Hello all, was wondering if someone can give me some help diagnosing cold start system on my 89 560SEC. I have replaced the OVP relay Because it was original black and grey one. With key on engine off I have power at idle valve but no power to cold start injector.. should cold start have power with key on engine off or only while cranking? I’ve read about some thermo time valve and some other type of coolant sensor.. would a bad coolant sensor cause high idle when cold? Can I rule out the temp sensors by shorting wiring connector with paper clip one at a time and see if it makes a difference? If anyone can give me a direction to go that would be awesome 😎

Does "high", as in high idle (speed?) have a number associated with it?
Does the idle speed change with engine temperature?

Hi there, yes idle is about 1500-2000 Rpms cold and gradually goes down after warm up to about 1000 rpms

Check the fuse(s) in the OVP relay; those idle speeds are consistent with damaged fuse(s). As a further check, re-install the original OVP relay with a new fuse.

The fuse don’t seem to have a break in it. I will swap fuse tomorrow and report back with results

Clean the Idle Control Valve and see what happens and if you replace the fuses with new ones use the copper fuses.

__________________
1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

replace the ovp with a new on from mb. once they get about 8 years old, they act weird. i've fixed alot of idle and other issues related to the ovp with a new one.

Hi there, I swapped it with new OEM one and same problem.. Also put old OVP back with new fuse and problem persists

'71:

Although the OVP is the most usual culprit, the sequence that you have gone through pretty much eliminates that cause.
The resistance of the air valve windings should be between 3.5 & 4.5 ohms.
Try unplugging and cleaning all of the connections at the air valve, and at the idle speed controller. The controller is located in the RF footwell. Remove carpet, and a lift-out panel will be seen that serves as the foot rest. The controller is the box at the top center of the covered space.

Thank you for those tips, I will give them a shot in the a.m. .

Would you happen to know which pins at the OVP relay connector should have power with key on ?

Pin/socket #1 (circuit 30) is always hot; direct from battery.
Pin/socket #6 (circuit 15) is switched; key on.