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If I don't start my W222 2015 s600 for a while, the engine might occasionally stall, and usually the ecu will apply a bunch of throttle (3000 rpm) right away.
But aafter that first second, it all levels off and drives perfectly. Tons of power. No codes.
Any ideas? First thought would be fuel pump but it's only on immediate cold start.
If I don't start my W222 2015 s600 for a while, the engine might occasionally stall, and usually the ecu will apply a bunch of throttle (3000 rpm) right away.
But aafter that first second, it all levels off and drives perfectly. Tons of power. No codes.
Any ideas? First thought would be fuel pump but it's only on immediate cold start.
Originally Posted by VII
I'm going to go with throttle body issue.
Originally Posted by silvertonesx24
How could I diagnose?
Originally Posted by VII
Inspect parts for play/fouling, check values with diagnostics on startup.
While not discarding, it would not be typical as:
1. Problem is indicated on full cold start
2. Propensity to stall is indicated (the V12 is not stalling for 1 cylinder)
If I don't start my W222 2015 s600 for a while, the engine might occasionally stall, and usually the ecu will apply a bunch of throttle (3000 rpm) right away.
But aafter that first second, it all levels off and drives perfectly. Tons of power. No codes.
Any ideas? First thought would be fuel pump but it's only on immediate cold start.
Classic symptom. Sounds like carbon buildup on the intake valves. Very common on these engines. The ECU overcompensates for the rough idle on that first start. A good walnut blasting should sort it right out.
While not discarding, it would not be typical as:
1. Problem is indicated on full cold start
2. Propensity to stall is indicated (the V12 is not stalling for 1 cylinder)
If I don't start my W222 2015 s600 for a while, the engine might occasionally stall, and usually the ecu will apply a bunch of throttle (3000 rpm) right away.
But aafter that first second, it all levels off and drives perfectly. Tons of power. No codes.
Any ideas? First thought would be fuel pump but it's only on immediate cold start.
Mine does this if I have not started it in 2-odd-weeks--the cold start cough and rev to 2500 RPM. But it has never stalled.
I think this has to do with battery condition::
a) cold start on slightly low battery, engine comes to life
b) as alternator puts load on engine (to charge battery) RMP drops
c) ECU sees RPM drop, and adds throttle
d) added throttle takes care of stumble
e) ECU sees RPMs rise and takes enough throttle out
f) to allow engine to cold idle where ECU wants it
g) still carrying the added load of the alternator charging battery.
Stone cold; power it up without starting. Observe what the computer sees from sensors. Coolant temperature and intake air temperature must read ambient. Watch engine speed as it cranks and shortly after starting. The V-12 powered 221 car used a crankshaft position sensor that looked the same as is fitted to the E-55 that famously makes for cold starting to dies issues. I don’t know if the same sensor is in our 222 cars but worth checking. My 221 S-65 intermittently did a rough start up after having been parked in warm weather. Winter gas would boil in fuel rails so vapor in the rail. The fuel pump would pump to a pressure (and reportedly quantity) of fuel. Took extended crank time to start up with many misfires, stalls for 30 seconds. Once cleared up ran perfectly. Rarely made for a multiple random misfire code. My 222 S65 has never done this. The V-12 powered cars seem to be challenged with figuring out which cylinder(s) misfire. No doubt due to cylinders firing every 60 degrees which makes picking out a small drop in engine speed difficult.
All V-12 powered cars use port injection. Port injection... zero carbon in intake ports as it is forever rinsed. Injectors are not troublesome as in direct injected cars.
Load from the alternator is immaterial. Engine management applies throttle as needed.
A vacuum leak will make for erratic operation. Certainly worth looking for.
Last edited by JohnLane; Sep 10, 2025 at 12:52 PM.
OP I have seen one 221 S-65 with a dead injector. As it was having an issue it made for a strange misfire. Owner replaced plugs, coil packs and VT with Clark’s goodies. Still did it. Then it let loose and went from (I’m assuming) being a flaky injector to one that was stuck wide open. Engine hydro-locked with fuel. It got a dozen injectors, fuel removed from cylinders, a starter as it cooked itself trying to crank it. Extra gallon of gas was in engine oil.
Client got very very lucky. No bent rods. No other damage.
Fresh set of injectors starter, fresh oil (twice) and she runs like new.
Do real testing to verify that injectors are OK. Read spark plugs. They will let you know if a cylinder is getting fuel dumped on it. Though the above mentioned S-65 had plugs that looked normal. They were almost new after all. OHM test all injectors. Pull the fuel rail with all injectors in it and manually operate each injector to compare spray patterns.
OP I have seen one 221 S-65 with a dead injector. As it was having an issue it made for a strange misfire. Owner replaced plugs, coil packs and VT with Clark’s goodies. Still did it. Then it let loose and went from (I’m assuming) being a flaky injector to one that was stuck wide open. Engine hydro-locked with fuel. It got a dozen injectors, fuel removed from cylinders, a starter as it cooked itself trying to crank it. Extra gallon of gas was in engine oil.
Client got very very lucky. No bent rods. No other damage.
Fresh set of injectors starter, fresh oil (twice) and she runs like new.
Do real testing to verify that injectors are OK. Read spark plugs. They will let you know if a cylinder is getting fuel dumped on it. Though the above mentioned S-65 had plugs that looked normal. They were almost new after all. OHM test all injectors. Pull the fuel rail with all injectors in it and manually operate each injector to compare spray patterns.
I agree that I am starting to suspect the injectors, however once fuel pressure reaches 6.7 bar, the engine runs completely normally. I never have a misfire, plenty of power, etc. No engine codes at all.
Possibly I have a leaking injector, but how to tell which one? I'd prefer not to pull/replace all 12 of them because it's probably just one failing, if it is leaking
I agree that I am starting to suspect the injectors, however once fuel pressure reaches 6.7 bar, the engine runs completely normally. I never have a misfire, plenty of power, etc. No engine codes at all.
Possibly I have a leaking injector, but how to tell which one? I'd prefer not to pull/replace all 12 of them because it's probably just one failing, if it is leaking
I’m not sure if xentry or other scan tool can do this on w222, but you could pressurize fuel system by activating fuel pump. Then with scan tool, individually activate each fuel injector and look at fuel pressure drop when doing so. You’ll see a difference in pressure drop between good ones and leaky one.
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