'88 300 SE idle and starting issues

[White Knight]

Hello everybody. I just joined and I would be so grateful if I could find some anwsers for some problems I have been having with my 88 300SE W126.

My car is idling around 600rpm and oil pressure is at 1. I have new spark plugs with correct gap .032, oil filter and air filter. When driving oil pressure is at 3 and everything seems fine. Idle also differs between Park and Drive gears. Sometimes after driving I will put it in Park and rpm's go up to 1000-1500 and then put it into drive and back to 600rpm.

Starting the car is odd too because the first start of the day I barely have to turn the key before it turns over and idles nice and smooth. But if I drive some where and stop and then get back in to go it will try to fire up right away, rpm's go up to 1000 and then fall like a rock. In this case I have to rev it up for a minute before the rpm's will hold.

My temperature gauge is funny also because the needle likes to jerk around and then pin its self to the red zone. I know it is not really overheating because it has been doing this for awhile now and thermostat has been replaced. Mechanic says dash needs to be pulled but I feel there must be something wrong in the engine bay.

Any suggestions would be so hopeful and if you need more detail let me know and I will try to supply them.

Thank You,

Peter

 

[Brian WH]

Hi Peter

Certainly sounds like you have an idle problem. The revs in park will be slightly higher, but only slightly not 400+ revs. In drive the engine is under a small load and this reduces the revs. This could account for the poor starting when hot, and in fact the engine could be overheating slightly. The reason for the high revs could be numerous, from carburettor settings to vacuum problems.
What carburettor have you, does it have a dashpot on it, if so it could need a spot of oil adding.

Oil pressure at idle is low, I would have expected at least 2. You have changed the filter but have you changed the oil? Are you using the correct grade?

Finally did the mechanic comment on your problems or not?

 

[White Knight]

Brian thanks for the response. I did change the oil and I am using 10W-30 in 35-40 degrees C. As far as the carburettor goes I thought I had fuel injection but I guess not. It is the stock carburettor that is all I know. Under the air filter is circular piece of metal that goes up and down I believe to the throttle body if that helps. Mechanic said something about an idle regulator but of course it would cost a lot of money just for him to look at for real. Every thing seem to be fine last week. Except for the thermostate gauge that is. Any suggestions on keeping the engine cooler. I know the fan clutch and radiator and thermostate along with other hoses have been replaced within the past couple of years. I have all service records for this car back to 1992. It has never been owned outside of family and friends and finally it is my turn and I want to make things right for it.

 

[Brian WH]

Peter

I was generalising when I spoke about the carburettor, I don't know your particular engine. If it does have fuel injection then that ties up with the mechanics comments. It certainly sounds like a fuel management problem. Sort that out and the high temp and starting problems when hot should be resolved. It could be something simple.

If it is due a service then that is the best time to ask them to look at it.