W124 M111 erratic idle and diagnostic trouble codes
Posted: Thu Nov 13, 2025 2:20 pm
I have recently returned from a holiday during which the E220 I have owned for a few weeks operated well for approximately 700 kilometres, except for an issue with harsh and inconsistent idling.
I purchased the vehicle despite its known engine harness difficulties; nonetheless, it appears to have been well cared for and maintained elsewhere. The MAF sensor was disconnected, with the cable coiled behind the engine. It had lost all, and I emphasise all, of its insulation. The throttle body wiring had deteriorated into a conglomeration of green dust. The engine functioned effectively; however, the gearbox performed poorly due to the malfunctioning throttle position sensor. The harness and throttle body were sent to Si-Lec for refurbishment, resulting in significant improvements, except for the idle issue. I examined the codes, which indicated issues with the MAF and air intake temperature sensors (4 and 13). I examined the intake temperature sensor out of curiosity, and it exhibited an open circuit; however, I did not assess the mass airflow sensor. The replacements arrived a few hours prior to the holiday, so I installed them, cleared the codes, and we departed!
Regrettably, it has had no impact on the indolent. The engine initially operates normally at both hot and cold temperatures; nevertheless, it occasionally revs to 2000 RPM after running for one minute while cold. It occasionally has a slight surge while stationary, which is somewhat unsettling in an automatic vehicle. Occasionally, it may stall when shifted into drive; however, once it is no longer idling, it operates smoothly and possesses ample power. It underwent servicing a few months prior to my acquisition, and I observe that it has new spark plugs and ignition leads. I replaced the coils after one terminal detached during harness removal, and I have added a bottle of injector cleaning to the system.
Preliminary study conducted during my absence indicated that the fuel pressure regulator may be the source of the problem. I have placed an order, but I am now uncertain. I re-examined the codes, and the initial MAF and temperature sensor codes had reappeared, accompanied by code 8 - 'Altitude pressure signal from ignition control module is irrational.' I observe that the SRS light intermittently flashes when temperatures are low.
Additional research indicates that the OVP relay may be responsible for the idle issues; however, could this also be the source of the error codes? Any assistance would be much appreciated!
I purchased the vehicle despite its known engine harness difficulties; nonetheless, it appears to have been well cared for and maintained elsewhere. The MAF sensor was disconnected, with the cable coiled behind the engine. It had lost all, and I emphasise all, of its insulation. The throttle body wiring had deteriorated into a conglomeration of green dust. The engine functioned effectively; however, the gearbox performed poorly due to the malfunctioning throttle position sensor. The harness and throttle body were sent to Si-Lec for refurbishment, resulting in significant improvements, except for the idle issue. I examined the codes, which indicated issues with the MAF and air intake temperature sensors (4 and 13). I examined the intake temperature sensor out of curiosity, and it exhibited an open circuit; however, I did not assess the mass airflow sensor. The replacements arrived a few hours prior to the holiday, so I installed them, cleared the codes, and we departed!
Regrettably, it has had no impact on the indolent. The engine initially operates normally at both hot and cold temperatures; nevertheless, it occasionally revs to 2000 RPM after running for one minute while cold. It occasionally has a slight surge while stationary, which is somewhat unsettling in an automatic vehicle. Occasionally, it may stall when shifted into drive; however, once it is no longer idling, it operates smoothly and possesses ample power. It underwent servicing a few months prior to my acquisition, and I observe that it has new spark plugs and ignition leads. I replaced the coils after one terminal detached during harness removal, and I have added a bottle of injector cleaning to the system.
Preliminary study conducted during my absence indicated that the fuel pressure regulator may be the source of the problem. I have placed an order, but I am now uncertain. I re-examined the codes, and the initial MAF and temperature sensor codes had reappeared, accompanied by code 8 - 'Altitude pressure signal from ignition control module is irrational.' I observe that the SRS light intermittently flashes when temperatures are low.
Additional research indicates that the OVP relay may be responsible for the idle issues; however, could this also be the source of the error codes? Any assistance would be much appreciated!