E-Gas Throttle Control

The Bosch Motronic ME7.5 system replaces mechanical throttle cables with a closed-loop electronic throttle control system (DVE — Drosselklappe Elektronisch / E-Gas). The throttle body housing incorporates a high-torque bidirectional DC electric motor (G186), a dual-spring fail-safe mechanical return mechanism, and two inversely paired angular potentiometers (G187 and G188).

When an engine builder replaces the factory 60 mm throttle body with a larger unit (such as the 70 mm Audi S4 2.7T / R32 VR6 throttle body or a 75 mm Porsche unit), the fluid dynamics and servo motor characteristics diverge substantially. Failure to recalibrate the DVE parameters causes hyper-sensitive "hair-trigger" pedal response, erratic idle hunting, and throttle limp-home mode.

code

┌──────────────────────────────────────────────────────────────────────────────────────────────────┐
│                   BOSCH ME7.5 DUAL-POTENTIOMETER CROSS-CHECK SAFETY GEOMETRY                     │
├──────────────────────────────────────────────────────────────────────────────────────────────────┤
│ Voltage (V)                                                                                      │
│      ▲                                                                                           │
│ 5.0V ┼──────────● (G188 Rest)                                       ● (G187 WOT)                 │
│      │           \                                                 /                             │
│ 4.5V ┼────────────●                                               ●                              │
│      │             \                                             /                               │
│      │              \                                           /                                │
│ 2.5V ┼───────────────X───────── Mid-Point Intersection ─────────X                                │
│      │                \                                       /                                  │
│      │                 \                                     /                                   │
│ 0.5V ┼──────────────────●                                   ●                                    │
│      │                   ● (G187 Rest)                     ● (G188 WOT)                          │
│ 0.0V ┼───┴───────────────┴─────────────────────────────────┴───────────────────► Throttle Angle   │
│         0° (Mechanical Lower)                           82° (Full WOT)                           │
│                                                                                                  │
│ Continuous Safety Sum: V(G187) + V(G188) = 5.00V ± 0.20V across 100% of plate travel             │
└──────────────────────────────────────────────────────────────────────────────────────────────────┘

22.1. Dual-Potentiometer Plausibility & Mechanical Limp-Home

G187 (Potentiometer 1, Pin 33): Primary throttle position feedback. Output voltage rises linearly from 0.50V (closed) to 4.50V (wide-open throttle).
G188 (Potentiometer 2, Pin 34): Inverted safety monitor feedback. Output voltage drops linearly from 4.50V (closed) down to 0.50V (wide-open throttle).
The Golden Safety Law: VG187 + VG188 = 5.00V ± 0.20V
Limp-Home Failsafe: If the sum deviates by more than 0.20V for longer than 60 ms, the safety processor assumes sensor wear or wiring short-circuits. The CJ220 driver H-bridge is instantly tri-stated (power cut). Internal dual return springs pull the throttle plate to its mechanical rest stop (6.5° to 7.5° plate opening), limiting engine speed to a maximum of 1500 rpm with zero pedal response.

22.2. Fluid Dynamics & Cross-Sectional Area Scaling

THROTTLE BODY UPGRADE CROSS-SECTIONAL COMPARISON

Throttle Body Model · Internal Dia · Flow Area · Area Multiplier
Throttle Body Model	Internal Dia	Flow Area	Area Multiplier	Target Flow Application
Stock Mk4 GTI AWP	60.0 mm	2,827 mm²	1.0000 (Base)	Stock to 300 bhp
Audi S4 2.7T / R32	70.0 mm	3,848 mm²	1.3611 (+36%)	Big Turbo (350–500 bhp)
Porsche 996 / Hemi	75.0 mm	4,418 mm²	1.5628 (+56%)	High-Boost 500+ bhp Setup

Why Large Throttle Bodies Require Calibration

Because flow area scales with the square of diameter (A = π r2), cracking a 70 mm throttle body by just 3.0° admits 36.1% more airflow into the intake manifold than a stock 60 mm unit at the exact same angle.

Symptoms on Uncalibrated Files:
1. Violent low-RPM bucking and jerky parking-lot maneuvers.
2. Idle surge: the idle air control loop commands tiny adjustments, but the oversized plate causes large airflow oscillations.
3. DTC P1545 / 17953 (Throttle Position Controller Malfunction).

22.3. Calibration Protocol for Upgrading to a 70mm Throttle Body

1. Rescaling Driver Request Map (`KFPED`)

Address in 06A906032LP: 0x014602 (12 × 16 grid).
Modification: Soften the initial tip-in values in the first three columns (0%… 15% pedal travel). Reduce commanded throttle angle by approximately 25% to 30% off-idle to restore smooth progressive pedal feel.

2. Recalibrating Overrun Throttle Floor (`WDKUGDN`)

Address in 06A906032LP: 0x013E08.
Modification: Lower the minimum throttle angle threshold during deceleration from stock 1.2° down to 0.8°. Because the 70mm plate flows more air at the same angle, leaving WDKUGDN at 1.2° prevents the engine from pulling proper vacuum on overrun, causing hanging revs during gear shifts.

3. Tuning DVE Motor PID Parameters

If the 70mm throttle body exhibits high-pitched buzzing or sluggish tracking:

KPDVE (Proportional Gain): Reduce by 10% to prevent motor driver over-current oscillation.
TIDVE (Integral Reset Time): Adjust to eliminate steady-state position offset errors.

4. Mandatory VCDS Realignment (Basic Settings Group 060)

After flashing the scaled binary:

Connect VCDS, select 01 - Engine.
Key ON, Engine OFF, Coolant Temp between 10°C and 90°C, Foot off the accelerator pedal.
Select Basic Settings - 04, enter Group 060, and click Go.
The ECU will cycle the new throttle plate from fully closed to fully open, saving the new ADC voltage endpoints into SPI EEPROM Pages 16–20.
Confirm that Field 4 displays ADP OK.