rough and stumble - 300E

i have an 89 300E that just won't seem to idle at the correct RPMs while in "D". RPMs are fine in "P" however it seems to have a bit of stumble and
shake action. i have just changed all the injectors, they were very dirty and may never have been changed. Pervious owner must have been very lax in maintenance department. I also replaced the O2 sensor which also appeared to be the original issue. The lambda setting has been adjusted to the correct value range. But it just won't come up to the 6500 RPM, sits just above 5000.
My 86 seems to have developed a similar problem too.
any ideas?
thanks
iain 86 300E 89 300E
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you say maintenance has been skipped in the past: so what about HT leads - plugs - distributor cap - rotor arm?

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thanks for the responses.
i didn't mention that the plugs and mounts have been changed too. i'll look at the distributor, rotor, idle valve. i'm not sure what "HT leads" are?
iain

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HT (High Tension) leads connect each spark plug to the distributor. they may be called something different if you are in US or wherever (i'm in UK, that's what we call em here)

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Have you ever discovered the problem?

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Well the problem continues........
Repairs to date are, new distributor cap, old one showed possible burn marks at the connectors and may have had a hairline crack. HT leads have been checked for resistance both hot and cold and all are in good condition. And new injectors, mounts, O2 sensor and plugs. Lambda reading is now pretty constant, fluctuated before cap changed.
The Problem: In Park the tachometer reads OK at approx 650rpm as per the spec. At this point there is some minor stumbling but could be ignored by some, but it's starting to drive me nuts so I can't ignore it. I have noticed that the fuel consumption gage reads up about 10-15% from minimum while in idle. If I bring the RPMs up to 1000 then gage drops back to minimum. This also tends to eliminate the stumble problem. If the fuel gage is monitored the stumble coincides with a rise in the fuel consumption gage to as much as 25%.
When the car is put in drive the RPMs drop to about 500 and the stumble becomes more pronounced. Take off will sometimes be delayed or at times the car will stall when I give it gas. Also the fuel gage goes way up before it stalls so I take that as a warning and if I back off on the gas the problem will some times clear before the engine kicks out. This is dangerous in intersections as you might imagine.
The stall will often happen too when switching from reverse to drive, especially on an incline.
I have also observed that the problem usually comes up after the engine has come up to normal running temperature. On this car 80 on highway 90 in city on the temp gage. When engine is cold car works better.
The mechanic who works on the car seems not to be figuring this one out either and I'm sure he's doing his best. He isn't a dealer though and does not have all the diagnostic gear.
Thanks
iain
On 10/5/03 10:12 AM, in article gFVfb.71079$ snipped-for-privacy@twister.tampabay.rr.com, "Victor"

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It appears to me that your engine's air / fuel ratio is too lean for it to run smoothly.
The clues are:
1. problem occurs after the engine is warm - no cold start fuel enrichment.
2. stumble when the throttle is opened, especially when suddenly opened wide.
3. ignition system has been checked and / or replaced.
4. misfire at idle.
A vacuum leak into the manifold via a cracked or broken vacuum hose will cause such problems at idle and low speeds but NOT affect acceleration so much.
An gas engine needs about 1 part fuel to 14 parts air to run well at a constant speed but 1 to 11 to accelerate -get the picture? Something is preventing your engine from being properly fueled.
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Thanks for the response.
I spoke with the mechanic and he says he checked for vacuum leaks already and it came up fine. Any other ideas greatly appreciated.
Thanks
iain
On 11/20/03 9:27 PM, in article snipped-for-privacy@NoHamOrSpamcomcast.net,

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A shop with a hydrocarbon tester should adjust the fuel injection air / fuel ratio to specification - now appears to be too lean.
Your current mechanic isn't much of a mechanic if he didn't do this already - but then selling you replacement parts from time to time is more profitable than making a one time adjustment to fix the problem, especially when that can be done as your patience wanes and Eureka! the problem is fixed and you're happy - despite the donnybrook that it took to get there.
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Thanks again for the response.
The mechanic does have the tool to measure air/fuel mixture and it has been adjusted to to spec. This was the first thing he checked and it was out of spec at that time. I don't think he's trying to hose me at all as he's done work on the car from time to time and not billed me for it.
Thanks again
iain
in article snipped-for-privacy@NoHamOrSpamcomcast.net, T.G. Lambach at snipped-for-privacy@NoHamOrSpamcomcast.net wrote on 11/21/03 5:46 PM:

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i would change the temp sender as it may be giving the computer the wrong reading. causing it to send the wrong single at times
case
the case, minus a few cans!
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What year is your car?, for now I assume you have a 300E between 1986 and 1989, because what I will tell you only covers these years. Readin your posts, I can tell that your mechanic isn't out to hose you, sounds to me he is pretty frostrated with the problem. Has he done the following. Check throttle switch (grey) it has to return to the park position everytime you let off the gas. Also, have the injectors changed, if he hasn't already ?. Is the engine using any oil?, M103 engines are notorious for bad valve guides and seals, if you have one cylinder burning too much oil you'll get the "hole" upon take off. Now keep in mind, you're not gonna see blue smoke, you will only notice this when you go a 400 mile trip and upon return you notice that the engine is 2 quarts low on oil. 2 other possibilities, Bad computer, or pneumatic fuel pressure regulator is going bad. it's best to swup the computer out from another car to illuminate inproper function.
It's obvious though that when the engine shuts off like when you put it in reverse, or slowing down when you approach a traffic light it's running lean at that moment, which reminds me the problem could also be in the air/fuel metering sensor, which is a oval 2 inch long, 3 wire connector sensor on side of the fuel distribitor housing. Keep us posted. Martin. Autobahn Auto (757) 723-2112
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    Martin, my '89 300e does exactly that. WHERE is the oil going?? if it's not burned and I also don't notice any _excessive_ dripping, just a bit here and there. What exactly needs to be done to fix this problem? thanks for any help.
regards, Guenter
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Guenter, I gues you're german?. Anyway, you need to have the cylinder head pulled and the valve guides and seals replaced. Don't let the dealer or anybody else fool you into just doing the valve seals without pulling the head, this will fix the problem only for a few month's. I'm not sure what the average shop out there charges, I charge $ 1,250, parts and labor, this is what comes with that, valve guides, and seals, clean all the valves, cylinder head gasket, manifold gaskets, new spark plugs (bosch H9DC), oil change with filter, and finally a new valve cover gasket. Also, the upper front timing chain cover will automaticly be resealed, cause often they have a leak there anyway. Martin Autobahn Auto (757) 723-2112
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This isn't something that can't be fixed with a one time adjustment, I get these cases from time to time. Martin. Autobahn Auto
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Have you checked these parts:
throttle microswitch:
http://mercedes.thebenzbin.com/?year 89&make=MB&imageField22222.x3&imageField22222.y=7 Check that the idle responds when clikced on and off
EHA Valve (governor) http://mercedes.thebenzbin.com/?year 89&make=MB&imageField22222.x3&imageField22222.y=7
I do not know how to check this part other than if it is leaking you will smell gas.
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Thanks for all the ideas on this problem however the problem still continues.
To add to the observations I have noticed that the rough idle becomes far more pronounced after the car has reached full operating temperature, in this case a little over 80 degrees. Does this mean anything to anyone?
Air/fuel ratio has been checked and adjusted to spec by mechanic. This helped for a few day but the problem has returned again but it was never totally fixed.
Vacuum holes were were also checked for leaks and came up OK.
Thanks
iain
On 12/6/03 8:08 PM, in article snipped-for-privacy@posting.google.com, "PB Patches"

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Iain, The part in your post regarding changing the injectors "they were very dirty" makes me believe the remainder of the fuel intake system is also "very dirty". Carbon build-up in the intake and on the back of the intake valves can cause a littany of idle, stumble and poor acceleration problems. Run a can of BG 44K through the tank,It's an inexpensive way to eliminate carbon build-up as the source of your troubles. http://www.storesonline.com/site/598452/ is a source and the prices are very competitive, only drawback is they only ship to the 49 states.
Best of Luck, Paul
wrote:

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I was experiencing a similar problem with my M103 based Brabus 3.6. However I was also loosing water and getting oil in the water as the head gasket was gone. My engine has not got hydraulic lifters so they needed adjusting which totally smoothed the engine. I believe your car has hydraulic lifters as I think this was a modification made by Brabus so you shouldn't have to adjust the lifters but if they are hydraulic then maybe they need replacing?
Mehmet Sanliol

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5000! I think you may mean 500 (I hope!).
Check that there are no vacuum leaks anywhere, that the air filter is clean, remove and clean out the idle valve as these can get clogged - I used a fuel injection cleaner on mine which really helped with the idle on my 260E. Replace the plugs, rotor arm and distributor cap as well as these should be done from time to time to allow for the best possible running of the engine. Check also that the CO content at idle is correct.
It's also worth checking that the engine mounts are in good order, they are often worn out and this allows a lot of vibration to be passed into the cabin.
Good luck,
-- Al Bolton, G4VSQ 1990 Mercedes 500SE 128,000 miles http://www.reading-city.net/Vintage_Radios

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