more idle questions -- 108 4.5 - PeachParts Mercedes-Benz Forum

kpb · #1 03-23-2004, 01:42 PM

Have searched here but did not find info directly on-point.

Within the past ten days my 1972 4.5 108 has started as usual but does not proceed immediately to the frenzied fast idle as it did in the past. If I let it sit idling, it eventually does speed up only to reduce again as the water temp comes up to 175F. If I try to drive it immediately before it has gotten to a fast idle, it lurches, gasps and surges quite unhappily. Any clues?

Subject has new plugs and wires. Have not touched the MAP sensor or any other item in the fuel/ignition chain.

Tomguy · #2 03-23-2004, 02:29 PM

Plugs are copper-core (not platinum, not resistor) and gapped at 0.032" right?
You used solid (non-resistor) wire and either the original spark plug boots and distributor cap connectors, or the set came with the proper ones (5K ohm spark plug boot - not the generic all rubber ones but the metal-protected ones, and 1K ohm dizzy connector)

Otherwise, sounds like what I think I've noticed with my MB - too rich when cold! I know it's supposed to be rich but mine is TOO much so, makes it idle VERY rough (like it's only hitting on 4 cyls or so). Runs fine if I push the gas so I know it can't be trigger point or ignition malfunction. I'm gonna back the map off the slightest (not even 1/4 turn) if changing the idle air screw didn't help enough, or if leaning the ECU doesn't.

kpb · #3 03-23-2004, 02:47 PM

and the ECU is the adjustment on the ignition brain? BTW, tomguy, because I read some of your posts BEFORE I got my noew plugs and wires, they are the correct ones

This idle thing only concerns me because for the first three months of ownership it idled F-A-S-T right away and now it seems as if it needs to pre-warm to even fast idle.

Tomguy · #4 03-23-2004, 03:03 PM

Yup, ECU is the "wheel" on the right of the D-Jet brain unit. Right richens, left leans (opposite of MAP)

j9fd3s · #5 03-23-2004, 08:45 PM

i just got a set of "normal" bosch wires to replace the tired/misrouted "normal" bosch wires that are on there. should i have something else?

mike