Hello,

My 1994 c220 vacuum pump has an electrical short, so I have to remove its fuse. I would like to know whether the vacuum system that is controlled by the vacuum pump has anything to do with the other vacuum system that is used for engine management or emission control.

My car recently has shown codes for O2 sensors and MAF (the symtoms are frequent stallings at idle). I have replaced the two O2 sensors and cleaned the MAF's hot-film element with non-chlorinated brake cleaner. After that, no code is shown but the stalling still persists. I'm afraid that the lack of the vacuum pump's vacuum system may play a role?

FYI, the OVP is of the new type and the wiring harness is good.

Thanks a lot for your help.

Best regards,

Eric

I believe the inoperable vacuum pump will have a greater impact on your HVAC operations [if equipped with MVA] if the MVA (manifold vacuum assist) connection has not been blocked or capped. I do not think it would impact engine performance in the manner in which you are describing.

If you can extract the "Actual Values" from the engine managemnt system it may be helpful in identifying a cause to your complaint.

The most significant values would be

• Oxygen sensor readings
• MAF Volume
• HFM Voltage
• Partial Load Adaptation
• Idle Speed Adaptation

I see the message is directed to DOC and Steve..................

What were the codes?? Was the air mass code P0 100 OR was it a fuel trim code P0 170 OR P1 170??

IF the codes were fuel trim then YES having a vacuum leak in the a/c system will have effect on engine codes IF the PSE system pump is inop! IF that is the case then have the A/C vacuum leaks fixed.

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Thanks a lot for your responses.

The codes I received are:

- P0101 Mass or Volume Air Flow Circuit Range/Performance Problem

- P0141 02 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)

- P0170 Fuel Trim Malfunction (Bank 1)


The current symptom is sudden stallings at idle (no hesitating moments). Thanks.

Best regards,

Eric

P0 101 means that you need a mass air sensor! OR that the wiring going to that sensor is defective. Does the engine have a new harness?

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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

Hello M.B.DOC,

Yes, the codes I showed were before replacing both O2 sensors and removing the MAF to clean its thin hot-film element with non-chlorinated brake cleaner. After the replacing them and clearing the codes, the check engine light stays OFF, so it seems that the replacements may be good at least for now. I think it may take more driving around in order for the trouble codes to show up again.

When I monitor the real-time air flow data using the OBD II scanner (autoxray), the number does keep increasing or dropping accordingly based on the engine RPMs (the minimum is 3.33 gm/s at idle), so the MAF seems to work even though it's probably still out of specs after the cleaning.

Since the vacuum pump was dead several weeks before the stalling problem started happening, so I was wondering whether its vacuum system plays a role in this stalling problem. A new MAF is not cheap (about $330).
Thanks.

Best regards,

Eric

MB rebuilt exchange air MAF is 000-094-00-48 & lists for $264.

__________________
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

Dear MrCjames: thanks a lot for your information.

Dear M.B.DOC: your reply is right on the spot!

I have replaced both oxygen sensors and the MAF (AMM), so their codes are gone. However, a new code P1170 has started popping up, just as you said in your first reply.

I don't know much about the door/trunk/A-C vacuum system in this 1994 c220, and don't plan to replace the vacuum pump at this time. Is it possible for me to just use some golf tees to block some vacuum lines so that the fuel trim management is back to normal (i.e. no more P1170 code)? Thank you very much.

Best regards,

Eric

One more question:

What does "PSE" stand for?

Thanks,

Eric

ttt

Pneumatic System Equipment.







.

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Thanks dkveuro.

Eric