W126 high idle after air filter change

[Fast_Lane_Dane]

I've changed the air filter on my -82 380SE the other day, from the standard paper type to a K&N filter. The K&N lives up to every word reg. increased air flow - problem is that it - alas - also have lifted the idle revs from 750ish to 1.100, peaking up to 1.400 when I put it in neutral and then quickly back to 1.100.
I am aware of the many, many posts on this forum and others reg w126s and high idle, but haven't seen it as result of a mere air filter change. As anyone who have had this fault knows, there's apparently no idle adjust knob or similar on the M116/M117 engines (dunno for the M110's), it's all controlled by the reputed idle valve and the likewise reputed control box in the passenger footwell.
So: Long story, short question: where do I start, cleaning the valve? Checking the solderings on the control box? - or is there indeed a shortcut to get the revs back to normal when one only have changed the air filter?

Btw., Dooogie has posted a thread

where another member suggests the idle valve should be dismantled, sprayed with carb cleaner and 'shaken in rotary fashion'. It seems a bit destructive, and this last member has status 'Banned'??? Does this mean that I in no way should follow his pretty drastic advice? (apologies if the Banned status means something entirely different)

Regards, Hans, DK

 

[television]

Hej.

There are 3 parts to it, the throtle posstion switch that tells the main ECU that the egine is at idle. the idle relay tells the main computer that the engine is at idle, and tells the idle control valve the proper RPM.

You have knoked something as your engine at idle is running on the main ECU look at the switch on the throttle cable

Hej Då

 

[wireman]

PUT THE PROPER FILTER ON.

I believe in keeping as much filth out of my engines as is possible, you cant get more airflow without bigger holes in the filter and bigger holes mean bigger muck.
Bigger muck = bigger wear and tear.

A petrol engine can only benifit from less inlet restriction at full or almost full throttle and when can we drive our cars on full throttle continuously?

Your engine idle speed is indeed controled by the management system and a fault must have occured on some part of this, the idle valve bypasses the throttle plate and if its sticky could be the culprit, this may cause somewhat variable idle speed, another possibility is an air leak around the idle valve or throttle body, the associated rubber air hoses can have small splits that are difficult to see.

 

[Fast_Lane_Dane]

Hi television and wireman, sorry for the late response. Televison, you write that I should look at a switch on the throttle cable? The throttle mechanism on my w126 is all rods (at least in the engine bay) and there's no switch operated by these?.
Wireman, the K&N filter should be cleaning the air sufficient, I guess they wouldn't give the million-mile guarantee if not(?) One thing I did notice is that the car response quicker to the throttle pedal (i.e. more oomph ;-) The downside is the high idle, which seems to drop from 1.100 to 800+ when the engine is warm, but if I then stop the car and start again immediately after, it's back at 1.100.
I will dismantle the idle valve and see if any muck or like is sitting in/partially blocking one of the vaccum hoses.
Another thing which came in mind is that the control box might have a memory function which can be resetted by disconnecting the battery - might be chasing a red heering here, but can anyone give a definite yes or no on this one?
I'll return after I have given the vacuum hoses a go.

Cheers, Hans

 

[GEORGEROV]

Hi Hans, If you are altering the air induction side you should check the emissions with a co meter and adjust the mixture to give the desired 1% reading. This will probably bring the idle speed back to normal if the other components are in good shape.