I have just bought a 190 Mercedes 2.0E 1989 last week.
The car has very good shape, full original painting, no rust at all.
Everything is working, the engine runs smooth, pulls OK, no smoke, great idle, but a little bit high I think (about 950).

My problem is that I got pretty low mpg, and I know it should be way better.
Just consumed my first tank of gas, it made only 306 km by using 50 liters of gas, which makes about 14 MPG or 16.5 l/100km.
AFAIK it should consume somewhat between 20-30 mpg depending on driving style/road conditions, etc.

I don't know if it's related to consumption in any way, but the engine starts perfectly when the engine is cold,
but drops RPM for couple of seconds when started warm. (Without pushing the acceleration pedal.)
After a few seconds, it flattens nicely (at about 950 rpm).

I have replaced the air filter and the plugs today, so I may tell after a few days if that changed anything.
There's no smell of unburnt petrol from the exhaust, and the all of the old plugs looked quite nice red/brown, no black deposits, oil, etc.
Do you guys any idea where I should start fixing this?

Any help is highly appreciated!

Thanks in advance,
moire76

check to see if brakes are dragging.Feel wheel and see if hot after driving.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Hi Oldsinner!
Thanks a lot for such a quick answer, highly appreciated!

"Unfortunately" my brakes are OK, bought the car with new discs at front, and rear two are also ok, the wheels can be spinned by hand easily.

My o2 sensor is suspicious for me, especially because of the rpm-drop at warm start...

moire76, recommend replacing the distributor cap, distributor rotor and ignition wires with Bosch parts unless you know they have been replaced within the last 30,000 miles. Hopefully you used the spark plugs specified in the Owner's Manual with the gap set properly. Make sure the tires are inflated properly ... even a few psi over the values shown on the fuel filler flap. If those things don't improve the gas mileage then there's a chance the cylinder compression values are low, resulting in low gas mileage. There's always a reason folks are selling a vehicle that appears flawless.

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Fred Hoelzle

Hi Ferdman!
Haha, you're absolutely right, there's always a reason for selling any car!
Let's hope first that there's nothing serious! I will have the chance to worry about things when they become reality.

Thanks a lot for the tips too!
The distributor cap seems to be brand new, but I will check the rotor inside to make sure.
I doubt it would be Bosch, but we'll see it later. The ignition coils seems to be very old, they might be the original ones from 1989, they deserve replacement for sure.

I bought Bosch plugs and they were all set to 0.8 mm, which I think is OK. I checked the gap and installed them myself, today morning. All tires are inflated to 2.2.

updates: the rpm-drop at warm enigne start getting worse. Today I stopped by a mall in a deep garage, and I just cant start the car after 20 minutes shopping.
When starting, the usual rpm drop came, but this time, it did not flatten, but stalled. After that, just cranking and nothing happens. I smelled a little gas from the exhaust, but just slightly. Cranked and cranked quickly, but did not catch it. First I thought that its getting rich, and the new plugs may be flood, but I did not have tools, so I got a taxi to home for the tools, and got back and took them out. They were dry. I put the old ones back in. NOthing.
Ok call a friend for suggestion, check if fuel pump is starting up with ignition, yes, it did, then check if its sparks, oops, it was shocky, so yes, it sparks.
So now what the heck?
Needed to leave the car for a minute, and when I came back and just tried it with full gas, and for the second time, the engine started. I already tried the pedal-to-the-metal starting the engine, but did not work. What is changed? I locked and unlocked the car with the remote.
I have a third party remote alarm, but I wouldn't think that it would have any immobilizer function, but to be honest, I do not know anything about my alarm&remote lock, it just does its job, locks and unlocks, and turns the alarm on and off.

After that, I stopped and started the engine several times, and it always started immediately, as always, since I bought it last week.

Misterious...

moire76, I would be wary of any electrical add-on to your automobile. No telling if the person who installed it was competent, or perhaps inadvertently damaged some wiring during the installation.

You mention ignition coils. As far as I know there is only one coil for that engine.

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Fred Hoelzle

Hi Ferdman!
Yes, you're right, unknown fitting of any aftermarket device may easily be a source of problems. Thus I have tried to start the car while locked it with the remote alarm from inside, but it just triggered the alarm, but did not prevent starting the car. I could also turn it off while the engine was already running, so it seems that its really just an alarm
and nothing more.
Sorry, of course there is one coil, I ment the ignition cables that are between the ignition distibutor and the spark plugs.

drop off in mpg is almost always a failing o2 sensor.

i would take care of that issue first.... stall at warm start...and then no start could be a failing crank position sensor

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1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


[/SIGPIC]

Thanks, Lee,
I also suspect that my o2 sensor could be failing.
First I want to use a half tank of gas to see whether the new plugs and airfilter change brings any improvements in fuel consumption, then I will try replacing the o2 sensor.

Wouldn't a failing crankshaft-position sensor cause hectic/rough idle too?

when i lost a cps.... the car would start perfectly when cold.. then after driving it a bit...it was just stall.... dead stall. at first i could restart it.. but in a matter of a couple of weeks... it would dead stall... and i had to wait for the car to cool down a bit... once it took 30 minutes to cool down.. i replaced the cps and never had a problem.... no idle issues when running... there is also a camshaft position sensor which doesn't ever seem to go bad... crankshaft sensor will take you 45 minutes to replace the first time....

this was on our 89 ce... with a 103 engine....

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1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


[/SIGPIC]

wow, how did you find out that it is the cps??
I would never think of it before replacing every single fuel supply component one by one...

Yesterday, I have found a thread about spark plug lubrication. Based on the conversation there, I'm thinking that I may caused the starting problem.
To prevent stuck, I applied a little copper paste on the plug threads that might cause inappropriate ground for the plugs.
Afaik copper paste is conductor, so this is just another theory.
I drive about 50km in city yesterday, with a few cold and hot start, and no problem at all with the startup.
I'm also curious about the consumption with the new plugs, 60km from last tank fill, and the gauge is still at full. I know it's not a linear scale, though. My Mondeo had full gas gauge after 120km with a low fuel warning at about 480km...

moire76, I always apply a light coating of Never Seize to spark plug threads before installing them and have never experienced any ignition problems ... same for Oxygen sensor threads.

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Fred Hoelzle

Thanks, Ferdman, that sound promising to me, as usually I also use a little lubricant for most threads and never had issues!

I'm now at 80km since full tank, the gauge arm started descending...