MIAMI

iTrader: (1)

Hi guys just need your advice, ive got a sti 6 1999 and whrn i drive the car normally and come to a juction after breaking the revs drop right low like its going to cut out then jumps back to life and idles fine, no probs with the car, starts fine etc. no engine light on.

thanks

John306

id like to know about this as my 97 wrx is doing the same after having a rebuilt engine fitted. it didnt do it before but it did have a new crank sensor as the old one broke coming off my old engine, could that be anything to do with it?

bulldogtwy

sounds to me look it could be a MAF sensor as your slowing down air flow decreases and it may be missreading causing dip in revs. get it plugged into diagnostics to be 100%

MIAMI

iTrader: (1)

Cheers guy, i did have the engine light come on a few moths ago and it threw up code 22 knock sensor when i was driving on motorway and the car held back and then the light went off and car was ok so i reset ecu and its been off since just started it and the engine light was on straight away and kept blinking on and off and then stayed on for a few mins.......took the car round the block and the light went off....read the code and code 22 again.

going to test the knock and maf with multimeter and will report back asap...

TonyBurns

iTrader: (3)

Is it a version 5 (1999) or a version 6 (2000)? no real differences except you have to depress the clutch to start a 6, but giving 1999 as its year (they go by model years, not registration years) can confuse things a little

If the maf has not been changed (any other mods on the car? remapped for uk fuel, induction kit etc?) then its worth while just doing that for safety reasons, fairly cheap at around 110-120 quid.

Tony

bulldogtwy

If you drop me your chassis number mate i can get you a price on these parts if you want? but as tony said itl be worth changing it anyways.

MIAMI

iTrader: (1)

Hi tony, its definetely a version 6 as its dip clutch start and checked the vin number. But no real difference like you said.

Its got a fmic, vf35 turbo decat blitz nur exhaust and been remapped by legendary alan jefferies using ecutek.

thanks for the advice very much appreciated.

MIAMI

iTrader: (1)

I'll get you chassis number when i get home tonight at about 6. if you could get us a price then that would be great. i love scoobynet.

bulldogtwy

is it just the MAF you want a price on mate ? and its a 1999 sti?

tamboi

I have a 93 imperza and mine is doing the same, revs droping right down when breaking but sittin ticking over fine and no engine light, I have been told it may well be the maf sensor to.

MIAMI

iTrader: (1)

Hello mate, please could you get me the price for both the knock and maf.

the model number is gc8g4ed but ill be home and get the chasis number later for you fella.

bulldogtwy

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cheers

ALi-B

iTrader: (1)

Please before forking out, check for minor vacuum leaks - this is a prime cause of this problem as it causes the MAF to read incorrectly but not severely enough to the extent it puts on a CEL light.

Plug-in diagnostic checks will not reveal vacuum leaks, as the sensor (MAF) being checked by diagnostics is the same sensor being fooled by the air leak. Bear that in mind when reading fault codes.

You'll know you've wasted your money when you fit a new sensor without performing such checks and realise the problem is still there.

Basic checks includes all the induction, interccoler, boost control pipework, brake booster, and also the dumpvalve pipework. Any hoses that are perished or showing signs of cracking need to be replaced, and ensure all push-on fittings fit tightly, if not use hose clips or replace the pipe.

Also ensure the dumpvalve itself is not leaking and if it is a vent to atmosphere type valve, it needs to be closed at idle and low engine speeds. If it is an aftermarket dumpvalve, it may well need adjusting to prevent it opening prematurely. Better still - if you have the original factory item, refit it.

Finally ensure the plastic hose under the intercooler (if still fitted) is in sound condition, these are prone to splitting. Whilst a large split will cause obvious issues, a minor split can go unnoticed, except for slight idle issues.

Alternatively find someone with a smoke tester which will visually test the inlet tract for leaks.

If the car is runnining a cone filter, especially a sponge or steel mesh type, then teh MAF will be contaiminated with dirt.

bulldogtwy

sorry about that i didnt realise guess i should have read the rules lol

MIAMI

iTrader: (1)

Thank you for the reply Ali-B very much appreciated. I have already checked all the pipe work as this was first protocol like you said it may well be a small leak but none have been found. i do have a cone filter mesh type so will take apart. Ive been told that you are not supposed to clean the mafs on 99 cars as they are delicate. the enhine light comes on intermittantly. Can you clean the maf or just leave as is?

bulldogtwy

im pretty sure you can buy MAF cleaner some were but cant remebr who makes it lol

MIAMI

iTrader: (1)

cheers bulldog, ive got a memory like a goldfish and cant remember myself sometimes, thanks alot for your assistance.

bulldogtwy

no probs mate hope you get it sorted and it dont cost to much.

Splitpin

Is the engine properly mapped for this "cone filter"? If not, and especially if you are still running the standard mapping, the best thing you can do right now is to get rid of it and refit the standard airbox/resonator/intake. Poorly designed and fitted induction kits can accelerate sensor wear as well as causing dangerous misreads, if the ECU hasn't been reprogrammed with altered airflow scaling.

There's a lot of bullsh*t talked about this subject. In general the concept of "cleaning" an airflow meter is pointless, given that your air filter should already have removed any particles big enough to damage or contaminate it. There is no such thing as "MAF Cleaning Fluid", btw. The bottles you can buy on eBay etc. sold under that name will contain water/alcohol/brake cleaner or some other cheap standard solvent sold at a huge mark-up to people who don't know better.

In any case, the common mode of failure on the 99-00 airflow meter is vibration causing the tiny wires that connect the metering cell to the signal processing circuit board to fracture. Under these circumstances no amount of cleaning will cure the problem, as the damage is physical, and internal to the sensor unit.

What trouble code(s) do you get when you connect the black plugs?

If you cannot, as Ali has already suggested, find any air leaks or similar explanations for this misbehaviour, the safest way forward is to assume the airflow meter is failing and replace it. Part number 22794AA010 either from your nearest Subaru main dealer, or cheaper from somewhere like Import Car Parts or AS Performance. And don't drive under boost until you've replaced it. At all.

As above, if you haven't had the car mapped for that cone filter, ideally get rid of it and replace with standard parts before you fit the new sensor.

MIAMI

iTrader: (1)

Hello splitpin, thank you for your time first of all, the car has been mapped with the mods done first and mapped using the cone filter.

this was done by alan jeffery.

Any advice on here is taken and appreciated and will try to get down to the bottom of this issue.

When the black plugs were connected the only trouble code that cam up was code 22 (knock sensor). I will of course test the sensor using a multimeter but as this is a intermittant fault may be difficult.

Any more advice will be helpful.

bulldogtwy

if the knock sensor was at fault before mate chance are it will be that! but cant be 100% thats the problem you get with intermittent faults.

Splitpin

Good to hear the filter is properly mapped in, that rules out one possible causal factor.

There is little point testing the airflow sensor with a multimeter, as you will have no way of knowing whether the output you are seeing at any given moment is correct/what it should be, and most multimeters are not responsive enough to display the drop-outs that characterise the "fractured wire" type of failure. For that you'll need either a storage oscilloscope or a datalogger.

Unfortunately, most MAF sensor failure modes will not cause the code 23 CEL either. The activation criteria for this error within the ECU are so loose that they will basically only pick up either no output at all, or a short in the wiring loom.

Somewhat annoyingly, there do seem to be a few cases where a faulty MAF sensor can cause the code 22 error. I don't know why this should happen but trustworthy, reliable people have reported it. Therefore, the fact that you are getting 22 adds to the suspicion. Although the first thing you should do in these circumstances is to check or replace the knock sensor.

You *can* check the knock sensor with a multimeter. Set it to resistance mode and see what you get across its two pins. The correct number should be 555Kohm +/- 5% or so. There should also be a direct connection (i.e. zero ohms) between the right hand pin as you look into the plug with the sensor upright, and the metal part of the sensor body. Be aware though that even if this sensor passes a static resistance test on a multimeter, it's still possible (albeit remotely) for it to be damaged. If you see any cracking in the plastic body, in particular, precautionary replacement is advisable.

Incidentally, this rev drop-down you're getting when you pull up at traffic lights etc. Is it noticeable at very low speed? If so, there is one test you can try. Get to a point where the engine is misbehaving, switch off, pop the bonnet and unplug the airflow meter and restart. You will see the check engine light on constantly. Blip the throttle gently, and drive the car around slowly at no more than parking speeds, paying very close attention to the idle stability. If it has noticeably improved with the sensor disconnected, switch the engine off again, reconnect it, and order a new one immediately.

BTW, speaking of tests, at some point, someone may turn up here talking about a test that involves unplugging the sensor with the engine running and seeing whether or not it stalls. If so, that test is bullsh*t and proves nothing, one way or t'other, and can, if you're unlucky, cause damage. Don't go there.

Also, meant to add in post above, if/when you do fit a new sensor, reset the ECU before driving on it.

Splitpin

A faulty knock sensor cannot cause misbehaviour at idle of the sort Miami is reporting. As I mentioned above, if the #22 error presents, the sensible first step is to check and rule out any obvious problems with the knock sensor circuit, but if this checks out, and there are no other discernable causes, suspicion falls squarely back on the airflow meter.

Oh - one more thing. Miami - does your MAF sensor have a stripe of green paint across the top of its mounting flange, where it's bolted to the metal bracket? If it doesn't, replace it straight away as it is at least six years old and one of the older type sensors.

If it does have the green stripe, use a mirror to look at the four digit date code printed in white ink on the lower rear face of the flange. If the first digit of the code is anything smaller than an 8, I would, again, replace on spec without even bothering to diagnose any further.

bulldogtwy

I know the knock sensor wouldnt be the bause of his issues but its still a problem worth checking is what i metn to say mate lol was about to mention about the date on the part. MAf's are farely common to replace on classics. its a farely cheap fix if it is the problem may be worth jus replacing it any way.

MIAMI

iTrader: (1)

Hi splitpin, drove the car and when in slow speed the car isn't doing the drop in revs but I gave a bit more throttle and came to a stop at a junction and the revs groped right down to the bottom and picked up.

The mad does have a green stripe and I'll post a pic as some of the White serial number is worn away.

MIAMI

iTrader: (1)

ive added the image of the serial numbers on the maf it seems like it starts with C36-700592.

Splitpin

That number's not the one we're interested in. As per my prior post you need to use a mirror (etc) or undo the two larger S-torx bolts and rotate the sensor in its housing until you can see the four digit code printed on the lower part of the mounting flange.

MIAMI

iTrader: (1)

ok i see, i will get hold of it tomorrow. thank you

harvey

iTrader: (48)

On an OE Classic you can adjust idle control as an interim measure to improve the situation and give the car another 100 rpm tickover.
The car mapped by Alan Jeffrey sounds like it may need a map adjustment if the MAF sensor is OK.

MIAMI

iTrader: (1)

Thanks for your input harvey....im going to see if the maf sensor on the car is the old type and then take it from there ....i may just need to get a maf in the end but will do a little more investigation into the fault.

The thing is i live in lancashire and its a bit of a treck down to alan jeffrey....so i may need to get hold of a mapper around my area.

Anyone got any suggestion on mappers?