Idle Control Unit Malfunction.

**martattack** · 10-04-2005, 01:08 PM

Hey guys I've had a P0505 code for a while, but the only thing wrong that I've noticed since then was the lack of Cruise control.

Anyway, so this idle control unit is a spendy little guy, and I'd rather not replace it if I don't have to. I'm thinking of going in and taking it apart and trying to fix the problem myself. I'm pretty mechanically inclined.

I'm just wondering if anyone knows what the most common problem is with them? Is it the wiring that comes out of it? If that's the case, it shouldn't be too difficult of a fix.

**Sulaco** · 10-04-2005, 01:49 PM

What other symptoms are you experiencing? I have the exact same model 202 and I think mine may be dead also.

I get bouncy idle when I first crank it. Rough idle at stop-lights. No cruise control...

And where is this idle control unit?

**martattack** · 10-04-2005, 01:59 PM

Other than the cruise control not working, I'm really not experiencing any other symptoms really.

The idle control unit is actually the throttle body (where the accelerator pedal hooks up to). Apparently it has an electronic actuator that opens and closes the throttle plate.

**Sulaco** · 10-04-2005, 07:40 PM

Oh shit. The TBA.

Yeah, $1,300 for a throttle actuator for our cars. And it's got roughly the same life span as our infamous wiring harness.

There's a guy rebuilding them for $400 though. 6 month warranty I think. He posted a thread in the repairs forum a month or 2 ago.

Saddest thing is ultimately you and I will eventually have to replace them.

**jnenad16** · 10-04-2005, 09:07 PM

there is a throttle body actuator(ie throttle body assembly),and then there is the idle speed module/throttle control module. this is the combination unit. if this is defective, you can get it rebuild for about $200 at
http://store.directauto.com/ I used them many times and they were always able to repair the modules I sent them.

nenad

**martattack** · 10-04-2005, 09:44 PM

Originally posted by jnenad16
there is a throttle body actuator(ie throttle body assembly),and then there is the idle speed module/throttle control module. this is the combination unit. if this is defective, you can get it rebuild for about $200 at
http://store.directauto.com/ I used them many times and they were always able to repair the modules I sent them.

nenad

Thanks for the information.. Now would the P0505 mean that the combination unit is defective? Any idea what goes into the rebuild? Is it just the wiring harness?

Thanks
Martin

**jnenad16** · 10-04-2005, 10:35 PM

do you have the definition for the code?
the rebuild involves them testing the control unit and the different modules/components within. then they replace the faulty ones with new ones. if your wiring harness is intact, there is no need to replace it.
didnt you replace the engine wiring harness not to long ago?

nenad

**martattack** · 10-05-2005, 08:39 AM

Originally posted by jnenad16
do you have the definition for the code?
the rebuild involves them testing the control unit and the different modules/components within. then they replace the faulty ones with new ones. if your wiring harness is intact, there is no need to replace it.
didnt you replace the engine wiring harness not to long ago?

nenad

P0505 Idle control system malfunction

Yes, I did replace my wiring harness, however there is a wiring harness that comes off of the Electronic Actuator which isn't replaced with the Main wiring harness. See here:

#65

Thanks again.
Martin

**Sulaco** · 10-05-2005, 09:32 AM

Yes, if you look at the m104 DIY harness replacement on mercedesshop.com he had to replace his TBA (#65 on your diagram) as well as with his wiring harness. He shows a pic of the harness going into the TBA and it was completely decayed and ruined.

**martattack** · 10-05-2005, 10:38 AM

I think I found something of interest.. It looks like it's specific to the V12, but I am probably going to try this on my TBA

http://v12uberalles.com/throttle_actuator_rewire.htm

**Sulaco** · 10-05-2005, 02:40 PM

That looks doable. Now I just need to solder!

I think the part is the same on all cars, seeing as how identical that one looks to our's (on the outside at least).

**dono** · 10-05-2005, 03:47 PM

My thanks to all of you on your valuable inputs. Just an FYI; My 97 C36 has had a rough to low idle since I bought it. and occasionally the idle speed seems to surge high and low upon start up. otherwise it runs great.

Regards,

dono.

**Sulaco** · 10-05-2005, 07:10 PM

Same here (idle issues). Even though everything seems to be in perfect working order. Most certainly traced to wiring harness and TBA.

**dono** · 10-06-2005, 03:13 AM

When I changed my plugs, the engine harness looked okay. from what I can see, the small harness going to the TBA looks okay as well. from what I have been reading, I believe that MB stopped using the problem prone wiring in 1996. if this is true, I would think that my problem is limited to the TBA itself.

**martattack** · 10-06-2005, 09:36 AM

Originally posted by dono
When I changed my plugs, the engine harness looked okay. from what I can see, the small harness going to the TBA looks okay as well. from what I have been reading, I believe that MB stopped using the problem prone wiring in 1996. if this is true, I would think that my problem is limited to the TBA itself.

You are correct about the wiring harness. However I'm not positive if the TBA wiring remained prone to failure in 1996+.

Your symtoms that you listed above could very well be the TBA, but it could also be your MAF or even your oxygen sensor.

DOes your Cruise control work?

Martin

**dono** · 10-06-2005, 11:44 AM

Cruise control works. My MAS was changed by the guy that I bought the car from a few months before I took possession. (I found the receipt in the glove box). By the way I just came back from the benz dealership, and with my discount the TBA as shown in the diagram above is 460.00
bucks. Once I am certain that is the culprit, and it really starts to fail I will swap it out. Today it has been Idling okay.

**Sulaco** · 10-06-2005, 12:10 PM

Omfg. $460 for a TBA from the DEALERSHIP. That's a $2,000 part! Even importec lists it for $1,300. Rebuilt ones will cost you $400.

That's an INSANE deal. God, how do you get that kind of discount?

The dealership should at LEAST give all us m104 owners a huge discount on wiring harness, TBA's, and head gasket jobs. Seeing as how they refuse to recall even though the 3 issues are most certainly worthy of a recall.

I fixed my voltage regulator and fixed alot of electrical problems but I'm afraid the 16v running from the alternator might have sent some of my old wiring over the brink. It's now having rough idle issues that it didn't have before the voltage went bad. I'm afraid it's pushed my TBA closer to death

But it ONLY has a rough, missfiring idle when the A/C is on...

**dono** · 10-06-2005, 12:15 PM

He double checked it and he printed out the exact drawing shown on rhis thread. he did comment that the pricing has come down, and it does vary per model. the list is 563.00.

**Sulaco** · 10-07-2005, 08:20 AM

I'm going to call my local dealership. This is crazy.

**benzaddict** · 10-07-2005, 12:32 PM

You guys need to remember that his 1997 C36 has a different fuel inhection system (ME-SFI) than you 1994 C280's (HFM-SFI). His throttle actuator is much smaller and way cheaper than yours. You're comparing apples to oranges.

Boominbenz, you can try to rewire yours, I've tried a few times in the past, but honestly haven't had the best success. Good luck, give me an email if you have any questions.

**martattack** · 10-07-2005, 12:50 PM

Originally posted by benzaddict
Boominbenz, you can try to rewire yours, I've tried a few times in the past, but honestly haven't had the best success. Good luck, give me an email if you have any questions.

Is it typically the wiring that is the problem? Or is it something else like a potentiometer?

Thanks
Martin

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