lukeuey

Hi,

My car is a 99-00 impreza 2000 turbo completely standard, I was out and about in her the other day and everything was fine. I hopped out for 5 min in town and when i started er back up again check engine light. I drove it home carefully (about 4 mile) and plugged the diagnostics wires together under the steering wheel, got error 23, maf sensor. The car seemed to drive fine however, was idleing perfect no hunting just when got er up to about 3-4k revs all of a sudden spluttering, juddering and wont go any more what so ever. Thried cleaning the maf with electrical cleaner and air duster no change.

I left er tick over on the drive till the engine was at operating temp then disconnected the maf, didnt stall or make any difference what so ever to the running so im pretty sure the mafs nackered, im just wondering how come she will idle perfectly no huntingor stalling or anything and drives fine at lower revs then all of a sudden you get to this point and severe juddering etc wont give anything more. Does this sound like it could be just the maf sensor. Last car i had that had similar prob was bad HT leads tested sparks from coil pack all fine and the engine def drops power when disconnecting each one so i assume the leads and plugs are ok.

I dont have a compression tester, could i have a nackered cylinder? or am i just worrying to much do you think and just need to replace the maf. I just thought a broken maf would effect the engine performance from idle right through rather than just over a certain rev range, the car isnt smoking and sounds like its ticking over fine at idle. Has anyone had similar problem before?

Thanks for any help

Luke

TonyBurns

iTrader: (3)

If you have code 23 then its pretty much picking up a maf sensor fault, 2 ways of sorting this out, dealer diagnostic and then a new sensor, or just buy a new sensor, though I would go for the diagnostic to be on the safe side incase there is any other issue there

Tony

Pedroturbo

let us no how ya get on luke, cheers

Splitpin

It would've bee worth you hitting Search prior to post, as everything you need to explain what has happened to you here (and how to fix it) is already out there on the forum. If the check engine light came on and stayed on the entire drive, and code 23 was the only one you got in read memory mode, your MAF sensor almost certainly has failed. The reason why the car seemed to drive okay is because when the MAF errors out, the ECU is able to replace the actual mass airflow input with a calculated substitute, as a get you home measure. The reason why it mucked about at higher engine speeds is firstly because that calculated substitute only works at low revs and low throttle, and secondly because it would have been in limp mode - with a rev limiter causing the "spluttering".

That's hardly surprising. When the 99-00 sensors fail it is almost always because some very tiny wires inside the sensor body have fractured. Clearly, under those circumstances, "cleaning" will make no difference at all.

Why did you do that? If you read some post on here about unplugging the sensor with the engine running, and if the engine stalls, sensor is good, if the engine doesn't stall, sensor is broken, the bad news is that it's bullsh*t. Clearly in your particular case the sensor is broken, but you already knew that from the check engine light and 23 code. This "test" proves nothing other than the ability of people to be able to spread well-meaning disinformation on the internet, unfortunately.

Once the code 23 error comes on (and stays on), as far as the ECU is concerned, the sensor is already unplugged. That's why physically doing so makes no difference to the way the engine behaves. The big problem with this "test" is that it will usually pass heavily damaged (but not quite completely knackered) sensors as "good". Which is a serious problem as it's sensors like that which are most likely to blow someone's engine up. It will also "fail" brand new sensors, while unplugging a perfectly good sensor with the engine running actually has a small potential to damage it, just to indicate how useless this "test" is.

It almost certainly is. The only other possible explanation for these symptoms is that the wiring loom to it has been damaged. It's far more likely for it to be the sensor than the wires - although there's no harm in you physically inspecting them, or even checking them if you have access to a multimeter.

As above when the MAF signal drops out for more than 0.2 (or 0.4, I forget which) of a second, the ECU sets the error state and then calculates a replacement for the air flow value by looking up a 3D map that is indexed by engine speed and throttle position. The reason why it doesn't hunt or stall etc is that this "guessed" figure is much more stable than the dodgy, fluctuating input you get from a failing MAF sensor. It's the fluctuations and drop-outs in signal you get from a failing (but not yet totally failed) sensor that causes the hunting and mucking about.

Because, as above, you are now in limp mode and the rev limit has been dropped right down.

If it ain't the wiring, it sounds just like the sensor, yes.

None of what you are describing above is consistent with a damaged cylinder. Although, the downside of being in this position is that it's quite likely that your sensor was degrading for a period of time before it actually failed. The problem under those circumstances is that a failing sensor usually makes your engine run leaner (and also makes it feel more powerful, so you'll be more likely to enjoy it).

So, it's possible that you may have inadvertently given the engine a hard time before you actually became aware of this issue. However, ultimately it's not worth worrying about. If it's happened, you'll find out about it, eventually. Until then, concentrate on what you know is wrong and go from there.

You do need to replace the sensor, yes. Part number 22794AA010, a bit over £100 from your local Subaru dealer, a little less from somewhere like Import Car Parts or AS Performance. Reset your ECU after fitting it.

Yes, loads of people. Everything I've written in this post could have been found if you'd hit the search button and spent a few seconds thinking up a suitable query.

lukeuey

I have searched and stressed over this problem for a week, im not a mechanic, i have poured over posts about all sorts all over the internet and also posted on the SIDC forums days ago where i was advised to unplug the maf to test it. I cant afford to throw £100 on a already nackered engine so i thought id post first here my exact problem to get some opinions before ordering especially after reading posts about mafs nackering cylinders and faulty coil packs and plugs. My girlfriends dad also had a maf error flash up a few months ago on his and put a new one on and it didnt fix the problem and it still persists from time to time, I have also read posts on other boards who have replaced there maf only for the problem to continue and be something else, all this served to make me more cautious about wasting £100 not that i hadnt bothered searching because i have done, and like i said im far from a mechanic, everything i mentioned in my original post was information i had found out just from searching boards

Anyway thanks for the information its exactly what i was after i shall now order a new sensor.

Thanks again

Luke

smokingkills

iTrader: (3)

Luke, I think you'll struggle to get a new one for £100. Stay well clear of non oem MAFs too.

Splitpin

Right. Could you do the Subaru community a favour and post back on that thread over there, thanking whoever gave you the advice but saying that you've been told elsewhere by someone who knows what he's talking about that this "test" is a load of b*ll*cks and cannot determine the difference between a good sensor and a naffed one. Post a link back to here if you want. Unfortunately this "test" is downright bad advice and will cause more harm than it will ever prevent. Hence if you can do something to prevent well-meaning people spreading it in future, do it.

The bottom line is that you might have damaged something as a result of driving around on the failing sensor before the ECU detected it. However short of disassembling the engine to check, you have no way of knowing, so you may as well just replace the sensor and keep your fingers crossed for a bit. You don't really have any practical alternative.

Hmmm. You should advise him to get that sorted out, ignoring it is asking for trouble. As per previous post, pretty much the only other thing other than a duff sensor that can cause the code 23 error on a classic is a fault in the wiring loom, either the power supply to the MAF unit or the signal/ground wires running back to the ECU.

No sweat. That's what the forum's for.

£105 plus delivery here. Stay well clear of the dark side, oops, secondhand/used ones too Luke. New genuine one only if you want to be able to rely on it.