Mercedes-Benz Forum banner

1 - 7 of 7 Posts

·
Registered
1990 420 SEC
Joined
·
7 Posts
Discussion Starter #1
Hi,

My 300E has an idle speed of about 1000 - 1200 rpm when warm.
If I stop the engine and start it again without touching the throttle the idle speed is perfect at about 700 rpm but as soon as I have touched the throttle the idle is stuck at a high level.
After a high idle of several minutes it can sometimes suddenly drop down to 700 and stay there.

I guess air leak is a possible reason but I think it would then always stay high?

Work done so far:
  • New idle Control valve
  • New sparks, leads and distributor cap
  • New injectors
  • New fuel filters
  • New fuel pump.
The car will not pass the yearly inspection with an idle above 900 so starting to get a bit desperate.
Any ideas?

Many Thanks

//Dan
 

·
W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
Joined
·
12,634 Posts
Check the OVP relay Dan and put a few drops of trans fluid on the throttle linkage.

Sent from my XT1710-02 using Tapatalk
 

·
W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
Joined
·
2,260 Posts
Agreed with Jayere, if you have a voltmeter measure the average voltage (DC) on the IACV connector while it is plugged in (insert small wires in the connector).

If it is zero volts during the 1000-1200 rpm episode, it is electrical so go get yourself a new OVP and take note of the date code on the old OVP as a datapoint and post it here. Mine generally last ~10 years on average before they start acting up.

- Cheers!
 

·
Registered
1990 420 SEC
Joined
·
7 Posts
Discussion Starter #4
When i saw that my OVP was the newer version with two fuses i assumed it was Ok but perhaps that's not the case then. I will measure the voltage but firs I will put some trans fluid on the throttle linkage to see if that makes a difference!

Thanks

Dan
 

·
Registered
'95 E300 DIESEL, '91 600SEL, '92 600SEL
Joined
·
16,843 Posts
The OVP is a wear and tear part. Best practice is to replace it at least with every other battery change or 10 years whichever comes first.
 

·
Registered
89 300E; 00 E320
Joined
·
2,510 Posts
I replaced my throttle cable recently since the plastic adjustment screw broke. And it seems to have made a difference in performance.

There was a good idle before and after replacement so I can't really correlate the change with idle improvement exactly, but it even seems to improve shifting between gears; so much so that I also had to adjust the transmission bowden cable a quarter turn or so after replacement.

Maybe the seemingly improved performance is imagined, but I think it is probably due to better mechanism movement after the change and of course the adjustment of the throttle.
It would be nice if I could tell you that changing the throttle cable would fix your problem, but I know it won't hurt it; and my guess is that you will also get better throttle performance and more accurate adjustments of both throttle and transmission shifting.
 

·
Registered
W124
Joined
·
4,692 Posts
No additional advice here; I am just lamenting. Problems like the OPP is having crop up too often with the older cars and its unfortunate that they will keep an otherwise good car from passing inspection and ultimately lead to its demise. Replacing a car that essentially works fine other than a Bosch injection issue is a tough one. Hope you find a simple solution. If not, maybe we can do a group buy from Edelbrock to have them cast an intake manifold that allows a Holley 2bbl to fit on an M103.
 
1 - 7 of 7 Posts
Top