560SEL idle surging
 

Upon surfing forums for a while, I didn't really see anything that had my specific symptoms so I'm asking here.

Most of the forums talk about a high idle or fast idle. I don't have any of that.

When the car is cold, I turn the key and it pops up to about 1100 or 1000 rpm....then within 5 seconds the rpm drops back down to the 650 or 700 or whatever and is normal. So those two things are fine.

However, here is the problem. Like clockwork, about 20 seconds later, I hear some sort of click like a relay or who knows what and it starts surging. It surges up for about 1.5 seconds, then back down for 1.5 seconds. Just up and down, up and down in a rhythm. It's only surging like up and down maybe 500 rpms. On the low side of the surge it sounds like it may sputter like it would die, but catches itself. Other than that the car drives fine.

What's weird is the idle is fine and steady upon first startup. If I let it cool for 15 minutes, and start it again like it's a 'new' day, it does the usual 1000 rpm for like 5 seconds, slowly drops down to 650 or 700 and holds it just fine. Then after 20 seconds again, some sort of "click" and the surging starts. The click almost sounds similar to when your ac compressor kicks in, but of course I have the air off.

Any ideas??

I'm pretty new to these petrol engines but it seems to me that all of these systems consider temperature as part of the engine management system. So I would quickly check all electrical connections to as many of the thermostats you can identify as possible!

I would then also see if you can read any fault codes from the engine management system - these days the car has some way of telling you what is wrong.

Can you tell where the click noise is coming from? I believe I've heard this before but I am not remembering where/causes/etc.

I wonder if it could be emissions related, maybe something with the smog/air pump engaging.

This part is actually normal. For the first 30 seconds or so after you've started the engine CIS-E is in a control mode where it will hold the engine fuel/air mixture in place at 50% duty cycle (if observed at X11 port).

After that 30 seconds or so the electronics take over and start to vary the mixture by reading the myriad of sensors and adjusting the EHA. Duty cycle (viewed at X11) should now start to vary. If it sits at a certain percentage (10,20,30%,etc) and does not vary then the CIS-E unit is indicating a fault.