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Old 04-18-2003, 11:57 PM
zorin's Avatar
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Join Date: Feb 2003
Location: Ottawa, Canada
Posts: 126

Does your car have the diagnostic port? If so measuring the voltage on pin 3 can reveal alot.

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Old 04-19-2003, 11:01 AM
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Join Date: Jan 2002
Location: England
Posts: 1,841
So.... (sorry to do this) now that you're an expert maybe you can help me with something my car has done ever since I've had it but I never bothered to sort out...!

When cold, it idles very low, almost as if it's going to stall, and when you start it you need gas to get it going. Then if you let off too quickly it will stall. It's fine when warm (though idle is not 100% smooth), and it's adjusted fine (as done on computerised emmisions test). Other 4-cyl MBs seem to automatically have a higher idle when cold, but not mine. Where do you think I should start?


2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black 2nd owner
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Old 04-19-2003, 12:36 PM
pmizell's Avatar
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Join Date: Jun 2001
Location: Houston, Texas
Posts: 838
I have somewhat of a similar problem as pento

My 300E usually starts the first time when cold, will bumble and stumble for a moment then catch and rev up to about 1k during the cold start enrichment. Thing is, if I hit the pedal even the slightest bit during this time, the engine dies immediately. Strangely enough, this all goes away once engine moves past the 60c temp mark.

Fuel economy is horrible -- somewhere around 16-17 mpg and warm starts are a little more difficult (not too bad) usually taking around 5-7 seconds of cranking, where before it'd fire right up. I'll be doing some fuel testing this week when my gauge arrives but if anything immediately comes to mind to anyone please let me know.

'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi
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Old 04-19-2003, 08:41 PM
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Join Date: Oct 2002
Location: Toronto, Canada
Posts: 700
sorry for the delay :)

Sorry guys I haven't checked this thread lately.

Yes, I figured out what was causing the hesitation. For some bizzare reason the O2 plug got messed up and the voltage fro the heater was jumping to the sensor wire and giving the ECU a reading 3X as hight and because of that the ECU would not allow any further enrichment, so this is why the car hesitated. I unpluged the heater and the problem is gone, I still have to fix up those wires.

As for the low idle, I would check the idle control valve, I had a weird idle too but I cleaned it with some carb cleaner and it fixed a lot of problems. If the car dies when you step on the gas, there might be a problem with the temperature sensor, perhaps it gives wrong data to the ignition computer and goes into the right readings once it heats up, it's probably not it but it could be, I would also check the mixture. From my experiance, the mixture, as thought by many to control the idle, has the side effect of changing the idle, but it is not supposed to be used to do this. If all your sensors that are used for mixture adjustment are correct, hook up a multimeter to the EHA, and when the car warms up see if it goes where it's supposed to, early models 8ma, later models 0ma, if it does, then your mixture is fine and the problem should be found else where.

Now, also very important, this is something I did not want to believe at first, but the ignition components are EXTREMELY IMPORTANT. Good spark plugs, wires, rotor cup and distributor, the rest are either 100% fine or dead, so no need to worry there. Basically think of it this way. the Ignition computer sends out a signal to ignite a cylidner four times every cycle, for four cylinder engines. This has to be done with the greatest precision because if it's not, the next ignition will be off, NOT because of the computer but because of the pistion position, this will then upset the next spark, and so on, the only reason that the engine still works is because it happens so quick that there is actually room for error there, but not if you want performance and a smooth idle. Even when one cylnder misses, the engine has still enough force to skip that one turn, I'm not sure how many cylidners you can shut off until the engine refuses to run, and I'm not going to find out using my engine either.

This I know for a fact, I was able to get a perfectly stable idle and smooth engine rpm incrase with an 18 year old car, and blieve me, my car was abused beyond anyones belief, so you can do it too, and of course I will do my best to help.


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