cefski

This is a long one, so please bear with me...

Strange and potentially expensive things are happening to my UK 00MY Imp Turbo, which I've owned for over 2 years. ECU is standard and un-modded, Scoobysport/Janspeed decat downpipe and backbox, standard catted centre section, STi panel filter.

It started like this...

A few weeks ago, the car failed its MOT because of emissions, so I swapped the decat downpipe for the catted oem one. Failed again on re-test and found that the problem was most likely with the lambda. This was replaced with a used but full working order jobbie, and the ecu was re-set using the green and black plugs below the steering column. The CEL blinked steadily and constantly, indicating that all was well. THe car passed emissions with no problems.

However, I found that the car was a little hesitant at just below 3k rpm once the catted pipe was fitted, both before and after the O2 sensor was replaced. The hesitancy I mean is described to the tee in THIS THREAD, but I'd not experienced it before, and fully expected it to disappear once the decat was back in place.

No such luck. It's still there and is most noticeable when the car is cold, but like I said, this didn't happen before the MOT and the pipe/O2 sensor change.

Yet more strangeness today when I had to replace the battery. It was disconnected for about 10 minutes whilst the old one was removed and the new one put in, probably not long enough for the ECU to be re-set, I thought. So with the new battery in, I started the car and let it idle whilst I paid the bill (though I did blip the throttle to hear the exhaust note echo around the garage ). The engine started hunting noticeably and constantly, from 800rpm, down to about 4 or 500, then back again, time after time.

Drove away from the garage and the car felt fine during the 5-mile drive home. Once I'd parked up outside the house, the hunting started again. Revved it to about 3k rpm and let the throttle go. Needle dropped straight down to 800rpm, with none of the usual slowing at 1k rpm. It then started hunting again. I cracked the bonnet and disconnected the MAF. The engine ran on as if nothing had happened and only stalled when I re-connected the MAF.

Did a proper ecu re-set this evening. CEL showed no faults, but the car is still hunting, though it's less pronounced - the rev counter needle hardly moves.

Do I trust Japanese wizardry and do nothing, or trust my instincts and change the MAF?

If the MAF is going/has gone, how safe is it to drive the car before I get it changed?

Cheers

Kev

SuperFlyGuy

Your symptoms, especially with the ECU reset (as the ecu learns to overcome problems such as failing MAF and Lambda sensors) do appear to be MAF, hence once ECU is reset it defaults back to factory settings and so the problems appear.

I thought that on a normal car if you disconnect the maf it stalls or behaves irratically on idle. In your case nothing happens hence MAF problem.

I would advise you do not drive car at all as MAF failure has been linked to engine failure at high revs and max boost due to poor fueling.

Good luck

cefski

So off boost, it should be ok???

Peanuts

iTrader: (15)

stand back from the car, go to subaru and hand over the £75, replace the maf and then you should be ok to drive again.

seriously, is it worth the risk of letting a small cheap consumable part destroy your cars powerplant

cefski

Good point well made

kev

Dark Blue Mark

See here:http://bbs.scoobynet.co.uk/showthread.php?t=394381

Ive had a couple fail MOT on MAF, and they very rarely appear as a CEL fault. Drive off boost for now, but its not really right to say dont drive it at all. Just get it replaced ASAP.

MB

David MY99

You can try to clean the idle speed valve first. If that doesn't help it's most likely the maf as mentioned before

Bob Rawle

Sounds to me as though its just the closed loop fueling adding and subtracting fuel as it works, the new lambda sensor will be allowing the ecu to run the car leaner, the ecu rerset will have discarded all the old fuel learning that was keeping it running reasonably but rich with a failing sensor fitted.

If you give it time it may learn back however as a test unplug the lambda connector and see if it changes the behaviour, probably will. If so see above.

bob

cefski

Cheers for all your help, chaps.

New MAF sensor ordered (£77 inc vat) as a precaution. Still having problems with hunting at idle, though the engine will now stall if the MAF sensor is disdonnected. We'll see what difference the new MAF makes.

Hmmm... Bob Rawle... the mere mention of that name has me trying to work out a way of persuading the missus that a re-map is absolutely essential and well worth the money...

Kev

Peanuts

iTrader: (15)

LOL
it helps if you do a "wife-pound" conversion...
currently the exchange rate is very good with £250 wife pounds actually getting you the full cost of a Bob Rawle remap
its the way to go