Rare rough idle

[Vmax]

SVX is 1992, Ecutune stage 1, 4.44 swap, TCU Ecutuned, car is well maintained, but recently started to idle extremely rough ONLY in very hot days at a stop light or in traffic in very low speeds. Eventually it would stall, will not start up right after, but 10-15min later will start up normally, as nothing happened.

it would idle for 1 hour fine and then out of a sudden it would start to sputter, idle rough. If you pop up the hood it would come back to normal???

So far ruled out are:

1. MAF - tried with another one ( although not SVX ), but would do the same symptoms at idle
2. Alternator and battery are tested and OK
3. Engine codes - none, when problem occurs. Had an old one for TPS, but never came back.
4. New spark plugs, oil change and rocker cover gaskets together with spark plug 0 rings ( problem was present post and after this service ).

Any ideas or hints where to look at are highly appreciated.

Tnx

Stan.

[SubaruPartsGirl]

When you are in traffic or stopped at a light do you find that this happens when you stop very close to the person in front of you? Sometimes when you are too close to a car in front of you on a hot day the car intakes the exhaust fumes from the car in front of you and will cause a vehicle to run rough because it's not getting enough fresh air. I don't see this very often, I suppose it takes a fairly specific outside and exhaust conditions to make it happen but I do hear this complaint once and a while. It may also be a situation where something else is beginning to fail and this condition makes it worse.

I will also note that I have personally seen this issue with my tuned WRX but never in my N/A Forester, the WRX is just much more particular about driving conditions in general and doesn't run especially well when it's very hot and humid but is smooth as ever on a cooler, dry day.

[Vmax]

Thanks for replying in this thread.

Nope, this issue occurs redardless of traffic or just idling alone at the car shop.
I have swapped another alternator in today but after idling for a couple of hours voltage dropped suddenly to 11.4
Battery is 6 months old, maf is ruled out, tried out 2 different oem alternators, additional ground and power wires were ran at the test today.

Previous issues were ac door mode motor code which was fixed by replacing it, and push button ignition system unit rebuilt.

Still no code when voltage drops below 12

[SubaruPartsGirl]

Vacuum or air leak? How is the condition of the hoses? Cracked intake boot?

[oab_au]

Originally Posted by Vmax

SVX is 1992, Ecutune stage 1, 4.44 swap, TCU Ecutuned, car is well maintained, but recently started to idle extremely rough ONLY in very hot days at a stop light or in traffic in very low speeds. Eventually it would stall, will not start up right after, but 10-15min later will start up normally, as nothing happened.

Any ideas or hints where to look at are highly appreciated.

Tnx

Stan.

Stan get the injectors checked, it sounds like one of them is leaking fuel in to make it very rich.

[Vmax]

Done some more testing and we are back at suspecting the alternator - car left to idle for 30-40min and voltage drops below 12v.
Alternator was rebuilt once with a new diode block, tried with a second hand one, but still the same problem.
Can this be due to the voltage regulator failing in very hot conditions?

Harvey - when rough idle starts it is everytime affecting different cylinders - how can i check if an injector is leaking?