Audi A6 intermittent locking and anti-theft system idle instability failure

Audi A6 intermittent locking and anti-theft system idle instability failure Symptom
An original section 1996 Audi A6, intermittent locking and security systems launched after idle instability.
Troubleshooting
Before I take the car, car repair stations in other maintenance has been conducted. The process described below.
First, with the detector read fault codes: lock anti-theft system, intermittent engine failure; anti-theft system key signal is too weak presence of intermittent failures. Clear out the fault code, cleaning the idle speed motor, throttle, fault is not excluded. Also check the throttle position sensor and idle on the line and did not find the cause. Start the car, the engine starts immediately after the flame, and then check the anti-theft system is locking, the fault code cleared after normal start, but the idle is still unstable, and the anti-theft system has been intermittent failures. After repeated examination, there is no reason to find fault, help the author.
I take the car, the engine start easily, accelerate still good, idle and forth between the 1200 ~ 1500r/min swimming. With the detector reads the data stream can only be observed in idle state, a little add a little oil, the detector will lose communication with the ECU, that is no signal. Observed in the flame mode static data flow: do not step on the accelerator pedal, the throttle opening show zero, idle contact is displayed as connected, a little bit to increase the throttle, idle contact immediately disconnected, the throttle opening is also corresponding change in the number of steps the motor idling about 50 or so, the water temperature is 96 ℃, appears to be normal. Then read the fault code, display system normal, no fault. Check all vacuum tubes, also found no loss; check the fuel vapor recovery unit, is normal. And remove the air intake hose, started a direct hand to block the throttle, the engine will soon turn off, indicating no leakage phenomenon. Remove the throttle body has been washed very clean, observed when it is closed tight enough, there is no possibility of leakage. Adjustment screw has no passive, and the normal position. Measuring idle contact, good contact, open and close properly. Test throttle position sensor, also normal. Also remove the idle speed motor, observed in the open when the ignition switch is apparent retraction, turn off the ignition switch will recover, so it seems idle speed motor and control circuit should be no problem. In the disassembly process of careful observation of the idle air flow path. Start the engine, and immediately turn off, is the anti-theft lock again. In this process, we found anti-theft light will turn on the ignition switch off properly, but when you start the engine anti-theft light will light up. With the detector into the alarm system, there is a fault code: "ignition key signal is too weak," the intermittent fault. After clearing the engine can be started, and repeated measurements related to the line security systems, not bad and so on, still nothing.
I carefully analyze the failure phenomenon: Every time we turn the ignition switch off when the security lights are able to illustrate the key can be correctly identified only when the security light will start Qiliang. Taking into account anti-theft system trouble-free line, and each alarm lock, the repair time are longer, consume more power in the case occurred, is suspected of starting the motor when the voltage drop is too large, causing the anti-theft locking system . Then measure the voltage at startup, only about 7V, and then test the battery voltage is basically the same, immediately with an auxiliary battery in parallel connection, and then start flashing theft light is not the phenomenon, the engine is working properly. Parking auxiliary battery state disengaged, the measurement voltage is 12.8V, but as long as an open headlamp, the voltage quickly drops to 11.3V or so, and then start only when the voltage of 7V or so, and then we will be locking security. When turn off all electrical appliances, place for a while, the voltage will rise a little, you can also start up. It finally found the reason here is that the battery performance can no longer work, and need to replace the battery.
Then check with the relevant part of idling. After starting the engine idle speed motor hand block air intakes, engine flameout, part of the fault appears to be controlled, because it shows all the engine is idling the intake are the motor inlet access. As the idle speed motor to stretch, there is no line fault. There may be idle motor catching and can not be completely stretched out, causing excessive idle speed and ride. Again remove the idle speed motor, simulation work, is fully capable of normal full scale, and properly sprayed some lubricant, install back, the fault is still not ruled out. To verify that you can artificially control the idle speed, so the idle hands to block the inlet part of the motor (to reduce the air flow rate). Suddenly stable idle time, and with the block size of the inlet, idle stability changes. Further reduce intake, idle only 300-400r/min, the engine still running stable. Gradually increase the feed rate, idling also increases, but the speed increases to reach a certain level, no further increase of gas flow speed is increased. Completely open, the engine idle speed is still not increased, completely normal, only 700r/min. Turn off after the start, remained stable idling, improved idle speed after the open air about 100r/min. However, after replacing the battery, the engine idle speed has increased to 1200r/min, and stability. So they adjust the idle speed with the manual method, again adjusted, normal idle speed immediately. This process is off to learn. And start over several times, the engine were operating normally, troubleshooting.