I have a 1993 300E 2.8 with 97,000 miles. I recently changed the drive belt at the dealer to reduce engine noise. Since then, on occasions (mostly when the engine is cold), my RPM at idle speed surges up and down ranging between 500 and 750rpm. In addition, I have been having problems with the acceleration. I have to floor the gas pedal and shift gears down to get a decent acceleration and it still takes few seconds before the engine responds. My gas consumption sits at 22 miles per gallon (if this helps). Also, on a couple of occasions, few and far in between, after backing up, when I shift to drive, the engine shuts down. My dealer said that most likely my air pump is bad. It is not pumping the right amount of O2 into the engine ... the cost: $850 for the pump and $100 for labor ... before I go ahead and spend this kind of money ... I would like to make sure that the symptoms are consistent with a bad air pump diagnosis ... could this be due to old spark plugs ... I have not changed them in at least 40K miles ... please help ... this was such a wonderful car to drive ... I miss my responsive engine!

[This message has been edited by George (edited 05-02-2000).]

[This message has been edited by George (edited 05-03-2000).]

I have not seen an air pump cause this. I wonder how the wire harness looks? Have a second opinion on this.

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Benzmac:
Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

AIR pump??? The full name for an AIR pump is "secondary" AIR pump. The reason its "secondary" is because normally it plays no part in the "primary" running of the motor.

The only way I can imagine it would affect running would be if it stayed on all the time and confused the O2 sensor. The AIR pump should shut down after cold running.

Definitely get a second opinion or ask more questions. They have already given a diagnosis, I would ask for an explanation. Remember the secondary AIR pump quits working (when functioning properly) as the engine warms up.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Thanks for the earlier replies ... now that I found a non-dealer shop in the area that was started by ex-Mercedes mechanics, I have a few more observations that I hope you can use to help me understand what I should expect and may be arm me with some questions I should be asking:

1) I have noticed that my fuel economy has been consistently in the 19-20 mpg. I could swear I used to get 26-27 mpg on this car ... is this normal for a '93 300E 2.8 ???

2) I have also noticed oil deposit on the fuel throttle. I could not trace the leak, but the oil deposit covers all of the throttle assembly ...

3) last week, in an attempt to get the car to accelerate, I shifted down to 3rd gear and almost floored the gas pedal and the car was crawling for 5 to 10 seconds and then started to pick-up speed. Also, sometimes when I am driving at 50 to 60 mph and I accelerate, the car starts to accelerate and then I almost feel like something opens up in the engine and the acceleration response shoots up a notch or two.

I read all of these emails about people who changed the fuel pump, the oxygen sensor, the air filter, and so on and so forth but were not able to isolate this problem ... I can really use your advice on what to agree to and what to challenge when I take my car in for service ... thanks in advance!

George.

[This message has been edited by George (edited 05-15-2000).]

I know some people with a 93 300E 2.8 and they get 27 mi/gal on the highway. Good luck!

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Dean
Santa Barbara, CA
1974 280C
1984 300SD

[This message has been edited by dean (edited 05-15-2000).]

George,

I would look at the spark plugs. If they have not been changed for more than 40,000 miles, one or more of them easily could be fowled.

Also, have you replaced the head gasket on this car yet? If not, it is probably leaking at the back of the head on the right side, and from the front of the head on the right side as well. Not that these external leaks would cause this problem, but at 97,000 miles, it is possible that the head gasket is leaking internally as well. Your dealer should, however, be familiar with this problem.

quote:

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Originally posted by dean:
I know some people with a 93 300E 2.8 and they get 27 mi/gal on the highway. Good luck!

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Thanks Dean ... I thought 20 mi/gal was a bit low for this car. This baby is going to the shop next week.


[This message has been edited by George (edited 05-16-2000).]

quote:

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Originally posted by edbardzik:
George,

I would look at the spark plugs. If they have not been changed for more than 40,000 miles, one or more of them easily could be fowled.

Also, have you replaced the head gasket on this car yet? If not, it is probably leaking at the back of the head on the right side, and from the front of the head on the right side as well. Not that these external leaks would cause this problem, but at 97,000 miles, it is possible that the head gasket is leaking internally as well. Your dealer should, however, be familiar with this problem.

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Excellent feedback ... last time I changed the spark plug the odometer was probably at about 50,000 mi. As to the head gasket, I had it changed four months ago ... I suspect I either have a new leak or some oil spilled on the side of the engine as it was being changed. I will get the spark plugs changed, thanks!

Since all this started after work under the hood, has someone checked all the vacuam and electrical connections to ensure that nothing was knocked loose in the course of the other work?

Good luck,

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Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

quote:

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Originally posted by LarryBible:
Since all this started after work under the hood, has someone checked all the vacuam and electrical connections to ensure that nothing was knocked loose in the course of the other work?

Good luck,

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Good suggestion ... I did take a close look at the engine trying to trace the leak, but not fosucing as much on the wiring ... I will take another look today to see if I have a loose connection somewhere.

Thanks,
George.

quote:

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Originally posted by George:

Quote:

Originally posted by LarryBible: Since all this started after work under the hood, has someone checked all the vacuam and electrical connections to ensure that nothing was knocked loose in the course of the other work? Good luck, Good suggestion ... I did take a close look at the engine trying to trace the leak, but not fosucing as much on the wiring ... I will take another look today to see if I have a loose connection somewhere. Thanks, George.

Larry,

You are a genius … I put my detective hat on and looked for a loose connection focusing mainly on the air pump and oxygen sensor assembly. Guess what?? the oxygen sensor connector, the end at the front of the engine on the top right hand side (round connector), was unplugged. I was amazed when I saw it … I connected it back in seconds and voila … no surging of the engine, no acceleration problems and my mileage went back up to 28-29 mi/gallon … I have to tell you it was such a great feeling to find such a simple fixe that within few seconds brought this car back to life … thanks so much for the suggestion … I would never have thought of it myself … simple yet elegant!

Thanks everyone for all your suggestions ... you have been a great help!

George.


[This message has been edited by George (edited 05-20-2000).]

George,
I have a question...You wrote that the dealer said that most likely your airpump was bad. How did he come to that conclusion?
Did you talk to him/her on the phone, or did you go to the dealership? I certainly am not a professional Benz mechanic, but the O2 sensor (was) would have been the first item that I would have examined with a critical eye,...NOT the airpump.
While I am ranting just a little...airpumps usually last a helluva lot longer than O2 sensors. (what I mean is that had I been the service advisor I might have suggested the sensor be replaced...hopefully the next thing that would have happened is that the tech involved in replacing would have noticed the harness being off and said so)

sorry...just venting I guess

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03/83 300D 184k
07/73 280 160k

quote:

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Originally posted by Larry Delor:
George,
I have a question...You wrote that the dealer said that most likely your airpump was bad. How did he come to that conclusion?
Did you talk to him/her on the phone, or did you go to the dealership? I certainly am not a professional Benz mechanic, but the O2 sensor (was) would have been the first item that I would have examined with a critical eye,...NOT the airpump.
While I am ranting just a little...airpumps usually last a helluva lot longer than O2 sensors. (what I mean is that had I been the service advisor I might have suggested the sensor be replaced...hopefully the next thing that would have happened is that the tech involved in replacing would have noticed the harness being off and said so)

sorry...just venting I guess

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Larry,

Here’s what happened … The oil change was due and the engine was a bit too noisy, so I took the car to the dealership to get the oil changed and check out the engine noise. They called me up to tell me that my belts needed changing and they are causing the noise. They went ahead and did the work to the tune of $300 if I remember correctly. I went after hours to pick-up the car, they had a note on the bill saying they found out after they had changed the belts that the noise is coming from the air pump and it needs to be changed. My first reaction was to question whether they really had to change the belts in the first place. Meanwhile since I picked up the car, I started to have the surge problems when I first start the car, the acceleration was down but I had not noticed the low mileage per gallon then yet. In my mind, I attributed these problems to their diagnosis that the air pump is bad … but was curious about the timing of these problems showing up just after I picked up the car …

( On a side note: they had told me as well that I needed to change the tires … a day later the rear right tire blew. When I took the car to a tire shop to replace it, I asked why would a tire rupture as if someone took a knife and separated the side wall from the road wall … he checked the tires to see if they can find anything inside, came back and said they did not find anything, but this kind of a rupture is consistent with having driven on a tire with low pressure for a very long long time … mind you that part of changing the oil at the dealership is to check and adjust the tire pressure!)

Back to the air pump, I stopped by the dealership a couple of days later to pick a key chain or something, and talked to my service manager and the technician who worked on the car at the time to ask about the surge and acceleration problems I was having. The technician remembered the work and said the air pump was noisy and it needs to be changed … and they did not bother to check the oxygen sensor because they believe the air pump is bad. So, I asked them how much was the repair for the air pump, if this will fixe the noise problem, and if they are sure the pump is damaged, etc. … he gave me a total estimate of around $850. Given that I was not convinced they had to change the belts the first time around, and given the amount of money involved, I decided to get a second opinion and I found this web site and the rest is history …

My guess is that they disconnected the cable to do some tests and forgot to connect it back … or if you were a bit less naοve, they were looking to fill their service pipeline …

I hope this answers some of your questions and once a again, thanks for the suggestion to look at the harness … you helped a lot!

Regards,
George.