Mass Air Flow Sensor problem - Classic STI
 

I have an STI v2 (1995) Classic Impreza import that done 67,000 miles. Recently I notice the car was miss-firing and cutting out. I did a diagnostic test which reveals fault code 23 (Mass Air Flow Sensor).

I've take the sensor out to have a look at it and it looks very clean. Questions..

• Can I clean the sensor with http://www.halfords.com/webapp/wcs/s...egoryId_255223

• Can I replace the sensor on the unit only. Looking at it there's no obvious way to remove the sensor from the unit
• Any recommendations on where to buy a new sensor (If it can be replaced) or the entire unit. Looking on line they are +£250
• Can I drive the car with the sensor disconnected? (limp mode)

Many thanks

Iceman_II (Phil)

Try & clean it very carefully 1st . While your at it clean boost pipes to. There will be more experienced people along soon to help I'm sure. :EVO:

do NOT drive the car with the MAF disconnected or knowingly failed..................

as for cleaning yes you can attempt it carefully but do not be tempted to touch the actual probe
as for the sensor its a complete unit and i have a few s/hand ones if your stuck.......should be a GREEN label version

Hi ASP, just given the MAF a clean. I'll take the car out tomorrow and see what happens. Might be interested in picking up a s/hand unit. I've sent you a PM to discuss.

Cheers

Iceman_II (Phil)

Ok 20 minute run and car seems ok. I'll keep a close eye on it for the next couple of days. If it happens again I think I'll have to replace the MAF.

Ok problems returned. :brickwall: The car will drive ok for 5 minutes and then complete loss of power. Engine light pops on, power steering dies and I then just have to start the engine again. Is this the normally what happens when the MAF has a problem?

Did a 6 mile journey to work today and the engine cut out on me 3 times. Not fun when your going round roundabouts :angst:

Iceman_II

If you heel toe is it still cutting out?

I can just about drive the car at 25 mph but the revs are dropping and it feels like the car will cut out at any time.

I've ordered a new MAF which hopefully I will get this weekend. If I still have the problem then I'm thinking its either an Air leak or a problem with the spark plugs.

Any suggestions it how to check for an Air leak?

Cheers
Iceman_II

if that dont work may i suggest a pm to cj he is not too far away from you

No joy with the new MAF. :sadnod: Car feels very underpowered Almost like its hunting or the timing is off. Also power steering feels like it's only working at 50% capacity.

Used butane gas around the vacuum pipes but no change in engine noise. If there's a leak it's not on the top part of the engine bay.

Anybody got any other ideas? I'm thinking ignition coils or maybe the spark plugs to check next.

Just swapped out the ignition coils for an old set and same problem. Is there a sensor on the car which could cause the diagnostic test to throw a fault code 23 even though I have replaced the MAF itself?

have you actually re-set the ECU since fitting the new item???

Hi, yes I have, I've disconnected the battery for an hour and also done the black to black/green to green, press the gas pedal fully down, hold at 50%, release and then drive the car normally. The car resets to the normal constant flashing but feels like it's not getting enough power. Almost like the petrol to air mixture maybe wrong.

I'm still thinking it's an air leak but finding where is proving difficult. I'll take the intercooler off next to see whether there's any issues with the pipes.

could be a fuel pump failing, common on early classics IMO

Found a problem where one of the pipes was disconnected under the inlet manifold. Here's a picture showing the pipe disconnected.

http://i1008.photobucket.com/albums/...n/IMG_2762.jpg

The pipe pushes into a bigger pipe to the left of the picture. So I've push them together.

http://i1008.photobucket.com/albums/...n/IMG_2765.jpg

I'm not sure whether the pipe will hold. Maybe need to see if I can get a cable tie in there (not much room).

I'll test the car out of the next couple of days and report back. Hopefully I haven't caused too much damage to the engine!

Car is back to normal again. :crowman:I can get back to racing those Evo's again.

Thanks everyone for your advice. :thanx:

Looks like I may have spoken to soon! Still having problems so I've bridge the gap in the breather pipe with some 13mm silicon pipe and jubilee clips but the car is still hesitates when driving. I'm now suspecting it could be the lambda (O2) sensor. Is there any way to test it before spending the cash on a new one to find it hasn't fixed the issue?

I believe they are located under the car near the exhaust pipe. Are they easy to access and replace?

I've replaced the MAF and Ignition coils so far.

It won't be O2/Lambda sensor if it's on boost hesitance, as the Lambda is only used for idle/cruise conditions.

Thanks SilverSurfer.

It definitely feels like the car is "hunting for power". I went for a 20 minute drive tonight and when I arrived home I left the engine running and lifted the bonnet. While my hands where on the bonnet I could feel that there's was a slight change in the engine power output which was cycling every few seconds. The change was not huge but definitely there.

Interestingly, and this might be related, the power steering feels quite heavy when driving. Is this linked to the power the engine is "not" putting out?

with a car that has no problems, when you idle, if you pull teh steering wheel a quarter turn, the engine revs will change momentarily to acomodate the load on the steering pump so I guess if there are problems with the power steering, i guess it could be your problem.

try removing the power steering belt and just let the car idle and see if the problem persists. obviously don't drive it with the power steering belt off