I went to my local Schuck's dealer and they were able to assist me with pulling some codes.
My print out is as follows...

Trouble Codes:
P170 Fuel Trim Malfunction (Bank 1)

Pending Codes:
P130 O2 Sesor Circuit Malfunction (Bank 1 Sensor 1)

Freeze Codes:
P170 Fuel Trim Malfunction (Bank 1)

Problem: My CE light is on. When the car is stone cold, the car starts rough with idle fluctuating between 1200 & 500 rpms until it warms up (3-5 minutes). After that, the car starts (when warm) and drives without issue(s).

Could it be that I have a bad O2 sensor (since the CAT is cold)? Or would it be the Air Mass Sensor?
Are these both easy DIY?

Oh yea, this is a 2000 C230 w/96K miles.
Thanks!
Shawn

99% of the time code P0 170 on a M111 engine is a bad air mass sensor! MB # 000-094-09-48.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

I had a (sinking) feeling it might be that. Why would it only act up when starting cold vs a warmed engine. Or just because it is warm I don't notice that there still is a problem.

What does a Air Mass Meter do anyway?
Shawn

Controls about 98% of the fuel mixture adjustments!

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Your fuel system has the job of matching the amount of fuel to the amount of air your foot allows into the motor. The air mass meter gives a value for the air flow into the motor and is the most significant of the variables used in the fuel calculation.

Your system adapts using the feedback control (lambda cycle) to correct for mistakes it makes in the fuel calculation. The system is rather amazing as it has about a 30% ability to correct.

What happens is that a bad reading is interpreted and then a calculation is made. It is wrong and the system adapts to add the proper fuel. It does this adaptation at a particular load and then uses it in a multiplicative way to change the mixture in all settings. It then has the further capability to additively correct at idle one more time.

I see AMMs fail lean at load which causes a 1.15 and above multiplicative correction. This means it adds fuel (the limit is 1.32 on the adding side and .68 on the subtracting side). A characteristic of some failures is that they work all right at idle air flow. So because there is a 15% addition of fuel across the board it winds up 15% too rich at idle where it works correctly (an example - not all fail this way). At this point the idle is corrected with the CTP (closed throttle position) additive correction (up to 1ms). This is often what causes the code P0170 and P0173 for cars with a left side.

If you are having a running problem it is because the adaptations aren't working for you. If the adaptations are big and you reset them to zero you can then see how really poor the system would work with the parts as they exist.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

I will order a Air Mass Sensor from Phil on Monday. Thanks guys for the help (DOC) and detailed information(Steve). I now have a better understanding of how this works. After the install, I'll let you all know the outcome.
BTW - will the CE light reset its self at some point? Or will I need a ODB II reader to do this?
Shawn

Trial and error are one diagnostic technique and the downside risk might be small here and it probably nevers hurts to get a new AMM, but the car should be checked for vacuum leaks and the adaptation numbers should be viewed.

After viewing the numbers I will usually readapt to the base line and drive the car a fixed road test of about 4 miles. I then reread the numbers. If large movement is found and their is no evidence of vacuum leaks I then substitute a known good unit , reset the adaptation again to baseline and do the drive again. If the numbers stay put this time I know I have it right.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Steve,
I mostly work or domestic cars but maybe this will work on MBs also. If you unhook the MAS, the computer will detect this and switch to "speed/density" mode which is some sort of limp in mode. I have found this is a good way to determine if the MAS is causing the problem or some other system. Actually, you can disconnect almost any sensor, one at a time, and find the defective one. This helps when the readings are not right but not bad enough to case a Check Engine Light.
Will this trick work on MBs?

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84 500 SEL (307,xxx miles)

I have used that technique on Volvos as they often get in a no start mode with a bad sensor. That has never been the case with MB. I don't know if you would call what Volvo does reverting to speed/density though, as they don't have a MAP sensor but MB will and in a debate I think the controller will default to the MAP.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Well, I changed out the MAS unit the day before yesterday. After the install the car needed to relearn the correct data input from the "new" sensor. Within 20 miles I could tell a differance.

So yesterday after a cold morning start 25 degrees, the car started without hesitation, reved to about 1200+ rpm then down from there (acting like it used to). After, 50 miles and 30+ starts in two days, the CE light went off.

That in my book is a successful DIYer and thanks to stevebfl and M.B. DOC for you assistance.