If you mean that the revs respond erratically to the throttle pedal under certain circumstances, then yes this problem can be diagnosed and rectified with some clarity.
If you have a misfire or generally rough running then it seems to most likely be related to the coil packs.
These faults produce a diagnostic code which can be read with a cheap OBD-II reader, and swapping the coil packs around can confirm which might be faulty. If you have a question then it's best to post it in the Mk1 GD section of the forum
To aid those doing the research for cars built with an electronic throttle body by Bosch, here is a summary of what is known about the wiring fault which typically manifests itself as an intermittent stuttery or hesitant throttle pedal response which may sometimes only occur with the car in certain positions, under certain loads or at different temperatures.
Some research indicates that the typically faulty wire is the yellow/green 5v supply to the butterfly position feedback sensor on the throttle body served to pin 1 of it's 6 pin plug at the bottom of the unit. There should be a steady 5v between pins 1 & 2 when the ignition is turned to position IG(II) and the cable loom leading to it is manipulated.
The cable forms part of the main wiring harness for the engine so is not easily removed and should be repaired in situ. The cable at the top of the throttle body is not involved and supplies a different sensor. Feedback indicates that the break is at the T junction in the conduits closest to the throttle body. It may of course be a different wire, somewhere else, or another fault entirely.
Throttle body connector (6pin) is wired to the ECM like this:
Pin Cable Function Levels when key is in IG(II)
ECM connector 3 (52pin)
4 YEL/GRN VCC3 (Voltage supply to sensor) 5v
29 GRN/BLK SG3 (Sensor ground) 0v
36 BLU TPSA (Throttle position sensor A) Throttle closed 0.1v / fully open 4.7v
49 YEL TPSB (Throttle position sensor B) Throttle closed 0.1v / fully open 4.9v
ECM connector 5 (9pin)
1 RED ETC1 (Electronic throttle control 1)
2 GRN ETC2 (Electronic throttle control 2)
The throttle pedal sensor is also wired to the ECM
ECM connector 3 (52pin)
34 GRN APSA (Accelerator pedal position sensor A) Released 0.6v / pressed 4.1v
50 RED APSB (Accelerator pedal position sensor B) Released 0.2v / pressed 2.3v
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TG
