Hawkeye D

Hi all,

Gutted as I seem to have an issue which hopefully isn't serious.....he says.

2007 STi Spec D 85k miles. On a cold start up, most of the time the car is now spluttering a bit, like it's misfiring almost. It will struggle to get over say 450 rpm and it hunts a bit, and after 5 seconds or so it will go up to the normal cold idle speed of approx 1200 - 1300 rpm.
I appreciate that we are now in the winter months, but something isn't right. We've had colder snaps by far and the car has been fine.
It's happened about 10 times now, a few times a few days ago it was totally normal. It also happens on a hot start, but no way as noticeable.

Other than that, the car seems fine. No massive fuel consumption, no CEL....everything seems ok. It's a fully forged 35k miles ago engine. Spark plugs changed 25k miles ago.
I'm not seeing any smoke of any colour at any stage of idling / driving / boosting.

It's a fly by wire car, so maybe the throttle body control?
Try cleaning the MAF or boost control solenoid?

Any suggestions?


Many thanks :-)

Vxr2010

are you using the throttle to start it if you are don’t , try an ecu reset , disconnect battery pump brake pedal about 30 times , leave for 10 minutes then reconnect battery , i had to do it on the mrs car as throttle was being used to start it plus it’s like doing a hard reset on an iphone

Hawkeye D

No never used the throttle on start up ever.

I can try an ECU reset via my PSi3 data monitor.....

Vxr2010

i would try a reset , if that does not work , when you start the car prime the fuel pump two or three times just to see it’s not a fuel pressure issue , it’s difficult to diagnose issues i can only go on what things have gone wrong for me in the past

Chrisp11981

iTrader: (1)

It might be worth checking your idle air control (IAC), sometimes they get gunked up with carbon and cause issues similar to what you've described.

If you take it off you need a new gasket (about £8 from Subaru), and iirc it's 2 torx screws to get it off.

Once off check it's free to move, it's like a roller arrangement and should be relatively easy to move and be a smooth motion.

If it's stiff to move (grinding), then clean out and refit. I found I had to move it round a bit at a time and use brake cleaner and a cotton bud to wipe the carbon away. Once it's clean it should return to its resting position.

Hope above makes sense and helps.

Cheers,

Chris.

Hawkeye D

ECU reset and 3 x priming the fuel hasn't worked.

I've seen IAC's but I can't see that part on my throttle housing.....

I seem to have this set up :

Rather than this :

Vxr2010

is it worse on a cold day or always the same ? coolant temperature sensor making things too rich

Chrisp11981

iTrader: (1)

Ah right sorry, didn't realise they were different. Although my symptoms were similar to what you describe, might be whatever you have fitted that does the same thing (if it exists)?

Cheers,

Chris.

Hawkeye D

Where is the coolant temp sensor?
Is it under the inlet manifold somewhere, on the crossover pipe?

Vxr2010

try searching on here with this , there’s an old old post that may help , i think it’s near the turbo but subaru seem to move it around for some reason

Engine coolant temperature sensor location

Don Clark

Yes. Behind the alternator.

Hawkeye D

Thank you all, but I really think now that it's HG....again.
I've had another significant water push into the overflow bottle into the radiator. I've found it high several times, but the header tank has always been full.

However, last night the header tank was only about half full, this is something I remember very well 4 years ago before rebuild.
I'm wondering if the misfiring is due to a bit of coolant getting into the bores overnight etc.

No overheating, and still got hot air from the heater matrix. But it does gurgle in the mornings....another sign.

Gambit

iTrader: (6)

Half full header tank isn't a good sign but you should have seen overheating to lose that much

I'd the headgaskets go on my car, also forged, at end of last year but I wasnt losing coolant, we'd just notice some temp creep when mapping - this wasnt enough to cause the dash temp gauge to move but temps where up near 106c

Got it checked over and it was early signs of headgasket failure on one head, the other wasnt far behind it.

If you think it is headgasket then get it checked over asap and just stay off boost. Did you notice if the top rad hose is starting to balloon? Was another tell tale sign on mine.

Hope it turns out something not as drastic as headgaskets for you

Vxr2010

i’m hoping it’s not hg , the symptoms i had was pressured header tank looked full , but on start up level dropped to half, plus i had coolant filling up non pressured over flow coolant tank , sometimes the rad cap on the radiator or the expansion tank cap can give issues if not holding the pressure , i have always had hg failure symptoms of above , i have not had coolant leak into a bore , if it was you would get a lot of steam on start up , check your thermostat , check the rad caps , fingers crossed , i assume when they rebuilt yours are head bolts and non subaru hg gaskets used ?

Hawkeye D

My PSi3 data monitor always shows about 85 degrees for CT (coolant temp) and when in traffic the fan operates at 97 degrees and takes it down to about 84 / 85 again. Reliable there.

The build was ACL bearings, Manley rods, Mahle pistons, Cosworth HG's and ARP head studs (I think 11mm rather than 14mm) and running a 1.3bar header tank cap for 6 months now. I put that on to try and slow the water pushing symptoms. It's a legit cap genuine STi one from ICP, and not a cheap Chinese knock off...I've seen what they look like.

The top hose does get pretty firm but doesn't balloon no. Thermostat is only a few years old.
So I'm stumped really....no push of water today I will add.

However, there are bubbles that enter the overflow tank by the radiator...but AFTER I switch the engine off. After a boost and engine still on....no bubbles.
Heating working, but as said gurgle on start up from the heater matrix. Plus this evening after work it did stutter again on cold start up....

With no CEL, how can they test a possible bad CT sensor? Having said that, the PSi3 CT readings are all totally normal, so perhaps it's not a faulty CT sensor..

Vxr2010

the gurgling is not unusual , the bubbles a few is fine , as long as it’s not all the time then it’s fine , the heater matrix blowing cold can be a possible but both mine do it randomly so it can be other things but not necessarily an issue , head studs good idea , are you running a lot of boost as i would not expect issues after a fairly recent rebuild

Gambit

iTrader: (6)

Getting a higher pressure header tank cap is just moving the issue elsewhere. If it was on a std cap I'd have replaced like for like, if it was still spewing then you have an issue else where. The header cap is designed to be a lower pressure than the radiator cap to help it flow into radiator but you've 1.3bar on both header tank and rad cap

I'd put a new genuine 1.1bar back on it first off

Hawkeye D

The boost is nothing special, about 1.5 bar.
I will try my old cap, it wasn't faulty so will put that back on this morning and see what happens - standard 1.1 bar header tank cap. The radiator cap is already standard and is only 2 years old. No leaks anywhere that I can see. Will check floor carpets and hope they are dry - in case the matrix has a leak, but plenty of hot air as said.

I wonder what the bubbles are after switching it off? When HG went before the rebuild, there was bubbles constantly whilst engine on which made sense.

Gambit

iTrader: (6)

if you have a PSI3 gauge then set it to coolant temp gauge and give the car a decent run and load it up on 5th - watch the PSI3 temperature gauge if it goes higher than 105 id say you have an issue. iirc itll record the max temp anyhow

Hawkeye D

No difference in coolant temp to normal readings on PSi3.
Without a CEL it's really frustrating...could be hardware.

Tonight it stuttered again pretty bad....sounds almost like oil not getting to something...rattly and wobbly and misfiring.
The oil pressure light goes out quickly as normal....but wonder if I have a sticking bucket? But surely then I'd get a CEL?

Could possibly be a coil pack breaking down, or even a loose or duff spark plug. But again..a CEL would be nice.
I'll do a video tomorrow morning and YouTube it....I think you'll all be quite horrified at what you see and hear.....
Whatever this issue is, it literally started overnight...

Always used Millers CFS 10w 60 since rebuild, always changed every 4k miles, topped up here and there when needed but never much or any needed.

What worries me is also a chance of water pump or oil pump bearings breaking down and snagging on the cambelt at start up?
Oil pump....hmm I wonder.
I'm clutching at straws with it at the moment.

ossett2k2

iTrader: (9)

Always thought 10w60 a bit thick for a road car?
can't think that would cause issues tho.
maybe a sticky avcs solenoid?

lockheed

iTrader: (1)

I had a strange happening awhile back with thick oil .

What happened was that it had managed to push the thimble filters for the avcs down too far and the engine started making some ticking noises , that was with motul 300v 15w50 so I removed the thimble filters with no ill effect I also changed to motul 300v 10w40 .
it doesn't sound like your problem tho.

Hawkeye D

Agreed, I can't outrule that, and did have that before on the drivers side bank a few years ago.

I had no symptoms as described in the thread, and a CEL I assume straight as the fault started....

Gambit

iTrader: (6)

The reason I said to use the psi3 for a coolant temp check is because at 105C you are on the verge of overheating. The dash needle will still show 'at temp' it's only until its proper cooked will the dash needle move.

Nowt wrong with 10w60 except that itll take an age to get to its working temp.

Hawkeye D

Nah sure I get that, the display on the PSi3 gives me live readings...nothing untoward with the coolant temps....
I've always been off boost until a good 10 mins down the road etc.

This is what annoys me...if I ragged my car around I'd expect issues, but I'm actually really sympathetic to it pretty much.
I actually want a CEL lol, and it's unbelievable that with how the engine behaves after startup that I haven't had a CEL / P code.

Nor a historic one as I can check on the PSI3....no P codes current or stored...nothing!

Vxr2010

maf sensor playing up , try cleaning it ? the mafs don’t often fail , is fuel pressure ok ? what area are you in ?

Hawkeye D

MAF was as clean as a whistle, cleaned it anyway with electrical cleaner. I had only cleaned it about a year or so ago.

I tried priming the fuel system 3 times by ignition on and off etc until I could hear the pump stop priming....made no difference.
My fuel pump is about 5 years old...left in from when I had PPP fitted.

Hawkeye D

Ok, so she's toast.

Long wait for oil pressure light to go out....possibly rod knock but hoping just the usual forged piston slap. It doesn't really continue to knock up the rev range.
I apologise for the state of the filming, but enough to get the idea.
I need to get it transported to my specialist, I can't drive it 30+ miles like this.

Start from cold :


Then, an hour later (still cold) the driveway turns into a coolant sauna :


I hope just a serious HG blow, could be a cracked block or sleeve, warped / cracked head... time for open heart surgery, oooh yes! Time to close the deck or at least pin it if so.
Gutted, but at least something has now clearly manifested....
I certainly haven't seen this coolant steam before, funny smell, definately not fuel or oil though.

Luckily have my trusty 1.9 TDi 54 plate Passat on standby to use. AWX is bulletproof, but does need an OSF CV joint....man the joys.
It may even cost me £30 in fuel for work this month!

Vxr2010

well fingers crossed , keep the post updated when you know what the issue is , hopefully not too much £ , back to original engine builder as a failure after not a lot of miles seems strange ?

Gambit

iTrader: (6)

Is there a catch can setup on that car?

It doesn't sound too bad actually. And that 'coolant burn' is just condensation on a damp day. If it was truly coolant you wouldnt be able to see itd be that thick