Revs going up when sat in traffic

[Janney]

I have a Ford Fiesta, 62 plate and I know nothing about cars.

However, I pay attention to what it's doing and over the past few months the engine has sounded louder when sat in traffic/ waiting at light etc.

I have noticed that the revs needle goes up and down with the noise... I'm not even touching the accelerator but it suddenly revs and goes up. What is the issue and should I be concerned? The blokes in the garage don't seem that bothered about it

[Cal844]

It will adjust fuelling as needed but the revs should stay the same, maybe a 10 to 20 rpm variance when warm.... until you use the gas. 

 

The issue can be alot of things, get it code read at a better garage 

[Janney]

Ok, thank you Cal844. What is 'code read' though? 

Also, while you're on it, the battery light has just started coming on intermittently... mostly when stuck in traffic today. New alternator before Christmas (because it all cut out - no radio, no lights, no power steering), new battery yesterday. Could there be a link? 

[billyboy]

You don't say by how many revs. It's normal to go up and down slightly, 50-100 revs, if you have the aircon switched on as it kicks in and cuts out.

[DaveT70]

8 hours ago, Janney said:

Ok, thank you Cal844. What is 'code read' though? 

Also, while you're on it, the battery light has just started coming on intermittently... mostly when stuck in traffic today. New alternator before Christmas (because it all cut out - no radio, no lights, no power steering), new battery yesterday. Could there be a link? 

If the battery light is coming on that means the alternator is not working correctly and not charging the battery.

[TomsFocus]

The revs are increasing to try and charge the battery.  Basically, the faster the engine revs, the more power the alternator produces. 

Hopefully it will settle now you've had both the battery & alternator replaced - unless there's another charging fault.

 

Also, you don't mention whether petrol or diesel?  Diesels do this when they're performing a DPF regen, but I'm assuming yours is petrol anyway.

[Janney]

Thank you for the replies.  

Yes, it is a petrol... never thought about that detail being important.🤦‍♀️

I don't know quite how to measure the revs. Are there 1000 revs between each number on the dial?? If so, it can sometimes go up about 500 revs - it looks odd and never used to do this.

No air con in use at the time - I've always been able to feel the strain that puts on the car (along with heated window). 

[TomsFocus]

10 hours ago, Janney said:

I don't know quite how to measure the revs. Are there 1000 revs between each number on the dial?? If so, it can sometimes go up about 500 revs - it looks odd and never used to do this.

Yep, that's right, each 1 on the rev counter is 1000rpm.  I'd expect it to rise to around 1,100rpm if its trying to charge.  If it's going up to 1,300 or more, that would be unusual and possibly a symptom of another problem.

[Janney]

Thanks TomsFocus... it's back in the garage today.

It can go from 1000 to 1500 when stationary. I hope it can all be fixed 

[wilkinson]

Had an XR3i which did this. Turned out to be a faulty "idle speed control valve".  Not sure if this is relevant to your car ie.  if they have a similar control valve on yours - but worth an ask at the garage.