one thing they also said was that if one accelerates the car slowly, there is no problem, only when one accelerates strongly does it stumble.

Does this sound like the air flow meter or the fuel distributor like the previous tech thought it was?

a new coil should not make it worse. Also the airflow meter is $40-80 cause all you really need is the potentiometer from bosch. I would do a search on the potentiometer cause some one found it for less than I paid for mine. The actual flow mechanism is pretty darn reliable so I doubt very much it is that, rather just the potentiometer. This stumble used to be really common on the old 450 engines and they would also stumble around 55-60 to. God I miss that engine it was so simple.

__________________
Martin Ingram
Colorado Springs
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)

Thanks. So the $1,000 air flow meter never goes bad? Isn't the AFM different from the potentiometer?

Apparently the new coil lessened the performance for they are putting back the old one. Maybe the new coil is bringing on whatever the problem is even worse. Amazing how much time and money I am spending on this little stumble.

by the way, what does the symptoms from the last couple threads indicate? Essentially, idle OK, but poor performance when accelerate hard.

Before the idles was crummy and accelerated was consistent - poor for the frist 10 mph.

"So the $1,000 air flow meter never goes bad? Isn't the AFM different from the potentiometer?"

Actually, the potentiometer is the one that goes bad in the AFM.
(the pot is part of the AFM)
In the past you had to buy the whole thing (1k bucks), now you can purchase the pot separately (for 40 bucks plus shipping), and attach it to your AFM assembly.

__________________
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
609 Certified

Yup the afm is a larger mechanical unit with a piece of plastic scewed into it (the potentiometer) this is the thing that breaks. MB only sells the whole unit unfortunately, but you can by the potentiometer seperately now.
m

__________________
Martin Ingram
Colorado Springs
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)

Just drove the car. It is worse than before (now it has poor idle and acceleration), but they said the poor idle may be due to putting on a bad set of new wires. They will put on another new set tomorrow. They said that the acceleration is probably due to a faulty air flow meter.

They told me that you have to buy the whole air flow meter from Mercedes, not just the potentiometer. Are you sure you can get an official Mercedes potentiometer separately?

So tomorrow, a 3rd set of wires and then discussion of the Air Flow Meter subject.

Can the potentiometer be bought from a Mercedes dealer separate? If not, where to get it separately?

Is this the potentiometer from one of pesuazo's previous posts? I found one for $41 on a eurodirect.com, but will that fit on my 89 420 sel? Are they all the same?
Can I get the potentiometer without the air flow meter from the dealer?


Is the potentiometer the part pictured at this link?

Sudden surge when decelerating.

Is this the same one for my '89?

After one week in the 2nd shop, the car runs worse. It now idles really bad at idle, stalls when you give it gas more than gently, and won't start unless one pumps the pedal. Essentially all they did is put on new fuel pumps and a coil, another set of wires, and then replaced them with the other ones since it did not make a difference. The put on a new fuel filter, which they said did not look good, but said the car ran even worse after that. Will keep you updated.

Matt, the potentiometer can be bought seperately. Prices from $40-80. the picture does show the correct part. The part number is in my thread you found. I really do not think it is the pot. However, I am still think you have an ignition issue. However, it would be nice if we could see the eha and dutycycle numbers too. This may help confirm the problem is fuel or ignition.
m

__________________
Martin Ingram
Colorado Springs
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)

mattsuzie:
Yes, that is the pot.
To make sure, you can read the part number right off the pot itself.
No, the dealer does not carry the pot by itself.
The old version ended in 015, the redesigned ends in 035.
You are correct, Eurodirect has it really cheap (42 including shipping).

I thought joe p was going to work on your car?

__________________
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
609 Certified

Thanks Gentlemen. I will let you know what the culprit is.

So far I talked to 2 Techs and the dealer. No one will just put in the potentiometer, have to put in the full air flow meter if to repair unless I do it myself.


I will let you know what the culprit is.

That does not surprise me, luckily it is a very easy job.
m

__________________
Martin Ingram
Colorado Springs
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)

I would take the risk of installing the pot myself ($42), rather than pay $1K for the whole unit "to see if it fixes the problem".

By your description the techs are just throwing parts at the problem, with no success.
New wires (3 times), new fuel pumps, new coil, new fuel filter, now new AFM?
Proffesional mechanics are supposed to diagnose and repair, not throw parts at it at your expense.

You and I can do stuff like that.

If you do not feel comfortable changing the pot, perhaps we can meet a weekend and work on our cars together (may be 87-300E_in_NC will join us, his mechanical skills are excellent). He has a spare pot, which we can test. Or may be swap pots from our cars.

Just let me know.

__________________
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
609 Certified