car battery & system problems,plausible?

Could you possibly surmise where a voltage spike may emanate from? The suggestion the hall sender damage was from one seems likely as this description suggests.       ...Hall Sender works by creating a signal as the shaft of the dizzy spins. It feeds a signal back to the ECU telling it which cylinder is approaching the TDC position and the ECU then uses that information to trigger a host of actions at that moment in time. Hall Sensors are usually quite reliable (hence the reason they were used) but we do know that they fail due to age (they start to physically break into pieces inside the dizzy). They can also be damaged by voltage spikes, a classic example being when someone takes all the spark plugs out and spins the engine without grounding the king lead from the coil (HT lead). A visual inspection might show physical damage inside the dizzy itself?..... In some effort to rule out this and at the same time get the immo/ecu checked. Where a spike could be from.

As aforementioned, bad grounds, batteries, connections... Otherwise usually relays and other inductive components (motors, IgCoils, etc). As to ungrounded splugs causing damage, I doubt it though they can damage ignitors - or could in older vehicles. If it is a hall sensor that feeds the ECU, such a spike would have to go from the IgCoil thru the ignitor thru the EU to the hall sensor. But systems like Delco have the sensor circuitry and ignitor in one package which also handles the ECU supplied timing signals. But they afaik use reluctors, not Halls. So is your "Hall Sensor" a sensor module only, or include the ignitor (that feeds the IgCoil?

Known problems on that engine:- Petrol: Poor quality coil packs, prone to none starting. Diesel: Dual mass flywheel breaks, causing clutch damage. Fuel pumps and injectors fail. Both: Transmission (auto) failure. Endemic amongst ALL VAG types; ECU failure. Check with "honestjohn" UK.

Thanks...the likelihood of more than one thing wrong IS more likely. My van from ecu is to transformer(coil) then hall sender, AND the ecu is supposedly good! value rarely bad...speculation is wild. So far with all the new replacements and sensors that could be bad I am no closer to really knowing what its exact problem is. Hopefully this is the last of it. Alternators been out and waiting to be multi tested, brushes good...

What makes you say "the ecu is supposedly good" (& rarely bad)? And who is telling you this? IMO it's obviously more than one issue unless it is the ECU as I have previously mentioned (assuming sensor-ECU-ignitor). If it is, the only guaranteed fix is to swap ALL relevant parts. I usually recommend that instead of buying another working model of the same and swapping battery, alternators, all wiring looms & all electrics that they simply keep the "new" working vehicle and scrap the old. People used to do the old external alternator-regulator runaround - ie, replace what they thought was faulty (eg, alternator) only to find it was the regulator so they replace that but find the faulty regulator blew the alternator so they replace both only to find it was a bad ground to the regulator that caused the problem in the first place - so THREE sets of new alternator & regulator are expended to fix a SIMPLE connection problem. (The irony being that if they instead replaced the older external regulator system with a new integral type, they won't have that problem; they'll have simpler and cheaper future repairs, and they'll enjoy far superior alternator/electrical performance - & probably with higher alternator capability.) Now if such a simple "free fix" alternator problem causes so much time & expense, imagine such a novice with an entire computerised multiwire multiconnector multi-peripheral system! (Blown OC transistor in the A09 address line? LOL!) DIY repairers are usually the best friend of industry repairers and parts suppliers - the expanded or repeated damage or expense by DIYers often outweighs the loss professionals have due to competent DIYers. But I commend your exploits. It's nice to have the unessential vehicle and budget to be able to DIY fault find using trial & error. (Tho I admit I'll usually research - sometimes due to laziness, but usually because I hate waste - & prefer to spend my money or time elsewhere. Besides, I'd probably want to DIY replace rather than DIY fix something that IMO is inferior of prone to problems or subperformance.)

Nice post Peter and did mention poor earths on Mkl and Mkll Golfs, transporters etc. OP make sure you have good clean corrosion less connectors.

Yes, the bones of it in simple checking for me. Most info comes from trawling the net and the post said its "uncommon for the ecu to go, more durable than ..." another car.I remember that one, said it was more likely the hall sender etc. this problem wraps itself around other similar problems so I dismissed it and got new parts. I've just ordered in the air flow sensor because a post identified it to be the reason for erratic idle, but the test for it gave vagcom the hand to see it drop in temperature when a substance drove the temp lower, then watch it rise, it showed it works! but without doubt if it errs then the ecu errs and sends erred info about- this is also the lambda o2 area, so assumingly the REALLY the broken part, until later I change the coolant sensor which contributes to the same problem..differently, leading to errors from reading sensors, from ecu. A circle of it. Today the new hall sender arrives and many more days of testing before I even start it. Will get back if some electrical info is needed. Thanks.

Yes well, "they" are contradicting us aren't they? And tho you may get tips. you still have to check (see my last reply - and was it this thread where I thanked whoever replaced ALL ECU peripherals (including the complete distributor!) so I could grab them all at ridiculous prices when the car hit the wreckers? A few $hundred worth for well under $100 - and that included the wiring loom. (Why do people spend $thousands of aftermarket EMS systems when they can have a complete and most often superior set up for a few $hundred?}.) Idle could be the idle air motor (if fitted) as well as manifold temperature and all pressure sensors, plus fuel pressure & pump, dirty injectors or fuel or air filters, valves or clearances, splugs, etc etc. But I'm merely repeating the same old info... I won't be able to help you further. Except for an in person visit, I've given all I can. Like I said, take it to an auto electrician. Or if you really want to DIY, then do a proper analysis and determine the problem before buying parts.

An update, the single pole trigger only gives 0.14v when key turned on and ignition on it just stays, the 'cleaned' starter motor won't work now, did have clicks from the relays when turning the key so I re-tuned the position of the magnets to central position for better rotation and now it won't click anything. It should be 12.7v. I guess its somewhere from fuse/relay,immo,ecu and wires. Replaced ignition switch ,30relay, fuses look good....would immo or ecu be responsible for varying voltage? There are so many posts that contradict but I just sort which is more viable.

Agreed. I've said "find" before buying. Halls don't burn - if an HKZ type only a voltage higher than 5.5V or excess current going thru its Open Collector output transistor can burn it. But that should be "simple knowledge" with a bit of research & understanding.    I'll umwatch this thread. As I wrote earlier, there is nothing else I can offer (other than a complete course - unless enough specific details are supplied).