StarGazer

have a 190e 2.6 and it idles funny...

1) when u start from cold (say overnight - 5~6 hrs ie. when engine temp is below 40 degree - as hown by temp gauge on console) - the car start fine but tends to idle high ... it will be around neary 1500 when in park ... the moment is move it to R or D it will idle down to just short of 1000 . The oil pressure is at 3 - full - which is what it should do....

2) drive around for some time - engine temp is around 80`85 Deg C - the car idle automatically come to normal - in D or R it is around 600 and in P it is 750 - which is should be.. however the oild pressure when in R and D ( e.g sitting at stop light) pressure is 0 (zero) - the moment you hit the gas the oil pressure come back to normal..
Also the oil pressure varies with engine temp - e.g say at 70 the oil pressure with drive ear enaged is between 1 and 2 or higher..

I think this is more on the Idling side problem rather than the oil pressure side...

I guess there could be problems from the oil pressure side - faulty oil pressure sending unit - which is beside the oil filter ...

I would appreciate nay better suggestion where to start..
Thanks in advance

mctwin2kman

First Mercedes specifies that Oil Pressure at engine temp (80+) is supposed to be .2 Bar so your gauge could be a hair off or the fact that .2 Bar is low in the scale. Second 1500 RPM is roughly the Idle for warmup. Idle settles down somewhat after 30-60 seconds as the engine starts to warm. Third when Oil Pressure is low at idle do you hear any ticking from lifters? Also when was the last time you changed the oil? What Oil did you put in as well?

StarGazer

Thanks for your inputs -- I am not sure what you mean by the tciking sound of the lifters ... if u sould be more specific where I should to look for that sound - i can revert back to you...

Also I have 10W 40 Castrol and the oil change has been around 2.5 K back...

I underdstand idle has to remian high for warm up but not be the same once car temp reach 40~50 -
Just today I drove to work - car started with idle 1000 - pressure 3 bar -- perfectly normal -
when I reached work after 5 mins of driving and 2 miles - and I put the car in park (P) - idle jumped up to 1500 - engine temp showed 60 Degree..
so what i did was just race the engine to 2300~2500 rpm - and let of the gas - i did not hold the gas at 2500 - just make the engine reach it and let off... and the RPM fell back to normal 750 ..and idle normal/perfect

I have also noticed that when engine temp is 85~90 - the oil pressure in D is just above 500 rpm..

So basically some how idle falls wih temp but i guess it should be stable once at 750 rpm - no matter how high the temp - and i guess Idle automatically ajust the oil pressure and hence the low pressure..

mctwin2kman

You should not hear the hydrolic lifters ticking at all. If there is really low oil pressure and not enough oil is getting to the lifters then you will get a ticking sound from the top end of the engine, under the valve cover.

As for the idle issues, it sounds like you have a sticky IACV or a vacuum leak or AFM rubber boot cracking leak.

StarGazer

I donot hear and funny noise or ticking as far I can say ... but will surely check ...
Also I guess I can open and clean the IACV(idle air control valve) but
what is a "AFM rubber boot cracking leak" - pls eloborate ...
thanks

mctwin2kman

There is a boot between the Air Flow Meter and the actual Throttle Body. They crack and allow air to bypass the AFM and thus cause an air leak. This is seen more when cold. Also the rubber hoses that connect the IACV to the rest of the intake system when old get hard and start to crack and leak. This will also cause funny idling issues.

StarGazer

Thanks again .. when u say the rubber boot to the AFM do u mean this:
http://autohausaz.com/secure/PartImages/1031410090.jpg

mctwin2kman

That is it. They crack when they get old! Lots of heat up and cool down. If you have a mirror, dental type, and a flashlight you should be able to check it out for cracks. Or if you have smaller hands you can feel around it.

StarGazer

thanks ... mctwin2kman - today it is raining so will have wait for a clear day to check on the parts you mentioned ..
I will keep u posted as things develop.

marco402

you might consider using a spray on the AFM boot to check for cracks...example: with the car COLD, remove air box, start car, let idle for a minute or two & then 'blip' the throttle to reduce rpms... spray carb cleaner all around the boot and watch for idle speed changes (DONT DO THIS ON A HOT MOTOR or use a water mister instead). While the throttle linkages are exposed it would be a great time to clean, and lube all the pivot points and cable ends too, high temp. grease or even WD40/LPS1 or 2 are ok.. and like previously suggested, look at all vaccum line and hoses, especially those 3mm hard plastic lines that love to crack when handled, the ones that are age-discolored yellow (used to be white). I have never had an oil press reading below .5, even at 550rpm, indrive, 95+F OAT, 90C water temp....usually idles at 1 bar, so maybe an oil change and a increase in viscosity is warrented, but if no valve noise, and normal readings above idle, full oil level, ect... it might just be an indication error as you suspect... keep us informed

StarGazer

Thanks Marco -- I will surely look into it -- I just need time and work has kept me busy and cold from getting my hand dirty..
but will keep u guys updated..

I also found a vaccum diagram - hope it will help other in cases of problems for other ..