Funny idle

[JasonMc]

Hi all,
I noticed a funny idle a couple of years ago, and just the last few day I have noticed it again.

Idling at a set of lights and the rpm increases slightly and get a bit of a surge like you get when the aircon cycles but not as large.

I checked it in the drive way rpm increases from 650 to 700.

It is also accompanied by a change in idle sound, sounds almost metallic.

I also double checked if the voltage fluctuates during, which it doesn't, thought maybe the alternator is loading the engine. It only last for around 20-30 seconds then goes back to normal idle.

Will also add I am using the resistor mod for the EGR in case it is related.

Any ideas to what's going on?

[Lakey]

My idle fluctuates like that also. As far as I'm aware it always has. There is a sound like a solenoid clicking in and out as it changes revs. I've assumed it is normal.

Lately however on start up (when cold) intermittently I've been getting a much louder metallic rattle that only lasts a minute or so. Have been trying to record the sound so I can take it somewhere to have it looked at cause it's no use leaving it even overnight because it's erratic.

[JasonMc]

Thanks for the reply, it's good to know it might be normal.
When I have some time I'll see if I can identify if it is activating a relay, and which one.
It must be something that puts a load on the engine to increase rpm.
Makes me think it has to be alternator related.

[old Jack]

Thanks for the reply, it's good to know it might be normal.
When I have some time I'll see if I can identify if it is activating a relay, and which one.
It must be something that puts a load on the engine to increase rpm.
Makes me think it has to be alternator related.

Hi Jason,

It will not be alternator related as the Challenger does not have a Smart Alternator fitted like the Gen 4 Pajero.

If your A/C is switched ON when you start up you will get rpm fluctuation and relay clicking sound of both the A/C Condenser Fan relay and the A/C Compressor Clutch relay.


OJ.

[Lakey]

I might need to try turning off the air before starting to see if it stops my random noise issue. Might be able to discount a possible cause at least.

[JasonMc]

It is definitely not the ac. And it isn't like that from start it'll will start 30-60 seconds after start up and randomly after driving for any length of time when idling.
OJ how much variation in voltage is expected for a standard alternator?
I see between 12.7-14.2 on the ultra gauge.

[old Jack]

It is definitely not the ac. And it isn't like that from start it'll will start 30-60 seconds after start up and randomly after driving for any length of time when idling.
OJ how much variation in voltage is expected for a standard alternator?
I see between 12.7-14.2 on the ultra gauge.

12.7 to 14.2 is a good range for alternator voltage.
Factory idle specification is 650 +/-50 rpm.
The 4D56 engine is a noisy engine at idle, especially when cold.

Does the problem only happen at idle or can you see and feel rom fluctuations when driving at 1500rpm to 3500rpm?
If the problem only happens at idle does it do it in Park, Neutral, Reverse and Drive if it is an Auto.
If it is a Manual does the problem occur when the clutch pedal is out and in neutral or when clutch pedal is in and in first or reverse gears?

OJ.

[itsamitsi]

I think it's an injection learn or something along those lines. Mine does it too.

[old Jack]

I think it's an injection learn or something along those lines. Mine does it too.

The engine will automatically do an injection relearn from time to time, I have never been able to pick when it has happened but my brother had a 2011 Triton and his regularly did it and was very noticeable. Only diffence we could think of was he used what every diesel was availble since he lives in a rural area and I use BP Ultimate exclusively exempt on troops where I cannot get premium diesel. I can feel the difference in how the engine runs when it is not on premium diesel.

OJ.

[JasonMc]

The engine will automatically do an injection relearn from time to time, I have never been able to pick when it has happened but my brother had a 2011 Triton and his regularly did it and was very noticeable. Only diffence we could think of was he used what every diesel was availble since he lives in a rural area and I use BP Ultimate exclusively exempt on troops where I cannot get premium diesel. I can feel the difference in how the engine runs when it is not on premium diesel.

OJ.

This could be it, I recently went from Caltex to BP for a few tanks to see how it went, back to Caltex now and is when I started to notice it again.