total, one on each front wheel and one on the rear diff. The first step is to get under the car and remove the one bolt that holds the sensor in, 10mm IIRC, pull out the sensor and clean it well with brake cleaner. It is magnetic so it will be holding alot of crud more than likely.

After the sensors are clean, spray the brake cleaner into the area where the sensor was and rotate the wheel while doing so, you will see all the caked brake dust and crud come out.

Do this with each front wheel, and clean the one off the rear diff.

If this doesn't solve your problem, you need to unplugg each sensor from it's harness. The front left wheel plug is near the fuse box, the front right wheel is to right of the washer fluid box. They are just simple coax connections. Pull them apart and check continuity to the sensor, from the coax to the wall of the plug. Mine read ~1400 ohms, if they are OC then they are bad and require replacing.

As for the pink vacuum pods, see this thread:

w126 vacuum element troubleshooting

4thesporty · #7 10-22-2010, 01:46 PM

Also, just an FYI when your antilock light is on you DO NOT have antilock brakes and your wheels will lock up when braked hard.

RichardLSU · #8 04-08-2011, 12:14 PM

FYI, I just replaced my wheel bearings and rotors. When the hubs were off, I cleaned off the ends of the sensors and put the wheels back on, still having the same problems. It makes me think either one of the sensors is bad or its the rear.

Also, I noticed that the wire from the brake pad sensor (where it attaches to the caliper) to the body was severed. Would this make the ABS light come on?