Idle issue

[Ninja636]

I've got a B5 1.8 (non-turbo) that has developed a problem with not being able to idle anymore. It starts no problem but you have to keep revving it to keep it running. Drives fine otherwise. As soon as the clutch goes in, the revs drop and it stalls.

I've taken it to a mechanics who gave it back after a week saying the didn't know how to fix it. They ran diagnostics on it and everything appeared to be normal. They said they think it is an electrical fault somewhere.

There is another issue with the battery going flat randomly. It can be good for a month and start every day, then one day it is completely flat. Jump starting it from another car will get it going easily and it will be fine after this for another random length of time between 1 day and 1 month. I'm not sure if these 2 problems are related or not. The battery is only 6 months old and I have been assured that the battery is not at fault.

Has anyone got any idea to what the problem might be?

[737-800]

The only way you can be sure about the battery is to swap it out for another one. I had the same problem with my battery, some times the plates in the battery can short out internally due to vibration or shock caused by normal road use ( potholes etc )

[lucianus]

mine has just the oposite. when i start it, it idles at around 1100 rpms for about 5 mins then it drops at 800-900 rpms like its supposed to. i have scanned it with vag-com and i get those errors:

17972 - Throttle Actuator (J338): Under-Voltage during Basic Setting
P1564 - 35-10 - - - Intermittent
17967 - Throttle Valve Control part (J338): Fault in basic settings
P1559 - 35-10 - - - Intermittent
00561 - Mixture Adaptation
15-10 - Adaptation Limit (Add) Not Reached - Intermittent
17978 - Engine Start Blocked by Immobilizer
P1570 - 35-10 - - - Intermittent
16502 - Engine Coolant Temp. Sensor (G62): Signal too High
P0118 - 35-10 - - - Intermittent