teambpl67

Hi all, I'd appreciate a bit of help with my jdm forester s/tb 1998 model auto mods limited to k+n filter and exhaust.

I've been having a bit of an ongoing problem with rough idling/hunting at low revs, searching around on here, the maf sensor mainly gets the blame for this and am I right in thinking the easiest test is to unplug it while the engine is running and it should stop, which mine didn't, although it did stop when I plugged it back in . Is this a definitive test for the maf and so, is mine goosed?

Another problem which has only recently started, is when starting from cold in the morning it starts perfectly but after setting off and usually when I shut off for the first junction the idle speed drops very low and if I don't catch it it will die and then is very difficult to restart, if at all but if left five minutes it will restart quite easily and then run perfectly all day.

I had the battery tested today and it needs one but the place didn't have the correct one, so I will sort that tomorrow, could that be the cause of some problems or should I be looking elsewhere?

Many thanks any advice appreciated

Deano_P1

From what you have described if definately sounds like the MAF is at fault

teambpl67

Cheers mate, I'm thinking the same but wanted a second opinion before splashing the cash, so, does the unplugging trick prove it beyond doubt? or is there a better test?

teambpl67

ok, new battery fitted, and as I expected no difference. It cut out this morning from cold despite trying to keep it revving, it just seems to lose all power, then two minutes later will restart and run fine I thought possibly coolant temp sensor or idle control valve, is there any way to test them? Or am I just going to have to start replacing parts starting with the maf?

Forgot to mention I also have a blackjax anti hijack system fitted could this be causing any probs

Cheers, Bri

Deano_P1

Not sure about the blackjax system but i would start by replacing the MAF.

If the car did not stall when you unplugged the MAF then i think theres a very good chance that this is your problem

olliecampbell

iTrader: (3)

And for £77 its a lot cheaper than an engine rebuild!

teambpl67

ok update, I replaced the maf and it has improved matters and cured some problems but the cold starting problem remains!

same as before, if I let it warm up at idle it's fine but if I set straight off it always dies.

Any thoughts on this?

could some sort of vacuum leak cause a problem like this? I have checked and couldn't see/hear anything but if it's a likely cause I will be more thorough. I was wondering about leaks on the intake side anyway as my car only boosts to 9psi is this low or about right?

cheers guys

Bri

olliecampbell

iTrader: (3)

Hmm vacuum leak, idle control valve maybe. Have you done an ECU reset after replacing the MAF?

Maybe do that and watch it for any error codes which might help you.....

teambpl67

Hi, yes I did a reset and have checked for codes since the maf, none showing, I'm thinking a strip down of the inlet side of things may be in order.

Don't know if it means anything but it has a misfire when cruising on the motorway too just an occasional one at about 3000 but pulls great when I floor it.

Is there a way to test the idle control valve? I did have a look at it previously and it seemed fine

Bri

PeeVee

iTrader: (1)

It would be unusual for an idle speed motor on these cars to go wrong.

It's more likely that you have got a coolant temp sensor fault, as this would give the symptoms you have & they are more prone to failing.

Phil

teambpl67

Thanks for the replies

Phil, I had suspected the coolant temp sensor and have got myself one but haven't managed to locate the little bugger. Am I right thinking it's under the inlet manifold? I looked today from the rear with intercooler removed andfrom the front with alternator moved can anyone point me in the right direction?

Whilst delving in the engine bay I noticed a broken pipe coming off the big pipe going from maf to turbo, it's at the turbo end about 15mm coming off on a 90 degree bend, I'm assuming this won't help matters but can anyone tell me exactly what it is/does?

chris-RB5

First off the coolant temp sensor is located under the altenator IIRC (on classic impreza's) don't know if it will be the same on yours.

And i would say any pipe that is connected to your turbo inlet pipe are only breathers but could certainly cause a air leak thus effecting your fuel/air ratio and causing the lumpyness also have you checked your inlet pipe on the turbo because they generally wear through where the jubilee clip clamps onto the turbo.

teambpl67

Update, thanks for all replies so far but unfortunately it's no better in fact it's worse.

I've changed the coolant temp sensor, no change and I've checked for any leaks on the intake side and found nothing.

The cutting out from cold problem remains and now it sometimes dies during running for example if I boot it then pull up at some traffic lights it generally dies but always restarts quite easily????

Any thoughts on this would be greatly appreciated as it is driving me nuts

Cheers, Bri

olliecampbell

iTrader: (3)

That sounds like a MAF issues, but youve changed it. Does the car (from starting) idle ok?

teambpl67

When I start the car from cold I've started leaving it to warm for a few minutes before setting off that way it doesn't cut out although the idle does fall whilst I do this it never stops though unless I rev it or set off????

teambpl67

Quick bump

also I have to mention that the maf I put on was second hand although I heard the car running and it was perfect!

What about the lambda? I did a test as found on sn and the results seemed right but could it still be causing a problem?

olliecampbell

iTrader: (3)

Hmm coming to the end of my ideas here....

I'd be thinking (with my basic knowledge) spark plugs, HT wires, coil packs (the electrics of getting the engine ticking over). Then induction...so air leak, idle control/boost control or MAF...and then I'd scratch my head and call someone like Roger Clark Motorsport or API etc etc

MazingerZ

teambpl67

Have you found the problem mate?

I am having the same issue with my v3 STi, only that mine does not stall but the revs go just below the 500rpm line hunting before stabilising at the normal 800 odd RPM. also occationally I get the CEL only when doing 40mph in 4th, it disappears as soon as I dip the clutch as I brake for a junction.

I just changed the MAF (2nd hand, orange label); although I believe the ecu has not been reset properly; I unplugged the battery and going to leave it like that for 1 hour or so.

has anyone got any ideas?

cheers

olliecampbell

iTrader: (3)

That sounds like a MAF issue too...try connecting (under the steering wheel cowling) the green and black connectors. Start the engine and drive for a little bit (usually about 100metres). Your CEL will come on and after the little drive will start flashing at you...its flashing the codes for errors at you.
Note them down and then do a search on here for error codes.

teambpl67

I'v had no change with the running of mine, if I boot it then stop at a junction it's almost guaranteed to cut out, no cel but I have just checked the codes and it's given me the maf code. I'm gonna clear that and see if it gives it again then I guess I'll have to bite the bullet and buy a new one I'll post what happens.

teambpl67

Update, I had a few days off work so decided to investigate and lo and behold the turbo inlet pipe is split as mentioned above

I'm now trying to source one. So does anyone have an idea of the best place to go in south yorks area?

All the impreza breakers I call are saying they don't have one to fit the forester but I'm fairly sure they're the same but need to see what I'm buying to make sure,

Cheers

Shark Man

Let that be noted by people who read thread sand think all running faults are MAF related - it was MAF related, but the the MAF reading error was caused by an air leak, not a faulty sensor. The sensor will not function correctly if such a fault exists, and will "seem" faulty when it isn't.


Happens a lot on many cars. One reason why I say the fabled "unplug test" means absolutely nothing in regards to the sensor's condition.


Something to bear in mind when taking advice on here, when iffy "tests" get spread across the interent ...Best one I've seen is someone doing an "unplug the MAF test" then reading the ECU fault codes...and finding a MAF error code logged. No s**t! Its just been unplugged!!

olliecampbell

iTrader: (3)

Not doubting you at all, but I would have thought checking the ECU error codes would have interrogated the MAF whilst the car is idling, and therefore the split not causing much of an issue.....

I could be , and am usually, wrong!

Shark Man

Your right in some repects in relation to current logged faults, but faults logged during normal driving will still be held in memory.

Checking error codes is a two step process; previous (not current) faults stored in memory from driving - as long as they repeatedly occur within 6 or so engine start/stop cycles (possibly more or less - can't remember the exact number on Subarus), otherwise it self clears.

Then there is current faults - which show what is present at that actual point in time. So if it was read with ignition on, then only faults from that point will be shown as current, if the engine is at idle, only faults most notable at idle will show. So yes, small faults may not show as current fault when at idle....but the car can be driven to see if any codes crop up whilst driving - on the fly, so to speak.

Obviously, the latter isn't done very often, but it is possible to do. The reason why its not done often, is the usual practice is to the reset the ECU and clear all logged faults, then drive the car for a period, and check for any new codes that are logged in memory - This rules out ambiguous fault codes that were previously logged which no longer show in the memory, and confirms ones that reoccur.

Unfortunately, with regards to airflow sensor output checking, the ECU on the early cars is not that clever, it can only check the airflow sensor based on tolerance limits for its given voltage output, it doesn't use feedback from other sensors to give hueristic testing of the airflow sensor's accuracy. So has difficulty knowing if the reading it gives is correct or not. Unless its totally out of its tolerance limits (say, open circuit - disconnected, or short circuit or a major induction leak). So yes, more minor leaks don't always give any fault code, but can still affect the engine running, as the sensor's ouput is inaccurate.

Later cars are better, but an air leak can show a MAF or fuel trim limit error, based on feedback from the oxygen sensor. Although on some cars it can log an oxygen sensor error instead - another red herring. And still, only codes occur if those tolerance limits are exceeded.

olliecampbell

iTrader: (3)

Some good info thanks!

teambpl67

OK update.

It's not good, I was convinced the replacement of this pipe would cure all evils regarding problems stated above, however all problems are still present I think the idle may be slightly better but that may be the placebo effect, I don't know.

I've checked codes, nothing showing, I'm at a loss now. Only thing I did notice was the turbo shaft did have a little end float which although I know requires attention wouldn't cause the running problems I'm experiencing, or would it? Any thoughts appreciated.

teambpl67

Bumpitty

daves2rs

You tried the crankshaft sensor? It might not a log fault even although its fubar. Idle, fuel all controlled by this. See if a mate has one to try out.

teambpl67

Ok things have gone from bad to worse.

As I was driving home (on christmas day of all days) there was a distinct jolt as something happened.
The car started running poorly with a lack of power and I ended up running with boost just about all way home just to keep going even on flat sections. I didn't stop because I feared if I did I would be stranded so just pressed on and hoped for the best.

40 miles later as I pulled up at home it died

Now it will start but has a constant misfire on no. 4 ? cylinder. ( nearside rear )

No check engine light or fault code I'm thinking head gasket or piston damage would any body agree?

I haven't been able to do a compression test as I haven't got a suitable tester. No other signs of head gasket failure although it has used a little water

all thoughts appreciated

teambpl67

Ok, I did a crude compression test and it was obvious no.4 had a lot less compression so I have stripped it.....and found....a burnt out valve.

I'm quite pleased as I was imagining allsorts, so the next question is, does anybody want to sell me an exhaust valve?

The dimensions of the valve I have are.

shaft dia. 6mm
head diameter approx 32mm
length approx 115mm
1 collet groove approx 5 mm from valve tip