Harty2000

Hi all
As of yesterday I acquired a MY00 uk turbo.
This morning when i started it the revs stayed slightly high but eventually dropped to around 800 revs.
The next time I started it, it did the same.
As I know the MAFs are quite weak in this model, I unplugged it with engine running and the engine didnt cut out, but dropped revs quite low down and idled quite rough. A few times the engine would cut out aswell.
If the maf has gone would the engine always cut out when the maf has been unplugged or will it just run rough?

Rich D

iTrader: (12)

it's meant to idle high when you start it up from cold, Jap cars do this, it's perfectly normal

Harty2000

Ok cheers, even though it was doing it after around 15-20 mins of driving aswell when started up again or do they take even longer to sufficiently warm up
Just out of interest though, on the maf testing what should happen when it is unplugged with the engine running or when engine started without it plugged in?

Rich D

iTrader: (12)

if you start it when warm, how long does the high idle last for?

after this is it 'normal' even if you rev it a little?

sounds like it could be the idle control valve, try cleaning it


if you unplug the MAF it will idle like a bag of spanners, you can't determine if it's faulty or not by doing this

P600wrx

iTrader: (1)

when cold my wrx runs @1650rpm and over a period of 5-8 mins it slowerly drops

TonyBurns

iTrader: (3)

Thats far too high, you shouldnt really go above 1k before settling down, and it shouldnt take long to settle either.

Tony

Splitpin

No it shouldn't take anywhere near as long as 15-20 minutes to get the coolant temp hot enough for normal idle. For what it's worth, 700-750rpm is the correct hot idle speed on an MY00 UK car - and you would normally expect to see this within eight minutes of a cold start in our current temperatures.

If you're not getting stable idle after 20-odd minutes, there are a number of explanations other than the airflow meter. A faulty coolant temperature sensor is the other obvious one - how far up the temperature gauge does the needle settle after, as above, eight minutes steady driving?

You're not actually testing anything there, and disconnecting the sensor with the engine running can do more harm than good. It doesn't prove anything one way or the other, and can actually damage a good one due to the sudden withdrawal of power to the air flow sensing element with air still passing it.

I presume you did it because you've seen an oft-repeated story on here about that if the car stalls after the sensor is unplugged, the sensor is "good", and if the car doesn't stall, it's "bad". It would be fabulous if that were true as it'd be an easy way to tell the difference between good and broken sensors, but unfortunately, it's complete and utter bullsh*t.

That "test" can easily "pass" a dangerously degraded sensor as good, which is absolutely the last thing you want in this situation.

There's only value in trying this if the car is acting up quite a bit at idle. If you stop the engine, disconnect the sensor, restart and find that idle stability is notably improved, then it's more than likely that the sensor is in need of replacement.

However, this is not an authoritative test. The only way to test the sensor comprehensively is either on a bench airflow test rig, or, in the car, with a datalogger. You can also tell a failing one pretty easily with a wideband AFR meter or knock monitor.

As above though, it's possible that if you do have a problem with your car at the moment, the AFM may or may not be the cause. It also sounds possible, depending on the exact behaviour you're seeing, that there's nothing actually wrong at all.

Harty2000

Spltpin, many thanks for that answer.
I regret doing that test now then, just hope I havn't done any damage to the maf if it was ok in the first place.
Im going to take the car out for a short drive tomorrow and see what the revs and temp are then, and then reply on this thread if you dont mind having a look.
I appreciate your input

richgreenscooby1

iTrader: (2)

why dont you put the connectors together under the dash and read the fault codes , and see if there is any , least its a start.

Harty2000

Had a nice drive in it today, and the revs seem to be spot on now, it idles at around 7-800 now and seems to be steady there.
Temp stays and just under halfway aswell so fingers crossed its all good.
Its just my alarm which has buggered up now :-(