300E Low idle then high idle surge
 

When I first start it the idle is very low and uneven, then after about a minute or two it will jump to 1000rpm and then quickly settle back to a normal, somewhat smooth idle. This started happening immediately after I changed the water pump. Did I disturb something?

The OVP and O2 sensor have been recently replaced.

1988 M103, 60K miles

Idle control valve. It's under the air cleaner.

Give it a clean with some electro contact cleaner.

If it's not the ICV then it should be OVP. I once had this problem and the new OVP solved.

OVP is good and I cleaned the ICV, still acting weird.

if another clean up does not rectify then may be time for a new ICV.
Do re-clean the OVP and FP relay contact sockets ,pins.
mak

+1 for cleaning contacts....

Is the OVP new or repaired ? Anything other than new I would be wary of.

OVP is new. When I first start it (cold) idle is low. If I unplug the ICV, idle stays low, the same. Idle will kick up to normal ~750 after about 1 minute with ICV plugged in, getting power.

If the idle stays the same when you unplug the ICV when cold, I would think it is sticking closed.

I would have expected some sort of change if you unplug it. If you are getting voltage to it then I would suggest changing it.

Try replacing the water temperature sensor (mine was on manifold towards firewall on top driver's side)....helped my idle with same issue after I replaced OVP and O2 with little improvement. I'm not sure where it is on that car. I have a '91 300E. Only thing I can think of that is related to something the water pump replacment could have an effect on besides ICV.

I will check water temp sensor and power ICV and report back.

Today I replaced all the injectors, idle and engine response is better but still idling very, very low until about 2-3 minutes then something kicks in and it's fine, normal idle. Temp sensor, FI relay or OVP? What do you guys think? Again, this happened the moment I restarted it after replacing the water pump. I must have disturbed something but all looks OK.

I found and old OVP relay and plugged it in. Problem solved. I'm always sceptical whenever someone says it's the OVP no matter what is wrong but in this case it was correct. Thanks.

Glad to hear and good to know but weird that it would happen after you changed the water pump. Are you sure that there were no signs before that? Something had to cause it to short out or become defective during the swap or after. At least now you'll know your OVP is good if something else comes up.

No idea how the OVP went bad when the water pump was replaced.

well since you already replaced the ovp,the iac,i would check the eha,it controls the cold starts it leans and richens the fuel mixture,another tell tale sign that the eha is bad is a smell of gasoline when starting,and ruff idle almost conking out then catching and idling up to about 900-1000