My friend with the 1990 300SE has erratic idle when in gear. Sometimes the idle will go up and down and sometimes require harder braking when it idles up. Anyone know what causes this?

Bad P/N switch? Sticking ICV?

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.

Thanks. Whats a P/N switch?

Park/Neutral... Lets the engine know it's in gear.

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.

My bet is on the airflow potentiometer. There are a few people who sell them on eBay and here are the instructions to adjust it. I had the exact same issue and that fixed it for me.

http://sg-motorsports.com/AFS%20Pot%20write-up.htm

Any updates? Did you replace the injector seals?

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1991 300E - 212K and rising fast...

I too have a similar problem with my '89 300CE. The slightly rough idle is definitely noticeable. So far the fuel pressure regulator, injectors+seals, fuel filter, new Beru wires, and new Bosch plugs have been installed. I also visually inspected the cap and rotor which were both in good condition. The dealer sold me new Bosch Copper plugs (HR9DC) as I can't find the original H9DCOs anywhere. It appears that stock has run out of the originals.

The NKG platinums I pulled out were in excellent condition, no fouling or any other indicator to a poorly running engine. Just out of curiosity, I've noticed that the economy gauge tends to sit off the peg and inch towards the red area at idle. I can see it fluctuate slightly at times. The tach also moves up and down ever so slightly as the engine surges lightly. When I put the car into gear, such as reverse or a drive gear, the fuel economy gauge moves well out of the black area and towards the right. Is it normal for it to do this when the engine is put under load, even when no throttle is being applied?

No sorry. I've been bad about it honestly... Been living with it and putting money into my track car instead. And there are two W203s in the household that are constantly giving me problems too.

It's a small issue to live with now. Maybe over the Christmas break I may attack it.

103: Correct spark plugs and a cleanliness of ignition system are vital.
Over a period of time the spark plug connectors develop a conductive leakage grounding to the metal cover shroud . A good cleanup of the connectors rectifies the slight shivers the engine develops.
in these models .
mak

Thanks. Well I have the car for sale, but I want to perhaps change the plugs. As mentioned in my ad, my car has the slight "pulsation" occasionally on light and steady acceleration. Its like I am gently "working" the pedal when I am actually holding it steady.

So, I wonder if that could be the plugs or that airflow potentiometer that chowbow mentions? Seems easy enough, but I am not comfortable with working with fuel lines (and the instructions say a fuel line has to be removed), but I would like to get it fixed. Maybe a local MB mechanic can do it.... or the new owner?

Mine has a little hitch that I have asked about in the past. I live with it..and have for 7 years or so. Had a dealer switch out my fuel distributor with one from a 2.6 190E. Told me the problem was cured, but I would need a new fuel didstributor. Wasn't solved and I'm still running with the swapped out FD. Seven years later.

FYI....

Just Bought 1988 300CE... Few questions-Any Thoughts???

M103 W124 raise idle by 50 rpm

I have found that just switching the plugs is not enough..if the car has been running with incorrect plugs over any extended period...you will likely need to go back and change the dist. cap. rotor and plug wires, as well as the plugs...even if all those items were new at the time of installing the incorrect plugs. The problems you are seeing are not necessarily from a deterioration of the incorrect plugs themselves, but from the damage they seem to effect on the whole ignition system. The effects seem cumulative..and since you said the car ran corrrectly for 12,000 miles before showing symptoms, I suggest you follow the procedure. Try to use "OEM" for everything else other than the plugs unless they are the correct copper non R versions.

I solved multiple issues on my 2.6 (w201) including the hard starting, idle shudder, periodic runaway idle (up to 3000 rpms occasionally), poor gas mileage, stalling when coming back to idle, simply by executing the procedure above. These symptoms did not all happen at once but progressivly got worse and more extensive over time. The change was as dramatic as flipping on a light switch.

I say use MB as a source, because aftermarket Bosch stuff comes from all kinds of different sources..which are not necessarily equal. I cannot tell you how many different versions of what should be the same parts I have recieved as after market supplied "OEM" Bosch.

Found the problem... it was so simple.

While I was messing around with my steering box adjustment, I noticed some fuel smell. The car had been off for about 10 minutes and I thought it was strange to smell fuel as I was messing around there.

Turns out that the fuel line that supplies fuel to the fuel distributor, was seeping. There is a rubber hose that connects to a metal pipe, which connects to the fuel distributor. At the union of the rubber hose and metal pipe, was where it was seeping. It looks like the hose is glued on or something. But all I did was put a hose clamp on it, and all is well. 5 cent fix.

Nice! My shuddering idle was traced to O2 sensor.

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1991 300E - 212K and rising fast...

o2 sensor is probably the deal on mine. The check engine light comes on for about 30 seconds after its started, then it goes off. Its been doing this since I have owned it.

How to do read the CEL code on a 88 Mercedes?