Q Why is the engine idling higher than normal?

I noticed, while parking our ’van, that the engine idle speed was a bit high, about 1,250rpm, but when the brake pedal is depressed it dips to normal, about 800/900rpm. This has happened on a number of occasions after a short drive following a few weeks when the ’van stood unused. Strangely, though, when I turn off and restart, all is back to normal.

Is this indicating something is beginning to go wrong? Could it be something to do with the alternator charging, earth strap or possibly the battery? I leave the ’van – a 2015 Majestic Accordo 105 with a Peugeot Boxer 2.2-litre 150bhp – on permanent hook-up and it has a S&F Battery Master.

Have you any advice or suggestions why this is happening?

Stuart Carley

AI am not as familiar with Peugeot vehicles as with Fiat, but I can’t imagine that the architecture of the electrics will be that different.

Normally, when the vehicle ECU has detected a less-thanideal battery current during start-up (below a certain threshold, it will just refuse to try to start), it will monitor the output from the alternator and, if necessary, increase the revs a little to increase the charging rate and top up the battery more quickly. Because of the shortness of the recent journeys, it may have stored some events as ‘failures’ to top up the battery adequately.

There is also a strong possibility that the ECU was getting ready to perform a DPF regeneration and you put a stop to that by applying the brake pedal. You don’t normally notice a regeneration while you are driving because you are above idle speed and cruising most times, but the ECU may have noticed increased ‘clogging’ in the DPF due to the short journeys and needs a longer run to perform this.

If the battery voltage was too low, the ’van wouldn’t start and, if there was a problem with the charging system, the dashboard battery warning light would be on and the revs would be higher all the time while the ECU tries to compensate. If there was a problem with the engine earth, the symptoms might be similar to what you have seen and therefore it is worth checking.

First I would get the engine started and use a multimeter to measure the voltage between the earth point and positive (jump) terminals under the bonnet. It there is less than 14.2V there, I would suspect the earth cable is at fault. If you see the more typical 14.4V, there is nothing to worry about.

The next thing to do would be to take it for a good 20 to 30-mile run. This would ideally be outside of city traffic and a dual carriageway at about 50mph would be ideal. The engine needs to be thoroughly warm before the ECU alters the fuelling and makes it a great deal more warm, so that a regeneration can take place.

If, after this, the increased revs at idle is still happening, the vehicle will need to be plugged into a diagnostic device to see what clues can be discovered.

Best to rule out the obvious first.

Nick Fisher