jayitx

Hey everyone,

It's been pretty cold here in Texas the past few days (20s during the day, teens at night). Not extreme, but cold for Texas. My car had been sitting for a few days without starting it, and I needed to go to the grocery store Friday night. I drove it about 1/2 mile to the store, went i, came out and started it again, and it was idling VERY rough. I couldn't even give it gas to go - it just shook and stuttered. I shut it off and restarted and was able to get home, but the rough idle was still there. I got a code reader last night and checked it out today. The rough idle is still there, but only at idle. When it's warming up over 10k RPM, it's smooth. As soon as it kicks down to idle, it starts shaking and stuttering again, then stalls. No problems starting it, just idling. The code I get is P0105 Manifold Absolute Pressure/BARO Circuit. I did a search and found a little information, but I want to ask everyone for advice. Is there a common problem with the C32 that could cause this one? One thing I found during a search was a possible vacuum hose leak, which I need to search for. I can see a hose freezing up and cracking after a few days. I also saw a possible MAF sensor. Anything else I should check? I have Magnecor wires, Johnson pump, SL55 full intake, K&N filters, and ASP pulleys. No problems before this happened.

Thanks for any suggestions anyone can give me!

Dingleberry

i have no idea what i'm talking about...

with that said, it appears that your MAP sensor might be fried

Lenin

I agree.
How many miles do you have on your car and have you tried clearing this code? Is this the only code that you have?
I have seen P0105 come up at the track when the boost goes above 22 PSI. Also since it's an electronic component, it is possible that it just gave up after the resent temp. drop.
BTW, our cars don't have a MAF sensor.

jayitx

Thanks for the responses. I have about 104k miles on it, and it's the only code I got. I tried resetting the throttle, but it's still the same. I realize we don't have a MAF sensor, it's an MAP. I guess I typed it wrong.... I broke my right hand last week and had some pins put in this week, so typing anything is a real chore since I'm right-handed. I was hoping to get some suggestions of easy-to-check areas from the forum. I don't see any obvious broken hoses. I've been looking up the location of the MAP sensor and it's something that I know I could do myself, if I have 2 hands. I got a deal on a complete car cleaning from my Mercedes dealer a few months ago, when I paid them for Service A - $99.00 interior/engine clean for $9.00. The engine looked brand-new afterwards, except for the area where the IAT and MAP sensors are located. All the dirt and grime ended up there, so that may be the cause of a bad sensor.

I'll wait 4 weeks until the cast comes off, and drive my wife's A4 until then.

Any other suggestions or opinions are greatly appreciated.

jayitx

Does it make sense that the idle is smooth in Drive, Neutral, and Reverse? There's only a problem when idling in Park.

Lenin

First, I hope you feel better and your arm gets back to normal.
I don't know if the above condition is normal but I can tell you that my RPMs changes when I shift from Drive to Park with the Park having higher RPMs. So, there is a different map in the ECU for Park vs. Drive.
See if you can wiggle the wiring harness? Play with the wires that connect to the TB and MAP. It's hard to recommend anything until you eliminate the MAP sensor by replacing it. It's a good idea to replace it anyway with your mileage. It's under $60 on parts.com. You can replace it without removing the SC. But you do need two hands. The good thing is that you don't have any other codes (like P0301-P0306).

jayitx

Thanks. It's pretty frustrating to type, and I have to learn to do everything left-handed.

Anyway, thanks for the info. It makes sense that there's a higher rev through the gears. Any idea what the part number is from parts.com?

Robert AMG

iTrader: (1)

A005 153 72 28

jayitx

Thanks!!

Lenin

Yep. That's the new part number.
Rob, didn't you also have your share of problems with the MAP sensor?

Also, what I earlier described as the P0105 behavior on the track is actually a P0108 code. Overboost.

Robert AMG

iTrader: (1)

i still have the pressure sensor code short circuit to positive, i am reaching 22psi at redline fourth gear but no overboost code.

francoisisp

I tried to find this part number ( A005 153 72 28) on parts.com and couldnt find it, anyone knows where to get them ? or how much it cost at the dealership ?

Robert AMG

iTrader: (1)

you'll find it on parts.com but don't put the letter A at the begining.

jayitx

I just sent them an email to verify the part number. I'm also asking about the air temp sensor and CPS.

Robert AMG

iTrader: (1)

AIT = 000542 28 18

jayitx

Well, no luck yet fixing this problem. I ordered the MAP sensor from parts.com and took everything apart (with basically 1 hand!). Replaced the MAP sensor, removed the lower y-tube and cleaned it up, and replaced the air temp sensor while I was at it. Everything in that area looked fine from what I could see. I put everything back, and used the Needswings cork gaskets for the manifolds. Started it up, and it still has the same problem. I tried 4 or 5 more times to make sure, and I'm still getting the P0105 code with a really rough engine idle. Just for the heck of it, I tried reseating the Magnecor wires, I tried starting it without the air boxes to see if that had any affect.....nothing. Now I'm really stuck!

What could have gone wrong or died "just like that"? One minute the car is running fine, I get out and go into the store, then start it up again and it's junk. Does anyone have any other ideas?

SilverBulletAMG

Wish mine was smooth at 10k RPM.

MountainStone

I hate going through the trouble to replace a part only to discover it doesn't fix the problem. You said in a earlier post of this thread that you have a code reader; after replacing the MAP sensor does it still have the MAP code?
If so I would guess a problem with a connector or wire.
If not I would suspect a vacuum leak, except I can't explain why the symptom of a rough idle is not consistent (only in Park and not in D,R or N).

I have seen the old trick of checking for a vacuum leak by spraying short squirts of ether around the hoses that hold vacuum; if you spray a short blast of ether close to a leaking hose, the engine will ingest the ether and the idle will increase momentarily.

Good luck, and post your results!

EDIT: I have read a couple 'rough idle' threads here that were caused by accidentally switching the two plug wires on one cylinder. Double-check to ensure all your plug wires are connected to the correct spark plugs.

jayitx

Yup.....still getting the P0105 code. Th plug wires are correct, and the car was running fine until all of a sudden this happened. I would think that if it was wires or plugs, I'd get a misfire code with the reader, but I'm not. There's only 1 code too, not several.

I guess I'll try putting the OEM wires back on and check the plugs too, since I have no idea what else to try. I'm thinking there's a vacuum leak somewhere.

Does anyone have a drawing of all the vacuum lines in the C32, so I can check them 1 by 1? I would greatly appreciate it.

jayitx

When I replaced the MAP sensor, I was surprised to find that it did not connect to a piece of tubing. Instead, it drops into a hole and has an o-ring around it to seal it in place. I have to assume that there is some type of tubing on the other side of that hole, correct? I've never seen inside that area, so I'm guessing. Is there any way to check that, or would I need to disassemble the whole engine?

Gramma_Benz

Try this:

With the car off and the key out, Unplug the cable going to the throttle body, it's right on top. Wait one minute.

Plug it back in, put in your key, turn to position two and wait one minute.

Start your car.

Hope it works!

Lenin

The MAP sensor does not connect to any tubing. What you found is correct. This is an electronic device.
As others have suggested check the wiring harness that goes to the TB. Make sure the contacts are clean. You may also need to clean the TB. There are instructions for it somewhere. Just be very careful. A vacuum leak can also be a problem but you said that you checked all the houses.
You have some kind of a initialization check failure. Then at higher RPMs, things go back to normal.

jayitx

Thanks for the reply. Just so I understand correctly, do you mean the cable that connects to the top of part #8 in the attached image? I did remove the entire part and replaced the gasket, so I did disconnect that cable. But I didn't turn the key to position 2 and wait for 1 minute, so I'll give it a shot.

02C32guy

Something that caused me idle issues was a little black vacuum hose behind the right air box. When I installed my SL55 intake the bigger air boxes pushed the hose apart. As soon as I reconnected it things went back to normal. I know you said you checked all of the hoses, but so did I and I missed that one. You need to remove the right (driver's side) air box to get at it. My symptoms weren't exactly the same as yours, but it's worth a look. Also, I don't know if it would throw a code, but is it possible that it could be water in the fuel? I used to have that problem all the time with my old C280. Gas dryer took care of it. Again, just a thought.

jayitx

OK, I tried disconnecting the TB cable for 1 minute, then putting the key in position 2 for 1 minute. The car started and ran just fine! I shut it off, waited a few seconds, and tried again.....same problem - P0105, rough idle, etc. I disconnected all the hard, yellowish tubing that runs underneath the supercharger and blew air through each one, put it all back and still had the same problem when starting. I tried the TB cable again, but no luck. I decided to look at other unrelated thing in my car for a while, and after about 15 minutes, I gave it another shot. This time the car started with no problems. I revved the engine a few times and let it run for a few minutes. I shut it off and started it again. Again, it started fine. I let it run for another few minutes while I put the air boxes back on. I've started it about 10 times since, and it works fine, although sometimes I hear a high-pitched chirping sound when I shut it off, which was never there before.

So it seems to be running again, for now (thanks Gramma_Benz!). I cleared the code, and it hasn't come back yet. I'll keep a close eye on this one for a while.

Any ideas what the high-pitched chirp sound could be? I happens just as the engine shuts off.