[wallace94]

Hello,

I have a 2013 1.6 diesel i30 blue drive which I bought second hand 4 months ago (in the winter). Since I bought it I noticed once on startup that it was idling rough for approx. 30 seconds i.e. like it was going to cut out and abruptly stopped after this time and normal idle resumed, this happened very infrequently. However this has become a more persistent problem in WARM WEATHER interestingly as the idle rpm is lower on startup.

This problem is not exclusive on startup and will sometimes happen after the car has been driven, same symptoms however not as noticeable. It will happen with the A/C on or off, it doesn't affect it seemingly.
I have scanned for fault codes multiple times and there are none .
A local mechanic could find no problem which leads me to believe the problem is electrical.
There is no unusual smoke from the exhaust.
There are no problems while driving. I have taken off while the car is idling poorly and driving isn't affected.
I cannot see/hear any vacuum leak.
MAF appears to be working correctly (~10g/s on idle).
I use good quality diesel from verified stations.
Car was serviced recently and has new air/fuel filters.
I have watched the radiator fan to see if it was linked to that cutting in but does not appear to be. 

I am aware this is may be an unusual problem as it is so specific and am posting here mainly in the hope someone has had the same issue and can recognize the symptoms rather than expecting people to work this out from scratch !

Like I said the appears to be an electrical problem of some sort but am at a loss as to where to start looking and how to go about diagnosing and am reluctant to go to a hyundai garage for fear of being hoodwinked.

Any input is greatly appreciated. I will try upload a video if I can get the correct format

[nzenigma]

" reluctant to go to a hyundai garage for fear of being hoodwinked"    me too 

Three questions;

How many miles/ Kms has the car done?

Are you watching the Tacho ?  Rev fluctuation?

Do you have enough experience to hear an engine miss? eg. a cylinder that is failing.

[sundiz]

Might want to hook up multimeter to battery at start up. Current clamp to glow plug rail wire would be better. I noticed very ruff idle at start when I got new working glow plugs. Engine does after glow for approx 30s when started. This sends about 30A to glow plugs even when the engine is running. That puts extra load on alternator which can make the idle litlle bit rough. After glow stopping the idle gets smoother.

I noticed this after the change in warmish weather. In cold the idle is rough by nature and "disappears".

This would not explain the ruff idle with warm engine, but there might be something draining power from alternator. Might want to put all electrkc stuff on and check if the idle gets rough (glass heater etc).

[nzenigma]

I waiting to hear if all four cylinders are up and running. Could an injector misbehaving.

[wallace94]

The car has 107,000 I'm on the clock.

Yes when the rough idle happens the tachometer fluctuates, it seems to drop and immediately correct itself and that happens repeatedly for about 30s to a minute. It idles around 700-800 rpm and is very noticeably fluctuating.

I probably don't have that experience, I have had a car with failing fuel injectors so I know what that feels like and it doesn't happen with this car. I've gone for long motorway spins and have floored the throttle a few times to test it out and have had no issues, the problem seems to be only on idle that I can tell.

[wallace94]

Glow plugs is interesting, I hadn't thought of that. Should that happen after the car has been driven and let idle though ? Thought glow plugs only activate on startup.
I'm currently trying to get my hands on a current clamp and will post again if I have any more info.

[sundiz]

When current is drained, the idle should be still "smooth", engine just has to work a bit more while it is under bigger load. No fluctuating in rpm.

[nzenigma]

Easy way to prove the glow plug drain theory  , just pull out the fuse.

Hot idle at 700-800 rpm ????  normally 680 rpm -700 rpm

[wallace94]

Easy way to prove the glow plug drain theory  , just pull out the fuse.

Hot idle at 700-800 rpm ????  normally 680 rpm -700 rpm

I've been monitoring the idle all week and it's consistently at approx  780 when hot and starts above 800 when cold. Outside temp has been 10-20 Celcius. I've noticed also that when the car was idling poorly when hot the MAF reading was approx 5g/s and when it righted itself after a minute or so the reading immediately changed to 10g/s.