VW Bora unstable idle speed after start
A driver drove me his VW Bora 1.6L car, BWG engine 2011 year, in 50 thousand miles. He said he find it has unstable idle speed after start, even flameout seriously, and has limited power.
I firstly use VAS50541 to connect the car and the computer, finally it read out trouble code: 17796／P1388035, the fault code description is: Inner control unit memory calibrate and error. Then I use Launch X431
to test, and the international standard fault code (OBD) is P2106, code description: Throttle Valve Actuator Module.
Does ECU have problem?
If ECU have problem, then at the same time many other faults also exist, so it is not ECU fault. The first step is to solve ECU harness, ground line problem, after solved the fault stay.
Replace ECU and shield harness around ECU?
Then I try to replace new engine control unit thinking it will clear trouble code. But after trial, the fault code stay, again I use Launch X431 to test, and get the same fault code. I guess the signal interference cause control unit internal error, and then I shield the related harness around ECU, but fault stay.
Then I decide to diagnose system, analyze ECU engine speed and read data stream. System Simos74 calculate the target speed according to external request ( such as: driver willing, air conditioning system, gear level)and internal speed request; next is to control engine speed according to Intake valve, ignition timing and fuel injection pulse width signal; then tell the actual speed to Simos74 by crankshaft position sensor, finally to amend.
The fault is found out:
With the above-mentioned analysis, plus the data of each component I analyzed, I find only when I quickly turn steering wheel and when the steering wheel turn to the limit, the engine data stream 55 group 4th zone 2nd place becomes 1. Finally, I confirm the steering system has fault, then I replace a new Power Steering Pressure Switch, the fault is solved.
When the steering wheel is quickly turn and turn to the limit, the load out of engine will increase. At this time, engine control unit doesn’t increase speed but reduce, throttle is out of control, fault signal pass to engine control unit. Meanwhile, Power Steering Pressure Switch has fault, also engine control unit receive the fault signal and misunderstand the signal is throttle is out of control, then memorize the P2106 as fault code and explained as inner control unit memory calibrate and error.
As for the ECU memorized fault code, if the repair man solve the trouble only by the trouble code, then it will be hard to find out where the problem locates. When we analyze, we are supposed to integrate each system working principle and other symptoms, which help quickly troubleshoot the trouble.