TomCOYS

Stalling/Rough Idle - Many things checked - No clue

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Hi All. 

 

I have a 4th Gen Subaru Legacy EJ204 (twin cam/AVCS on the inlet valves), that will not idle smoothly and will engine stall.  If you pulse the throttle and bring the revs up it will start and anything over 2kRPM the engine will behave but under that range the engine will quickly stall.  Other than that the engine behaves when driving.

 

I have checked so far/this is what I know so far - 

1.  Timing belt.  The timing belt had been done by the previous owner by a mechanic. I think less than a year ago.  The belt had slipped one tooth when I looked at it last weekend.  Took belt off put back on. Checked operation.  Belt is good - problem remains.

2.  Spark plugs have carbon deposits on them.  The previous owner had them changed when this problem started.  They look like the expensive spark plugs.  I checked them for operation by grounding them and turning engine over.  They spark OK.  Will change them regardless next weekend.  At same time checked the Ignition coils they are working as well.

3.  It looks like a new MAF Sensor.  Have swapped with another MAF and it made no difference to the problem so it looks like the MAF is OK.

4.  Checked the throttle body.  Gave it a clean and tested operation.  Looks good.  I am confused though because it appears to not have any kind of sensors on it?  No Map/No IACV?  How is the engine managing idle control?

5.  Checked for vacuum leaks with brake clean spray.  None found.

6.  At times the engine back fires and fuel is getting down the exhaust.  It also misfires at times when you are over 2kRPM.

7. I put a cheap knock off engine code reader to it.  No codes found/no check engine light.  However, when I took all the above sensors etc out last weekend a check engine light has appeared.  I can't check it till I find a way of getting a correct code reader.  I tried using the key on>headlights on>trip computer stick technique but it wouldn't work.  So now I have an check engine light.

8.  Checked engine compression.  This is what I got

Driver side Closest to radiator - 200 PSI

Driver side Closest to bulkhead - 210 PSI

Passenger Side Closest to radiator - 200 PSI

Passenger Side Closest to bulkhead - 210

I have searched and searched but can figure out if too high compression?  I figure that it can't be head gasket or a low compression problem.

 

Anyone have any ideas on what to do next?  I have done some digging around, could it be the AVCS playing up?  Might be fuel injectors? (but engine runs fine at higher RPM and speed).  Might be one of the o2 Sensors?  If it is AVCS looks like you can change a sensor or actuator to fix it?  Getting any kind of information or solutions on the EJ204 is a nightmare.

 

Cheers everyone, thanks in advance.

 

Tom.

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For your leak check did you just spray brake clean around lines to see if any change in engine note was noticed? 
A proper low pressure test/smoke test is the better way to ensure none of the intake pipes are damaged along with any hard to reach lines you may have missed. 

 

There is no dedicated IACV on these cars as they use an e-throttle so the ECU just opens the main throttle body to maintain idle. There should be a map sensor on top of the throttle body though. Wonder if the last owner has replaced the throttle body with one from a GT which doesn't have one on the body itself. Any loose wires/plugs floating around in that area?

 

A slightly leaky injector could cause it to idle wrong but be fine as rpm's and injector duty rises. 

 

I proper code reader/logger is a good purchase as testing for a lot of faults like AVCS ones on these cars really needs to be done by viewing the data and then moving things around.

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Posted (edited)

Thanks for the reply.  

1.  For leak check sprayed and checked for change in engine note.  Not a proper smoke test.

 

2.  There is no loose wires/plugs around the throttle body that I could see, but will have another look.  I think you are saying that I should have the throttle body with the MAP sensor on it rather than the one I have which does not.  The GT model is turbo?  Mine is NA. The ECU would still be able to run engine even if missing the MAP sensor?

 

3.  Yes. Check injectors is next step I think.  

 

4.  Just read a pinned post about oil getting into ECU from AVCS sensor wiring, I should check for that as well?  

 

Was trying to avoid the Subaru dealership but might have to get the proper code reader.

 

Cheers man.

 

Edited by TomCOYS

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Throttle should in theory look like this with the map sensor sitting on top unless certain year's did things differently. Yea in thinking maybe a turbo one. For a NA it doesn't matter as much if it is unplugged as it will resort to a certain figure which could be some of the problem as it might be correct when revved but quite wrong when idling. This is where being able to see the operating data would really help a bunch.

 

49326808777_4de1d21b55_b.jpg

 

49326590071_28a0595a8c_b.jpg

 

What part of the country are you in?

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Thanks for reply.  Stuck in Queenstown but would travel for help :)

 

Problem being I can't remember seeing an extra wiring or connectors when checking all that stuff the other weekend so I think the car might be one without a MAP sensor on top like I have currently.

 

 

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When I first got the car the battery was flat so took it out to charge overnight, so ECU got reset then.  Made no difference.

 

When I swapped the MAF I didn't take the connectors of the battery so no ECU reset.  You think it is worth reset the ECU by battery disconnect and then trying a different (known working MAF) in there?

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Pull the AVCS solenoids out and check for debris from the banjo filters collapsing.  Ensure that the solenoids can move and put them back in.

 

Very common issue causing rough idle/low rpm running.  Pulled mine out and the filters were stuck in the solenoid mechanism jamming it at high advance.

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o2 sensor? I had this issue recently. car was over fueling anything under 20% throttle due to fault with o2 would pop and bang with normal driving occasionally and would have rough idle and nearly stall. 

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Yes, Thanks for all the replies.

This weekend (if I can get into the workshop) going to test the up/down o2 sensor and have a look at the AVCS.

 

From what I can gather on the AVCS, there is a banjo bolt, two gaskets, and a filter that could be causing the rough idle. 

 

Going to change engine oil and filter just in case as well.  

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Just to follow up.

 

Got car in workshop.  It was the AVCS filters.  The filters on both sides had come apart (below the Banjo bolt).  Meaning the solenoid couldn't push the valve up and down correctly.  Both valves were stuck in one place because there was tiny bits of plastic stuck between the housing and outside of the valve.  I took the solenoid out cleaned it thoroughly.  More broken bits of filter came out.  Tested the solenoid.  Put it all back together and boom.  Car working!!!

 

So now I need to put in new filters and washers and an oil change and good for another 10000km.  Thanks for all the help guys.

 

Still have engine light but I'm leaving the battery off for a while hopefully the ECU will forget!

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