big problems after fitting a new car battery

Hi all firstly what a great passat forum after reading a lot off posts and picking up some great tip’s. The car is a 98/99 vw passat 1.8t 20v sport. ok my problem first started after I fitted a new car battery (I had no problems with the car until I did) then I noticed that if I gave a quick rev to the engine or coming to a stop on the road it would dip down to 600 rpm as if to stall then rev up a bit then back down then it would level out to its normal rev about 900 rpm plus under the bonnet it sounded like a lot off tapping noise which was never there before.plus on the lcd screen the mph was well out sometimes stuck .again on the lcd screen the mpg would show 24-35 then shoot up to 200 mpg then level back down . I took the car to vw and was told that after the battery is disconnected that all the learned values are erased on the ecu and all the basic settings would have to reinstate by vw .so after two hours waiting about and £60+ after two half hours it was ready but as I jumped in and started the car it was just the same the engine was erratic tick over. so it when back in today to have it done all over again and was told they do not have a clue as yet to what is causeing the problem with out having the car for a full day£££££££,on the full elec test no problems was found everything was ok no faultys .firstly has anyone had this problem after changing the battery ,plus if the battery ever goes flat again will I have to get vw to have the basic settings installed again.lastly what are the basic settings .yours thankfully Justin

Sounds like they have been telling you fibs !

The ECU will re-learn all by itself.

My advise is;

1, Disconnect the battery again for at least half an hour so any stored values are erased.

2, Re-connect the battery and start the engine. Do NOT touch the throttle at all, let it idle for a least 5 minutes.

3, Take it for a spin and try and vary the driving as much as possible. Drive for at least an hour and don't be scared to give it some welly.


If this doesn't sort it, you are better off finding someone off here with vagcom (see the link in my sig) or take it to a good independant to get it read for faults.

hi col thanks for the reply
i will give this a go tomorrow and will get back to you if it works vw will be getting yet another visit asking for a refund .iv check on your link great idea hope someone round scunthorpe will join your list.
once again thanks

I agree, these cars have well dodgy control units, they seem to get scrambled by low voltage such as a flat battery or bouncing or dragging the clamp when reconnecting a battery. Disconnect for a while and then cleanly and instantly reconnect.

Agreed, but I don't believe the ECU needed reprogramming - I guess you can't have a concience if you want to be a dealer...

I'm wondering if it has anything to do with the ECU. Is it possible any wires, hoses or sensors got disturbed whilst changing the battery?

The appearance of the tapping noise is odd; what part of the engine is it comming from? Does it vary with engine speed?

Guy

I had my battery disconnected for about 5 hours today, reconnected and everything was normal.

Think VW owe you a refund!!!!



EDIT.....

I checked a couple of things in the adaptation for the dash panel today after finding out how to change the odometer from Km to Miles......
My service interval info had reset. I cant be 100% sure if this was due to the battery being discinnected as I also disconnected the dash panel from the wiring loom yesterday, but if theres no power on the loom then I guess if wouldn't have made any difference, so maybe discinnecting the battery does reset the dash panel adaptation to defaults.
Luckily I had a copy of what the values were set to from a few days ago!!!




Nick.

I think you might want to try a 'throttle body adaption' carried out. This recalibrates the fly-by-wire throttle. This takes about 2 minutes, but requires eiither a dealer or someone with VAG-COM. The latter is probably your best bet as then you can scan for other error codes and do some live logging too, which may help track the issue.
Whereabouts are you ?

hi sorry i have not got back pc problems as well (they say it comes in three's) i did try as you said col but no joy nice ride out to the coast lol
iv got my hands on a data cable and a copy off the vag-com 4091 (limited use as it was a free download) from a friend after two hours messing about i got the laptop working with the car.came up with no ele faults it found the air con and abs system and engine numbers but thats as far as it goes.will have a play again later.cheers justin

sorry carps iam in scunthorpe

iv just clean'd the battery terminals and leads checks all the plugs round the engine and found just by chance the accelerator cable adustment clip was missing?? i was made to belive that the throttle pedal had a position sensor...vw again..yahooo that must be it :beerchug: so i put a small tie strap on ya you quess it never made any differant:confused: but i did found one thing as i moved the throttle body from inside the engine bay to rev it there is a throttle valve positioner looks like a key hole shape that when i let go moves back and forth on its own.does it have to be resting on the throttle body when it let it go as there is a about 4-5mm gap when it has stop moving about and ticking over..