Running at low revs

[SPorter]

My A-Class (Manual - Petrol) has just started running at very low revs. And when I say low, I can't even see the needle when ticking over. Also it doesn't seem to be chargin the battery very well as it takes a couple of attempts to fire up in the mornings. (By the way, it's only used for short town journeys). Other than that, it seems to run fine. Is there a quick fix or is it a garage job? Any suggestions greatly appreciated.

Simon

 

[mattkh]

Hi
Which climate are you in ?
What is the mileage ?
Apart from the idling, is it stalling ?
Take it for a good run down the highway.

 

[SPorter]

Hi
Which climate are you in ?
What is the mileage ?
Apart from the idling, is it stalling ?
Take it for a good run down the highway.

Mileage is about 45K, 5 years old. Climate? South East.
No stalling.
Will try giving it a good run at the weekend.
Will keep you posted.

 

[brandwooddixon]

If the rpms aren't registering it's likely to be a sticky guage needle.

Does the engine on tick over sound as if it's labouring?

If the battery hasn't been changed in the last 5 years then it is likely to need replacement. Although saying that if the engine is continually being run at very low rpm then the alternator wont charge the battery, however, I thought that this was usually below about 400 - 500 rpm.

 

[SPorter]

If the rpms aren't registering it's likely to be a sticky guage needle.

Does the engine on tick over sound as if it's labouring?

If the battery hasn't been changed in the last 5 years then it is likely to need replacement. Although saying that if the engine is continually being run at very low rpm then the alternator wont charge the battery, however, I thought that this was usually below about 400 - 500 rpm.

Needle didn't seem sticky as when I put my foot down it moved smoothly but not as high as it should be.

Now here comes the funny part. When I started her up last night, the Revs were fine but I had 2 warning lights come up on the dash for the ABS and the Break Assist. Bit worrying on a car only 5 years old with regular services. Anyway, started up again this morning, revs fine with no xmas lights on my dash. Spoke to my local dealer and surprise surprise they can't fit me in until the new year. Have I got anything to worry about or do you reckon this is just a glitch?

 

[SPorter]

If the rpms aren't registering it's likely to be a sticky guage needle.

Does the engine on tick over sound as if it's labouring?

If the battery hasn't been changed in the last 5 years then it is likely to need replacement. Although saying that if the engine is continually being run at very low rpm then the alternator wont charge the battery, however, I thought that this was usually below about 400 - 500 rpm.

Forgot to say that battery is heavy duty and about a year or so old.

 

[jibcl500]

change the air filter.
jib

 

[SPorter]

change the air filter.
jib

Is that a quick n easy diy job? Or should I just ckeck the one I've got to see if it's ok before changing it.

 

[brandwooddixon]

Air filters are normally a 1 minute job. Open bonnet, unlip cover, remove and replace. A simple check to see if it's a blocked filter would be to remove it, replace the filter box cover and run the engine if the engine revs are faster at idle then replace the filter.

Do you think that maybe the rpm dial is reading incorrectly or do you think that the engine really is turning over more slowly at idle? There is a known problem, although not common, of needles sticking to their stops and only moving when sufficient speed is attained.

I can't say for the A-Class, but I know that some cars take there engine speed signal (for the rev counter) from the alternator. It may be worth getting the voltage across the battery checked. I think that it should be around 14V with the engine running.

I've had problems in ther past which got me worried - BAS, ESR, ABS lights coming on at startup. They were triggered by low voltage on startup, in my case a new battery fixed it, but in your case, unless the engine actually sounds like its running far slower than usual it may be alternator related - hence the voltage check.

 

[jibcl500]

We bought a A160 in May and for a 1.6 I thought it was very slow, replaced the air filter and did a service at the same time and it felt like it had doubled the bhp. The filter is really small on the these cars, I make a point of changing it every 5k.


jib

 

[SPorter]

Thanks for your input guys. Will check the filter this weekend and hopefully that will cure it. Can do without spending any more money over xmas!