V70 2.4 Rough Idle, Stalling and Misfire problem
 

Hello, I have this problem which I cant get to the bottom of, V70 2.4 20V petrol non-turbo 02reg 185k.

symptomps:
- very rough idle, hesitation at the set off
- stalling or almost stalling when slowing down, rpm drops to below 500rpm
- when warmed up, a whining noise from the engine (like a continuous alarm siren)
- random misfire
- lights flickering on idle
- after a while of the above symptomps two of the ignition coils failed (no1 & 5)

Faults:
- ECM-912A - Engine Control Module (ECM) communication Faulty Signal
- ECM-E000 - Control Module Communication. faulty communication
- ECM-A03B - Communication. Central Electronic Module. faulty Signal
- ECM-250A - Long-Term Fuel Trim
- ECM-903F - Electronic Throttle Module (ETM). Internal fault
- ECM-620A - Idling speed
- ECM-980F - Manifold Absolute pressure (MAP) sensor. Faulty Signal

I wonder whether it is an ETM problem, or is it a wider electrical issue - since two of the ignition coils failed, what would cause them to fail?
Where should I start? Thanks

The coils fail for two reasons: worn spark plugs or overheated top engine. We use only the spark plugs with three prongs on the n/a engine. As for top engine overheating, it will not show on the temp gauge, but it can definitely get very hot up there - much hotter than a normal engine bay temperature. Not easy to diagnose, make first sure you bypass the intake air thermostat (look up on Youtube). Other reasons could be a coolant flow restriction near the engine head.

The stalling to a stop is pretty common, look for any cracks in large the rubber intake hose.

Make sure you have good alternator voltage (14.5v at start, 13.5v after 15-20 min drive), inspect all wires at the alternator, starter, behind the engine bay fuse box, ground behind the left top of the engine

Also inspect the small ECM cooling fan (Yt as well). May also remove the ECM and TCM modules and look underneath for corrosion or humidity at the connectors (needs removing tool)

Long term fuel trim may be the front oxygen sensor if it's the original one

Map sensor is under the front trans member, near the hood lock, may remove it and power it with a 9v batt, and blow/suck through the hole - one way blocked, other way flow.

'Siren' noise inspect the PCV (may also be the alternator regulator)

Thanks for detail reply oragex
I have replaced the spark plugs not so long ago when the rough rpms and misfire started happening. It helped with misfire but did not cure it, and coils failed on new plugs. Plugs are quite cheap Denso K20TT (single prong), previously had the same plugs for approx 20K. I noticed that the old plugs were a bit too white, so it must have run lean (car is on lpg since 100k). I wonder if running lean has raised the temp of the head a bit too much, and now with the fuel trim issue could be even worse, this might have killed the coils?
Should I also get some better plugs, what do you fit in yours?

I have the hose OFF, looks OK as does all the other air/vacuum lines. i cleane dthe throttle flap, but no change. Also the car sometimes runs quite normal (espacially on cold - so it seems electrical rather than a leakage which I presume will be giving symptoms all the time) I am starting to expect a fault Throttle position sensor or something on that unit as the cause of the rough idle and stalling. It sometimes also hangs on 1.5k rpm or higher.

Voltage seems OK, around 14.05 - 14.20v at start, 13.3-13.8v when warm. Ground and wires looks OK.

Will need to try do that.

The readings of the oxygen sensors looks to be OK.

Will need to try do that.

I am also suspecting alternator bearing, I have fitted a second hand one at about 120k. It is definetly not a power steering pump or anything at the cambelt end as this was all done after the noise started.

So I am thinking to do as the doctors do 'Lets try this drug, if it helps it means it was the desease we suspected, if not we will try another one'. So I think will change the alternator and TPS sensor , these seem easy enough for me too do, and we will see if it helps :regular_smile: