pulled the battery last week on my 2006 to install a new cable to get Aux input for my stereo. After reconnecting the battery the car just wont stop with the typical dropping idle behaviour following a battery disconnect. I have had the battery disconnected multiple times and every time it relearns the idle fairly quickly, but this time it just wont. I have driven around 400 miles in mixed conditions over five days since reconnecting the battery and every time I hold the clutch down or put it in neutral the revs drop down to about 500rpm, shudders and goes back up to around 850 (and often keep ‘bouncing’ up and down). It doesn’t cut out on my, but it is really starting to be irritating, especially in bumper to bumper commuting.
Whats your advice, is there any extra trick in the book to try or should I remove and reconnect the battery to reset the system and let it ‘learn’ from scratch again?
Hi, I had this a while back? the solution, for me at least, was to disconnect the battery again and make sure the clean clamps were fully on the clean battery posts (bit of emery paper worked a treat here) and also ensure that the clamps were absolutely as tight as they could be? I thought they were secure previously, everything worked but the car would not settle down. Once I refitted the terminal clamps properly, I have had no further issues. Got to be worth a try? only took a few miles and car was behaving normally.
Thanks for all replies, sounds like I will give it another chance to re-learn from scratch by disconnecting the battery. Is it enough to just leave it off for a few seconds or does it take longer for the memory to fully clear?
I’m watching this very closely as I have exactly the same issue. Following a drained battery I had to jump-start my 2006 Mk3 and got the ‘bouncing revs idling’ syndrome.
With the clutch in or out while coasting in traffic the revs bounce between 500 and 800rpm.
I’d read elsewhere about the need for the engine to re-learn the idle which you can re-train by holding the revs at 3,000rpm for a few minutes until she drops back to idle.
I did this, but no joy. New battery installed as well but also no joy. About a 10% drop in fuel economy too.
I’ll check the battery terminal connections and give them a clean as suggested, but wondering if the fault could be something else.
I think I saw something on the FB site about a possible coil pack fault? Could this be the solution?
Getting a bit worried now, tried disconnecting the battery with engine cold yesterday night. After 10 minutes with the battery off I reconnected and started and let it idle for 20 minutes, now 90 miles later with all possible kinds of driving done it still keeps dropping too low and bounce between 500-1000 or so every damn time I drop the clutch. Only thing I can possibly think of that could have been wrong is that I did start the engine before first just turning the ignition on without staring to turn the wheel fully from stop to stop to turn off the traction control warning. Instead I started it and turned the steering wheel with the engine running, but I cant imagine that having such an effect?
I seriously doubt a bad battery or connection is the case as it was working perfectly fine before disconnecting the battery some days ago, no hints of weak starting power and the battery terminals are all looking nice and clean. I changed the battery for a new one about two-three years ago.
Will make another try tomorrow and see if I can polish up the terminals a bit before reconnecting, but after that I don’t know what to do if it keeps hunting
I am having this exact same problem at the moment.
Battery died outside the shops last week and had to jump start it to bring it home. Bought a new battery for it and fitted it and left it to idle for 30mins with a few trips round the block during that time. Still has the issue of dropping to low revs, like you say, when slowing down. Seems to be getting slightly better but still not what it was like?
How can the battery change affect it that much? I will try your advise about the terminal clean tonight and also take it for a big spin Sunday. Hopefully it will sort itself after that.
did a third reset this Friday from cold and cleaned up the battery connection in the process. Sorted out the traction control reset without starting the engine and left it to idle for 20 minutes without any auxiliaries running before setting off. I have now done almost 400 miles on this trial and the idle is still not sorted. It sometimes seem to almost work, then next time I drop the clutch it is back bouncing around, but I think it is better than it was before this reset. I will just leave it for a while and see how it does in a week or so. I drove from Cambridgeshire to Liverpool and back this weekend and the result was around 36 mpg with some bumper to bumper driving on the M6 so no disaster with regards to economy.
Credit to Turbo Pete for this post from 2 years ago, I followed these instructions and it planned out exactly as described below (although I did use my foot ?? ):
If the battery has been disconnected you need to re set the ecu.
Start engine. Use a peice of wood to hold the throttle down so that it holds 2500rpm. Then leave it running at 2500rpm. Don’t try doing it with your foot as small movements in your leg muscles will spoil the process. After about three minutes the engine revs will suddenly drop down to normal idle event hough the throttle pedal is held in place. At this point the ECU should be reset.
You will also need to turn the steering wheel fully to the left and fully to the right after a new battery as the car needs to re learn the full left and right lock of the steering.
Until you do this the traction control light remains on.
Hi all I have been following this post shocked as just how much hassle a change of battery on a Nc can be was thinking of changing my battery as been on awhile now , I think I will just leave thing til it is in for a service and ask them to sort it I think I would have took to a specialist after 2nd attempt cannot mess about with ECU and electrics sometimes let an expert sort if having problems our 5,s are far too precious my knowledge is basic so I look to others when in doubt … Hope you get it running at its best very soon regards Richy aka Top gun
Car continued to behave badly so took it to a good local independent mechanic that ran it through two different diagnostic computers without finding any obvious errors on their systems. Obviously they couldn’t say what was wrong, but suggested cleaning the throttle body could help. Reading up a bit on various forums it made sense to try. I was about to travel outside UK for some time so left it and upon returning this past weekend it still behaved like crap so booked a time to have the throttle body thoroughly cleaned (booked in for next Thursday). However, yesterday after picking up some throttle body cleaner thinking I can at least have a poke around without taking it off the engine fully the damn car started to behave almost like normal driving back from the shop! Revs a tiny bit unstable, but they did not drop below 750 for over an hour driving in mixed traffic. We shall see how it behaves in the coming days, but maybe the threat of ‘surgery’ scared the damn thing straight?!
Will keep reporting until it is solved or car scrapped…
I hope its now sorted. For the record I had this problem after changing my steering wheel, battery was disconnected for about 20 mins, took about 20-30 mins of varied driving before it settled to a steady tickover
I had this and tried the “drive it until it sorts it out” method for 300 miles and nothing. So I went for a drive to warm the engine, disconnected battery for 15 mins, cleaned terminals, reconnected battery. Started the engine did the lock to lock reset, then used the piece of wood to hold 3000 revs for 3 mins, then left it to tickover for 20 mins. Went for a drive and it was perfect tickover at the 1st junction 300 yards down the road.
