Hi,

I noticed an interesting behavior and a metallic/rustling sound after a cold start.

This happens when the car has been standing for a longer period of time, for example overnight.

The issue does not occur after shorter stops, such as after a workday of about 8 hours.

It requires a longer standing period.

When the issue occurs, the revs drop quite quickly after starting to around 1000 rpm or below.

When giving some throttle and then letting off, a very unpleasant metallic rustling noise can be heard.

If I turn the engine off and start it again, the revs stay normally around 1200 rpm for a while and then gradually settle to about 800 rpm.

After this restart, everything works and sounds normal again.

There are no fault codes. What could be causing this?

The video clip shows the issue.

https://photos.app.goo.gl/X81evsGHVGwE6z3g9

12 hours ago, AksA87 said:

If I turn the engine off and start it again, the revs stay normally around 1200 rpm for a while and then gradually settle to about 800 rpm.

After this restart, everything works and sounds normal again.

There are no fault codes. What could be causing this?

The video clip shows the issue.

12 hours ago, AksA87 said:

The action of a rising engine revs to 1200 is normal after multiple starts and with the headlights on. The battery charging system is replacing the energy lost in the battery and then reverts to the normal 800 revs when satisfied. It will be more noticable as the battery ages.

I cannot detect the noise you mentioned but based on other posts, it could be wear in the aux belt tensioner. Open the bonnet and listen while someone else starts the car.

Hi,

Those higher rpm´s are also because there is a secondary air pump in action at the cold start and now when cold starting first time it seems that it is not active because rpm´s drops so fast to regular idling rpm´s. It is that scraping noise that you can hear after lifting the throttle and as you can see, after turning off and starting again, everything works normally. Secondary air pump keeps the rpm´s at 1200 like it should and that scraping sound does not appear when revving and lifting the throttle. I noticed this morning that turning the ignition on, off, on again and after that starting the engine everything worked normally. Full cylinder head rebuild done 10 000 km ago and with that, every sealing, all the belts and chain with tensioners replaced. Started to think that could this be something like the starter motor for some reason stays connected to flywheel?

I think I found the problem.

It has something to do with the aircon and SAI.

AC won´t always turn on automatically and when that happens, SAI will also stay off and I think that scraping noise is coming from the AC compressor.

When pressing "AUTO" button the blower turns on and after that everything starts normally without any noises.

Something does not engage/disengage at the AC Compressor like it should.

The compressor is running all the time. The pistons travel are dependant on a signal from the controller. Imagine a tilted swash plate that can control the amount of displacement of the compressor pistons. With the plate vertical there is no pumping action but as the plate is tilted the pistons are progressively engaged more.

This a mechanical system described but the same effect can be had in electrical systems. Either way, there is no engagement clutch like the compressors of decades ago.

Your scraping noise may be a worn front bearing on the compressor.

So it is not that then. Still haven´t find the cause. Now there has been a long run without that problem. Probably something to do with the weather temperature.

It has been warmer days now and everything works good. No fault codes.