Recently changed the clutch on MY 99 Impreza.
Since clutch change the engine will not idle correctly, tickover varies
between 500 and 1200 revs and constantly hunts (fluctuates).
Idle from cold start is normal (constant) and the car drives with no
problems, there are no reported faults when I do an ECU check & there
appears to be no loss of power.
I guess there is a pipe or lead off somewhere but cannot locate anything
missing or obvious.
Any suggestions of where I should look to sort this out will be gratefully received.

 

could be your maf going! underneath the intake tube connecting the airbox to the intake manifold there is a tube which connects to the canister is that still connected because it might be letting in unfilterd air

 

Definetly sounds like the maf sensor. Mine did exactly the same a couple of weeks ago. Sensor replaced and fine now. Does it almost stall when you leave go of the accelerator?

Chris

 

What you are describing here is exactly what mine is doing!!
Im running a blitz induction kit with mine could this be the cause?
And can it run without the sensor or does this **** the engine up?

 

MAF - Get it checked/changed right away or end up with a destroyed engine.

Whilst you're at it, get your Lambda ckecked/changed for the same reason.

Buy Knock/Lambda Link to keep an eye on these 2 in future



An induction kit will shorten the life of a MAF & you do need it as it measures air coming into the engine, so adjusts fueling to suit the given throttle position. If its fecked (not working or absent) then it could lead to det, which destroys engines - I know

A knackered Lambda causes engine to run too lean, leading to melted pistons etc

Ideally, these items should be changed annually.

 

Engine does almost stall when letting off accelerator, if I unplug MAF then engine idles without any problems - looks like I am heading for a new MAF

 

Yep and me!

Ive been told to put my airbox back on to stop it happening again as well!

More expense

 

This is probably not a bad idea. There are additional risks involved in running an induction kit due to the dangers of vibration accelerating MAF damage, or indeed of the change in airflow characteristics making the sensor misread.

Given that there's little to gain from an induction kit in performance terms, a good quality panel filter is a far better all-round bet.

 

Classic fcuked MAF symptom. Suggest you steer clear of open-loop running until you get it replaced. I think the clutch change was a coincidence. You didn't disconnect the battery, or reset the ECU by any chance...?

 

Sorry to butt in again!!!

Why did you ask if he had reset the ecu? because my troubles started when i changed my ecu for a z4.

Can this mess it up as well?

 

Ohhhhhh yeah. The resetting of the ECU doesn't mess anything up, quite the opposite in fact. The ECU learns its way round a failing MAF, and adjusts its learnt maps accordingly. This is a gradual process that takes a while, so to the unaware driver, everything's tickety-boo. However, when you reset the ECU, the maps revert back to factory defaults, and the failing MAF suddenly sticks out like a saw thumb.

 

Thanks to all it sounds more & more like MAF sensor The Judge hit it on the head - when I changed clutch had to disconnect battery so ECU would have reset. I am running panel filter so no changes with induction. Just 'cause I changed clutch thought it would be related to that - goes to show you.

 

Thanks Judge, it all makes sense now even to a novice like me!!!!!!

 

 

had this problem, turned out to be lambda sensor and not the MAF, replaced both anyway for the sum of 200 notes (gulp!)

 

I presume an afr gauge would highlight this problem ???

 

Would certainly highlight a fcuked lambda. But a failing MAF could take such a long time to lean out, you may not even notice it, as the AFR gauge wouldn't suddenly indicate lean. A knocklink would be much more useful. For instance, a lightly modified car could operate quite happily slightly leaner than ideal, and as long as the Knocklink was quiet, you knew (to a degree) you were safe. If you only had an AFR gauge, at what voltage would you say was too lean without knowing whether it was detting or not...?

 

OK so I need to get myself a knocklink as well as my AFR then ??

 

How modded is you car presently/going to be?

 

When you order/get then new MAF sensor make sure they only sell you the sensor part which is small and goes inside the main sensor housing.

The sensor part only should cost about 70 quid whereas the whole sensor + housing is about 200 squid!

My dozy dealer originaly ordered the whole sensor + housing until I told him he could order just the sensor (and he ordered one for the new shape 2001 MY t**t)!

Best 70 quid I ever spent!

2pin.

P.S. If you are planing to change it your self then make sure you have a driver for the tamper proof screws.

 

My MAFF is also on it's way out. Anyone know where to best place to get a replacement from and how much are they (94 WRX)

 

The car engine is only slightly modded just now Induction kit and dawes sevice but will be going further as cash allows so I think next purchase should be a knock link.

 

If you're increasing/controlling the boost manually, the Knocklink is absolutely essential. Add to that the induction kit (which can sometimes lead to MAF damage due to vibrations), and the Knocklink becomes vital...

 

I got mine from www.gradea-subaru.co.uk yesterday and cost me £80 plus vat.

While i'm on the subject can anybody tell me what the idle speed should be?
I hav'nt fitted my MAF yet but today its not stalling but just idiling a little lower than normal.

 

After being fully warmed up, mine's about 800rpm (UK MY00).