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2003 S320CDI 133K miles
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29 Posts
Discussion Starter #1
Hi guys, not been on here for years since I had my 1990 500SEC. Have since had a 1992 S500 but that was a while ago.

have just bought a new Benz. It's a 1988 300SE. It is a 1 owner car from new, new MOT and full main dealer history........and has only done 67,000 miles!

Couple of faults:

1) heat only controllable from passenger side vents. I've looked on the forum and pretty sure its the duo valve. Heat does occassionally come from drivers side, but you cant control it and its cold most of the time, unless sitting idling.

2) Slight rattle from engine at start up, only lasts for a second till oil pressure gauge goes to max. Also only happens first thing after it's been really cold.

3) Oil leak from timing seal area.....will get round to this. Can the oil filter be changed without draining the oil???? It is the screw down metal can type at the top rear of engine behind the air filter.

3) Clunk/jolt going from P/N into D/R once the engine is hot. Goes in smoothly when it's cold. Once in D gearchanges mostly smooth, with the occassional jolt.

4) I dont think the mixture is right. This is my big annoyance just now and the one I really want to resolve. The car idles smoothly when cold. With the car at operating temp, and in P, the idle speed it around 700, the oil pressure moves about a little but is mostly at 1.25 bar. There is an intermittent rough idle when hot, will sit smoothly for 30secs then have a wee cough, then be fine, then do it again. Sometimes it will do it at shorter intervals than 30 secs sometimes longer. Oil gaige moves about in conjunction to this cough. It ONLY noticeably does this when hot. From cold to normal temp, it is pretty well smooth. If it has been on a long run eg 100 miles without stopping, then is left to idle, the idle is very rough. Last time I thought it was going to stall. Next morning, it was smooth again when cold and intermittently rough when hot, same as usual.

Not sure if this is related, but it also feels underpowered. When at 40mph, if I press the gas pedal lightly the economy gauge goes right down but not much happens, unless you give it a good push of the pedal. Under hard acceleration the car pulls smoothly. If you accelerate normally the car pulls smoothly for a bit, then at about 60mph will start to feel like it is dragging something for a second. It's like the feeling you get when you are on the motorway and a lorry pulls past you making the car slow momenteraily, or when the wind blows agianst you in a gust when driving making you slow for a second. Thats the best description I can give of it, its a very smooth drop in speed, and only lasts half a second or so. It also does this if you accelerate up to 60mph then slightly take your foot off the pedal. After each momentary drop in speed, it has a momentary surge of power like it wants to go. It does all this very smoothly there is no jolt ect and I thought it was just wind for a while. Again, it ONLY does this when hot. Makes me think the mixture is not right?

car has only done a few thousand miles in teh last 10 years and I'm not sre Mercedes properly serviced it, even though the owner paid them as the plugs and fuel filter looked old, and the dizzy cap contacts are quite worn. Yet the air filter is brand new as is the antifreeze and oils. The original owner was disabled, so I'm thinking the dealership took advantage of him.

I have changed all the plugs to Bosch Super 4, replaced all the plug leads, replaced the fuel filter. Took idle valve off and looks clean and closes when ignition turned on. The distributor contacts are quite worn, but given that the idle and power is fine when cold, I assume that the worn contacts would cause a problem under all temp conditions and not just when hot? I plan on changing the cap and rotor arm this weekend though.

Any suggestions would be appreciated!

Alastair.
 

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SuperModerator
1986/1990 W126
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14,132 Posts
Good move with dist cap and rotor. Bit expensive but if youre lucky that will be it. Apparently the sixes use them quite quickly.
 

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Registered
2003 S320CDI 133K miles
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29 Posts
Discussion Starter #3
Sorted the idle and surging when driving issues :)

Took the air filter off and found a hex head screw that was sping loaded. Also found the throttle stop screw. Have backed off the throttle linkage so it's sitting right on the stop, then backed off the spring loaded hex screw all the way. car would not fire with the hex screw backed off so I gradually turned it up till i got the car to fire. It ran very very rough, but after minute turns of this hex screw, I got it running very smoothly. Lots more power now and the idle is pretty perfect, given its a 22year old car! Still to change dizzy cap and rotor arm.

Next questions.....can I change the filter without draining teh oil first. its a metal can type filter at the top rear of the engine next to the air filter.

The heated rear screen button when pushed lights for 10 secs or so then starts flashing, not sure if it's actually demisting though, is this normal?

Plugs seems a bit sticky, they are brand new and have gunked up a bit. looks like burned oil on them. The car has FMBSH and only 67,000 miles. But has only done a thousand miles or so in the last 10 years. Could the valve seals have failed from sitting. All 6 plugs are identical to each other, would all the seals fail at the same time?
 
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