M103 R&R, now low idle?
 

I just finished a little project on my 1993 190E 2.6 where I replaced the head gasket, cleaned out the intake components, replaced the timing chain rails.

The car started up on the first attempt of firing it up this afternoon and runs great under throttle, but I am having severe issues at idle.

at idle, the RPM drops to around 500 rpm when I coast to a stop and put the car in neutral. at this point, the vacuum is very low and the oil pressure is very low.

I will investigate tomorrow by checking compression, OVP, and IACV, but i just find it strange since my motor was idling just fine before the job.

any ideas? any specific tests i should run?

When the engine is running put your hand on the Idle Control Valve. Do you feel it pulsating?

have not tested this yet.

but I did some more testing today.

Throttle Valve Switch works as defined in the manual

pin 1 = idle contact
pin 2 = ground
pin 3 = full load contact.

pin 1 and 2 are shorted when idling, moving throttle linkages away from idle opens the circuit.

pin 2 and 3 are shorted at full load only, moving throttle away from full load opens the circuit.

IACV still operates when 12V is applied across the terminals. next is to check the OVP relay and try replacing with spares that are laying around.

Compression tests read good,

1: 175 psi
2: 180 psi
3: 180 psi
4: 180 psi
5: 180 psi
6: 175 psi

Tested at normal op temperature with allowed 10 compression strokes per cylinder and all spark plugs removed.

any one else have any inputs?

One more thing to check is the Micro-Switch at the throttle linkage assembly. Make sure it's closed at the idle position.

yes the microswitch is working properly.

I narrowed my problem down to either the IACV or the OVP relay. I swapped both units from my working M103 W124 and my problems magically went away. I am putting the original OVP back in place to see if problem reoccurs.

edit:

original OVP, car still runs fine. it is the IACV. the 300E is now idling funny.