topshot

iTrader: (4)

Hi,

I have just purchased a W reg Impreza 2000. It starts/runs fine but at idle there is a slight fluctuation, it varies between 100and 500rpm when both cold and hot.

Its done 80k with FSSH, is it worth me replacing the MAF as i have read these can go wrong? anything else i should be checking?

Splitpin

Welcome. First thing to do might be to link up with someone closer to you just to make absolutely certain that the fluctuation you're experiencing is "abnormal".

Second point is to ask whether you're sure you're reading the revcounter correctly. The first mark is at 500rpm, not 0, so the idle speed is probably a little higher than you're thinking at the moment.

Mass airflow sensor would be an obvious candidate for precautionary replacement - although before doing so you could have a look and see if there's a date code marked with white ink on the mounting flange.

While you're there, is an induction kit fitted? If so, and especially if the car hasn't been mapped to suit, your best option would be to chuck it and fit a standard airbox and induction tract - ideally with a good aftermarket panel filter.

Finally, before going any further, look up "black plugs" here or on Scoobypedia. You'll learn how to put the ECU into read memory mode - which will display any stored fault codes via the check engine light. If you get any, let us know.

If you do replace the MAF (part no 22794AA010, about £100 from your Subaru dealer), make sure you reset the ECU afterwards - the procedure for doing so will probably be covered in the same place the read memory mode is documented.

topshot

iTrader: (4)

Hi, thanks for the reply.

The car is running standard airbox and filter. I meant the revs fluctuate between 100rpm and 500rpm from the normal idle position, sometimes it goes up to 1000rpm then back to 800rpm etc. the revs dont hang on gear change.

Ok i will have a look and do a few tests saturday, ill post my findings up.

It's just the MAF horror stories scare me!!!

topshot

iTrader: (4)

Right i have had a full service and new camblet fitted, no fault codes found and it drives fine but its still got a slight idle fluctuation. The garage had a look and cleaned some vacuum pipes and it was ok for a while

It idles at 1500rpm when cold and slowly drops down to the normal idle as it heats up but then sometimes the idle increases by upto 200rpm and then falls back to normal. It doesnt stall or go above 1000rpm at idle and there is no hesitation when accelerating.

ICV has been cleaned so now im stuck, any ideas?

99greenwagon

iTrader: (39)

sounds like plugs or maf sensor,do an ecu check.could also be knock sensor.

99greenwagon

iTrader: (39)

oops sorry,just noticed u did do a check,my maf was knackered but it didnt show on the ecu check,i still say maf or plugs.if u do fit a new maf make sure u reset ecu after fitting it.new maf is good for piece of mind anyway.

topshot

iTrader: (4)

Thanks, plugs have been changed as part of the major service. Looks like a new MAF is next on the list to try then, i can get one tomorrow in the meantime will it be ok to drive (obviously not booting it)?

If new MAF doesnt fix it what should i be checking next, how do i check knock sensor?

sorry for all the questions, im an impreza newbie!

99greenwagon

iTrader: (39)

if the ecu isnt showing any codes then your knock sensor and others are most probably fine,drive it steady in the meantime .dont 4 get to reset ecu after new maf sensor.if no luck then it is probably a vacuum leak of some sort,itercooler and all hoses around this would be a good place to start,but i reckon its probably maf if its never been changed,they are a particularly weak part on the my99-00.i replaced mine and the car drove alot better.the ecu has to be reset after fitting.it wont be a waste of money to replace the maf.

99greenwagon

iTrader: (39)

if all of that fails i would also look at coolant temp sensor.

topshot

iTrader: (4)

Right MAF has been changed and ECU reset. It runs and pulls very well but there is occassionally still a slight dip in the revs at idle nothing more than 100-200rpm and its only for a second before rising to normal idle. I was told today this is normal for the boxer engines is this true? am i worrying about nothing?!

99greenwagon

iTrader: (39)

thats normal mate,i reckon u were well due the new maf,does it only dip slightly when the cutch goes in from mid revs? eg...running in 2nd gear at 3000rpm,foot on the clutch,revs drop to just under 7-800rpm then setlle at approx 700rpm?if so then u have nothing to worry about at all mate.

skinner

It could be your fan cutting in most cars rpm dips for a second due to voltage/amp change.