FAQ
TL;DR: BMW E39 520i 2.2L stuck at 1200 rpm can flag throttle “A0/A1” faults; “engine throttle position controller - slightly blocked and then permanently locked.” Root causes ranged from adaptation needs to a corroded ECU harness. [Elektroda, ja3ol90, post #17001837]
Why it matters: This FAQ helps 2001-era E39 owners quickly triage throttle faults without wasting money on unnecessary parts.
Quick Facts
- Symptom snapshot: starts, idles fine, but chokes around 1200 rpm under throttle input. [Elektroda, ja3ol90, post #17008502]
- Vehicle scope: 2001 E39 520i 2.2 uses an electronically controlled throttle body. [Elektroda, ja3ol90, post #17008401]
- Fault text seen: A0/A1 throttle controller reported “slightly blocked,” then “permanently locked.” [Elektroda, ja3ol90, post #17001837]
- Attempted part swap: replacing/cleaning throttle body did not resolve the issue. [Elektroda, ja3ol90, post #17008401]
- Confirmed fix from thread: corroded and overheated wiring at the ECU connector repaired. [Elektroda, ja3ol90, post #17233929]
What do BMW E39 throttle codes A0 and A1 mean in this context?
In this case, the scan tool reported the throttle position controller as “slightly blocked,” then “permanently locked.” That points to an electronic throttle control fault, not a mechanical pedal issue. It also explains the limp-like behavior when pressing the accelerator. [Elektroda, ja3ol90, post #17001837]
Why is my E39 520i idling fine but stuck at about 1200 rpm on throttle?
The thread’s car idled normally but would climb to about 1200 rpm, then stumble and surge. That response suggests the ECU limits throttle opening due to detected throttle control or wiring faults, placing the engine in a protective mode. Clearing errors briefly changed behavior but did not fix it. [Elektroda, ja3ol90, post #17008502]
Did replacing the throttle body fix the problem?
No. The owner installed a different throttle body and cleaned the unit, yet symptoms persisted. This points past the throttle body itself and toward control, adaptation, sensor signals, or wiring. An edge case here is a damaged harness near the ECU, which ultimately proved true. [Elektroda, ja3ol90, post #17008401]
What actually fixed the car in the original thread?
The root cause was a rotted and heat-damaged wiring bundle at the engine control unit connector. Repairing the harness resolved the throttle errors and low‑rpm choking. Quote: “Rotting and over burned bundle at the control computer plug.” [Elektroda, ja3ol90, post #17233929]
Will a throttle adaptation help on a 2001 520i 2.2?
A contributor recommended performing a throttle adaptation as an initial remedy. Quote: “Throttle adaptation. Should help.” It is a low-cost step after battery disconnects, throttle swaps, or cleaning. If it fails, proceed to wiring and signal checks. [Elektroda, kwiatek73, post #17124060]
Is the 2001 E39 520i throttle electronic or cable-driven?
For 2001 520i 2.2, it is electrically controlled. The owner confirmed electronic throttle and had already swapped that assembly during troubleshooting, which narrowed the fault away from the physical throttle body. [Elektroda, ja3ol90, post #17008401]
How does the car behave after clearing the throttle error codes?
After clearing, the engine briefly revved to about 2000 rpm and surged but responded to the pedal. That transient change indicates the ECU temporarily resets learned states, yet the underlying fault quickly returns. This is typical when the root cause remains unresolved. [Elektroda, ja3ol90, post #17001837]
Should I check fuel pressure or the MAF before blaming the throttle?
Yes. A helper advised inspecting the intake path, temporarily unplugging the airflow meter, and checking rail pressure. These fast checks can distinguish airflow or fueling issues from throttle control faults, preventing misdiagnosis. [Elektroda, mateusz19896, post #17008564]
Do I need BMW-specific diagnostics like INPA or DIS?
Using INPA or DIS helps watch live parameters, pedal tracking, and sensor responses. The helper emphasized observing smooth pedal resistance values and probe activity. Generic tools may miss BMW‑specific data and adaptations. [Elektroda, mateusz19896, post #17008555]
What about oxygen sensors if the car has LPG?
The owner noted O2 probes appeared disabled on LPG, with no change when testing. That reduced immediate focus on mixture control and shifted attention to throttle control and wiring integrity for this case. [Elektroda, ja3ol90, post #17008502]
Can wiring cause throttle A0/A1 faults even if the car starts fine?
Yes. The car started and idled well, yet damaged wiring near the ECU caused persistent throttle errors and limited rpm. Electrical faults can selectively impair drive‑by‑wire while leaving base idle intact. [Elektroda, ja3ol90, post #17233929]
Quick 3-step check to avoid parts darts?
- Inspect throttle inlet and ensure the blade moves freely while commanded.
- Disconnect the MAF briefly to compare behavior.
- Measure fuel rail pressure to rule out supply issues.
If unchanged, proceed to adaptation and harness inspection. [Elektroda, mateusz19896, post #17008564]
