stevo1970

iTrader: (1)

My MY00 UK Turbo has started to run poorly, it seems to have started suddenly but maybe it has just deteriorated to the point where I now notice it. Its quite a subtle problem and quite difficult to explain, anyway here goes.

When running off boost it is quite lumpy and when in slow moving traffic jams, when i'm constantly on and off the throttle, it is jerky to the point where my wife has critisised my lack of smoothness. Another symptom is that when it does come onto boost it appears to be in stages, not a smooth spool of the turbo, there are 3 distinct stages as the power increases up to what appears to be normal power. One final thing, it sound a little louder!

My good lady wife thinks this is all psychosomatic, but there is obviously something is on it way out.

For information the car is a Classic MY00 PPP therefore has standard airfilter in the airbox.

Can anyone help?

BBB3

iTrader: (7)

go get it plugged in, maybe a air flow meter

midnight

iTrader: (10)

Have you tried plugging the 2 x black connectors under the steering column to see if it throws up a check engine light code,it might show nothing ,but is a good place to start.

Splitpin

The other guys are certainly correct in suggesting that the airflow meter is the first thing to check and rule in/out. As Midnight suggests, unfortunately most mass airflow sensor failures do not cause the check engine light to illuminate.

There are a couple of things you could check physically. The first would be to pop the bonnet and make sure that all the jubilee clips connecting the MAF tube to the flexi pipe, the flexi pipe to the intake tube, and the intake tube to the turbo are all tight. Also check (as far as you can) that there's no physical damage to any of the above. The intake tube (the one running under the inlet manifold to the turbo) can cause these sorts of symptoms if it splits, although its location makes it the most difficult to check.

Also make sure that the carbon canister purge pipe hasn't become disconnected from the flexi tube.

While you're there, examine the Mass Airflow Sensor itself and check for a stripe of green paint (and white text) on its mounting flange, like this:



If you don't see that paint/text, your sensor is a good six+ years old and is a candidate for immediate elective replacement.

Finally, if the engine is obviously misbehaving at traffic jam/parking speeds, one way you can (indirectly) test the health of the airflow sensor is as follows: Stop the engine, disconnect the sensor (i.e. unplug the grey connector from the sensor under the bonnet), and restart the engine. You will see the Check Engine light on - that is to be expected. Drive around at parking/traffic jam speeds and see if the engine misbehaves noticeably less. If it is more consistent, then you have likely found the culprit. Stop the engine, reconnect the sensor and stay off boost completely until you have the new one fitted.

If that test doesn't demonstrate an obvious difference in behaviour, and if your sensor does have the green stripe, it's up to you whether you want to take your car to a dealer/specialist and have it diagnosed, or whether you buy a new sensor speculatively and see if it improves matters.

If you decide you do need a new one, the part number is 22794AA010, just over £100 from a Subaru main dealer, just less than a ton from somewhere like Import Car Parts or AS Performance. If you do fit a new one, reset your ECU immediately afterwards.

Oh - and if anyone pops up on this thread later telling you about a "test" that involves disconnecting the sensor with the engine running and seeing whether or not it stalls, ignore them. That "test" is meaningless and proves nothing, one way or t'other.

Marin

iTrader: (1)

Could be first signs of knock sensor failure? Sounds similar to what mine did although it threw a CEL after a while. Might be worth getting it checked though.

Splitpin

Not at all likely. There's no obvious mechanism by which a failing knock sensor will cause this type of symptom.

stevo1970

iTrader: (1)

Right an update.

I followed the advice above. Firstly I checked for fault codes, nothing. I then removed the intercooler and checked all the pipe work with no obvious problems, although it was difficult to check the pipe under the inlet manifold. Then with the MAF unplugged the car drove a little worse, it did the same sort of things only more so. After this I reset the ECU with the MAF reconnected, at first it seemed smoother but quickly degenerated to how it was. I took the decision to order a new MAF which I collect Saturday.

Thanks for the advice.

One last thing the MAF was last changed in Aug 08 so has only lasted 2 years, has this been seen before with a standard air filter and only 10K mikes covered?

Splitpin

When you drove it with the sensor disconnected, was it, as I suggested above, first gear parking/jam speeds or are we talking a little more than that?

The reason I suggested that procedure is because, with the sensor unplugged, the ECU has no choice but to replace the absent MAF signal input with an emergency substitute that is looked up from a table on the basis of throttle position and engine speed. While this looked-up value is not particularly accurate, it will usually be much more consistent than the fluctuating, wildly inaccurate values typically output by a badly degraded sensor. So, if your sensor's on its last legs, the engine will usually run more consistently, at least in limp-home mode, without it. Although it's, at best, an indication, rather than something designed to give a 100% yes/no answer.

The fact that unplugging the MAF didn't seem to make a huge difference to your symptoms initially suggests the problem is somewhere else, although these sensors can fail in different ways. It's certainly worth trying a new one - fingers crossed this does the trick. If you fit the new sensor and there's no difference, put the old one back in, stick the fresh one back in the box and leave it on your shelf until the next time you think you need it.

If it does turn out it's gone, it's a green stripe type, and you have a good OE spec filter, then you've been a little unlucky to only get a couple of years of good use of it, but equally, there will be a few that go quicker than that.

stevo1970

iTrader: (1)

Update:

New MAF fitted slight improvement. Any other ideas? Is it worth taking the car to a specialist?

Splitpin

Did you reset the ECU after fitting the new sensor? If not, do so. As above, the fact that running the engine with the sensor unplugged didn't make an obvious difference always suggested that there was more than just the airflow meter at fault.

If you can't (or don't have time to) isolate the problem then putting it in front of a good specialist would certainly be a good way forward.

The one thing I don't see earlier up the thread is any reference to checking/cleaning the idle speed control valve. Certainly worth having a look at this prior to visiting a specialist as it's quick and easy to do. Unplug and two screws to remove the ISCV - then have a look see how much tarry oily crud there is on its plunger - and in the socket in the manifold where it sits. If it's really gunked up, use brake cleaner or WD40 and clean both the plunger itself as well as the mating section of the manifold (as best you can). See what that does.

Oh -as an aside, would you be able to tell me what the batch code is on your new MAF sensor? I'm referring to the four (maybe 5) digit code printed on the mounting flangs, not the longer C36....etc one.

stevo1970

iTrader: (1)

I did reset the ECU, all seemed well for the first couple of minutes but the car then deteriorated to the fault condition.

I'll look out the number tonight.

Can you point me in the direction of the idle speed control valve please.

Thanks for your continued help

Splitpin

ISCV is the metal cylinder about an inch and a bit in diameter, and an inch and a bit long, running across the very top of the throttle body, probably with a black text on white background Unisia JECS part number sticker on it. As above two screws and a connector to remove.

stevo1970

iTrader: (1)

I took the ICVS to bits this evening and gave it a good clean with brake cleaner. There was a black sludge it there but not that much, is the plastic end part meant to seal against a surface inside the aluminium body. is the ICV meant to be closed on anything but idle and therefore if ther seal surfaces were dirty preventing that seal would the resulting passing of air cause my symptoms?

When I first put it back together it was all over the place continuously reving up and down. Took it off again and pulled the plunger out, I thought it broke as the threaded piece came out of the body. pushed it back it and tried it back on the car and the idle returned to normal.

Went out for a test and it seemed better, my test of driving down a hill in second and off the throttle which had produced a bit of shunt had stopped. Will try it again tomorrow night.