It has a LH-SFI (hot wire) closed loop system controlling Lamba. See MENU#4 for how-it-works. There's no adjustment that I know of . . .

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Regards . . . . JimF
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'94 S500 Cpe

Visit my Mercedes Web Page

No Hot Wire on that chassis.
They are HFM/SFI.

ill look but if I remember right the potentimeter cant be adjusted on hfm systems. Its an electrical device. The only thing you can adjust is the mixture and a few other things. You could try cleaning the fuel injectors and replacing the air filter to start addressing the gas problem. How many miles to the gallon are you supposed to get on the highway and city?
I know mercedes arent known for good gas mileage. Think one of the s class gets like 10 to 15 miles to the gallon.

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

I changed all that already. the idle stays steady, about 800 on drive, and 1200 on park. im only getting like 13 miles per gallon now.
i think its running too rich.

You gotta a lambda tester? You are going to need a need lambda tester to see what the percantage is. 50% is nothing wrong, anything lower or higher than that means you got problems. check your spark plugs and see what color they are. If they are black then its running rich.

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

and what do i do if its running rich?

Check the Purge Switchover Valve (Y58/1) on the left side of engine compartment close to ABS unit.
Check EGR valve also if you got one European cars does not have EGR valve,

ok will do, i know how to check the egr, but the purge switch over valve, im not sure how to check it.
thanks

I would just use a lambda tester and see what perctange its at. You need to get the car up to operating temperature and measure the perctange. I wouldnt replace this part or that part until you get a lambda read out. You could be wasting money and replacing parts you dont need to.

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

The first check for rich condition on 104 w/HFM is fuel pressure regulator.
They are a common fault item for leaking.
Take the vac lline OFF and look/smell for fuel in the line ..There should be NONE.
If there is , replace the regulator.
What happens w/bad reg. is un-metered fuel gets sucked into the engine intake through the vac line of the regulator..............
That will effect BOTH fuel/air mixture and idle speed.
This test takes 4.9 nano secs. to do, so that is why it should be First Check

i checked the fuel pressure reg air line, and i did smell gas in there.
one thing i have been noticing is that when i first start it, the idle is low, about 600, then a few seconds later, it goes up.
but it does stay low for a bit.

how do u change that by the way, does it just pull out?
thanks

to change the fuel pressure regulator make all disconnects and it should come out.

__________________
1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

Do you know there is all this info in the Archieves and this site has an excellent Search Feature with an extensive Library ?

Sometimes I back off to answer b/c I know after I send you in the right direction , I am going to get back 5 questions like "Where is that?? " or "
"What does it look like ?"
Use that search engine. ..this simple stuff all been covered here a zillion times.

I removed the fuel pressure regulator.
I didnt release any pressure before i took it out, so when i took the pin out, it shot right out with a bang, im not sure if there was just too much pressure in there. specially when the car was off for a few hours.

i put air pressure in from the bottom, and nothing came out where the vacuum line connects.

does it seem like its bad?
thanks