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Old 08-30-2000, 06:58 AM
Posts: n/a

I've a '90 300se. Recently when I stop the car the engine shudders a bit and then dies. The RPM meter toggles for a while and the engine shakes before it dies. While driving the car is ok. I have resorted to leaving my foot on the accelerator pedal slightly when the car is stationary. My mechanic initially changed the fuel pump and filter but this did not solve the problem. He tells me now that the "fuel seperator" needs to be changed. What is this and do you happen to know how much it would cost?

Thanks a lot.

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Old 08-30-2000, 08:22 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Actually, I don't know what he is talking about. The evaporative emission systems have a vapor separator designed into the tank on most cars. They used to be separate.

I read a lot of posts asking questions, where previous parts were installed. It seems that there must be a lot of trial and error testing going on. It would be my position that any part being installed would solve some specific test deficiency. This is proper testing. If you think a fuel pump is failing at idle (the most unlikeliest senario I can think of) it would more likely be electrical (relay etc).

The hypothesis should be backed by fuel pressure test readings which then are verified upon replacement. Believe me, whatever is occuring has a result that can be measured by more than the seat of your pants (the seat of your pants said the car died).

I personally would go for an OVP relay if I was shot-gunning parts. The test that would prove it would start with measuring the current through the idle control motor. Low idle that stalls the car will get readings below 500ma with 600+ being appropriate. The OVP relay causes the low idle by providing a weak circuit that reduces the current even with the controller trying its hardest.

Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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Old 08-31-2000, 01:37 PM
Posts: n/a
Hi Steve,

Thanks for the advice. My mechanic has replaced the OVP relay with a similar one from another car. Still did not solve the problem. I'm getting him to show me the part he'll be replacing and will let you know more. Spent $ 400 replacing the fuel pump and filter.

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Old 08-31-2000, 05:51 PM
engatwork's Avatar
Join Date: May 2000
Location: Soperton, Ga. USA
Posts: 11,232
I had the same type of thing happen on a Mazda MPV that I had. Replaced the idle speed control device on the intake manifold and it solved the problem. In an emergency you can rap on it with a small (17 mm) wrench and it will return to normal operation.
good luck
'95 E320
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Old 08-31-2000, 07:48 PM
Posts: n/a
It sounds to me that the ignition module in your distributor is knackered (providing these cars have an ignition module).

My girlfriends 87 ford laser had the same problem being that it would stall at low revs when going round corners or at intersections. The replacement for the laser was about $120 (Australian) and it was a simple job. Remove distributor cap, replace module, replace distributor cap.

Hope this is of some help.


84 300GD
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Old 08-31-2000, 09:20 PM
Registered User
Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
Be careful, you can chase this for a long time. I have seen this caused by no less than 6 different things.

Have a proper diagnosis done and all will save money.

Donnie Drummonds
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Old 09-01-2000, 08:07 AM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
Read many posts on air flow sensor as this part is crutial to "coast" idle stability durning decel.
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