I thought I would post this about my 88 300SE. The car seems to be having some strange issues with power, starting and idling. It takes two tries to get it to start and idle without stalling. It idles at about 650rpm with only minor fluctuations. The shifting is nice and smooth but it seems to be a little slow or late shifting. Occasionally when decellerating and coming to a complete stop, it will stall but will start up without any problems once at a stand still. It just doesn't seem to have any power and seems to be the slowest moving six cylinder that I have ever driven. Any suggestions would be appreciated as always.

Things that I have had done to this car:
Complete Valve Job ; replaced head gasket and all other gaskets, hoses and seals on this car including intake manifold gasket and injector seals.
New Timing chain, Tensioner and Guide Rails
It came with a new Exhaust system.
New Idle Control Valve
New Distributor Cap and Rotor
New Spark Plugs and wires immediately after valve job.

I had this same problem before all this work was done. It runs alot better but still just doesn't seem to be performing like it should.

I think David Poole would say it could be the fuel distributor as in my case.

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1996 E320 since 1/16/08, 171K miles as of Feb 2011

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1989 300CE - R.I.P. Dec 29 2007
Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE

If it stalls when warm, you might consider the infamous OVP - over voltage protection relay - costs about $50. How about the air filter? Has it been changed?

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

Could be many possibilities:
1. The OVP itself is not likely to be bad BUT its contacts could have been widened. Remove and check, narrow the contacts.
2. Coolant temperature sensor (fuel injection temperature sensor) either is bad or its signals are not reaching the computer due to a broken wire somewhere. Check the connector on the sensor. A disconnection could put the car in a limp mode.
3. Check the EHA, this is normally providing enrichment during acceleration.
4. The air meter sensor, on my 87 260E there is a pot, I am not sure what you have on your car, could be the MAS, this can cause hesitation in the engine because the air intake is not correctly known to the computer
5. Check crank shaft position sensor, this can cause intermittent shutdowns. (less likely in your case)
6. Speed signal may not be availabe to the computer
7. Check vaccum, need to have about 20 on the vaccum gauge at idle, otherwise could be the catalytic converter

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Saumil S. Patel

Well I did also replace the air filter and the coolant temperature sensor (since I broke it). It does stall when warm like you say so I will look into that relay. Is that the same as the overload relay, the one with the 10A fuses?

Is there a way that I can reset the computer on this car just incase it was in limp mode which would seem to make sense where the throttle response and shifting is concerned.

I am not sure about resetting the computer, I thought it will check the temperature sensor at startup and then will auto reset.

If this car is similar to my 87 260E then the last sensor (closest to the windshield) on the engine block is the fuel injection temperature sensor. Disconnect the cable and check resistance across the sensor terminals. When cold (20 deg C), the resistance should be between 2.5 and 3.5 Kohms. At the engine temperature of 80 deg-c, the resistance should drop to about 250 to 350 ohms. For the system to go into limp mode, I would think that either the sensor has very high resistance OR the cable from the sensor to the computer is broken somewhere.

Another less accurate test would be to see what happens to the RPM when you disconnect the sensor cable when the car is at 80 deg-c. The RPMs should drop a little, if nothing happens, the sensor signal is not reaching the computer.

Infact, I am wondering is you just attach say a 500 ohm resistance across the sensor cables, the car would have some air/fuel mixture problem when cold BUT it should never get into a limp mode. This only works if the sensor wire have no breaks and the signals reach the computer.

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Saumil S. Patel

Disconnect the battery this will clear the computer!

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William
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1987 420 SEL - Like a fine wine only better with age

This car has no "limp home mode"! The problem you describe sounds like a clogged catalyst. Loosen the bolts where the cat connects to the manifolds push the pipes back a little and test drive it, If the power is restored you need cats.
Catalysts overheat and partially melt on engines that are burning lots of oil. Was high oil consumption one of the reasons for the valve job?
Good luck Mike

Stall on decel when warm as described above is quite often the result of a tired OVP, especially on this yr/model.

Trying to clean or otherwise repair an OVP is an exercise in futility. You replace them.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

I took a closer look at the OVP today and found that not only was it pushed deeply into the compartment with the bracket removed but the protective cover for the 10A fuses was gone. When I took it apart I found alot of corrosion so I will be replacing the unit tomorrow. Hopefully that will solve the stalling problem. As for the slow starting, I adjusted the Mass Airflow Sensor Plate which solved the problem. It now starts right up but there is still a slight fluctuation in idle. I will look into the catalyst as well since the valve job was indeed performed to repair leaky old valve seals. Thank you all for your input, I will keep you informed...

Two things you have not mentioned that I've had to replace on my 88 TE:

Injector holder o-ring seals (bet you didn't know there was such a thing, eh?)

Boot between air flow sensor horn and throttle body. This shrinks and leaks at the idle control valve hose fitting (the fitting will pull out easily if bad) and at the clamp connection to the throttle body. Big air leak, crappy throttle response, hard starts, and stalls on decleration (plus dirt in the ICV, causing it to stick). Check the clamp on the throttle body -- if it's loose or has been completely tightened (ends touch) the boot is shot, time for a new one.

Check the idle control valve hoses, I've had one split in a couple years of use along the "seam" -- too much mold release agent, I think, didn't vulcanize together.

Check the line to the brake booster, and the booster itself, too -- a split booster diaphram will cause stalls on braking.

And check the cap and rotor for carbon tracks.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I did replace the injector holders and seals, the originals were rock hard and shrunken from the last 20 years of use. The throttle tube is just fine, seals tight, all the other tubing has been replaced as well, cap and rotor are new. I took it out for a test drive today with the new OVP and had no stalling issues, it started right up and idled like a new car with the recent adjustments. I do think the shifting is a bit off, that is probably why it seems to be lacking in performance. It would seem that it shifts really slowly and possibly a little late or it could seem late based on the duration of the actual shifts. Any ideas on what this problem could be?

I just found that the transmission is leaking fluid now. It appears to be leaking from where teh kickdown switch connects to the transmission on the passenger side.