Quick question ... since a week or so, my Scoob almost stalls when stopping (at the lights etc..), then recovers, but hunts while idling (900 rpm - 700 rpm - 900 rpm etc...)

Lambdalink indicates very rich mixture (7 to 9 % CO)

I'm running a Unichip, so idling is controlled via standard ECU.

Could this point to a faulty lambda sensor, or is my engine on the way out ? Everything else works without any problems, it's just the idling.

Cold idling (at startup) does not seem to suffer...

Any ideas ?

Ta,

Theo

 

don't know anything about unichip, but it could be lambda sensor as you said, when is the last time you changed your spark plugs ?

 

Theo

I know its an entirely differnt engine but I had this on a Fiat Coupe turbo with exactly the same symptoms. I replaced the Lambda probe, Idle acuator valve and loads of other stuff.

It turned out after spending about £750, to be a blocked air sensor on the inlet manifold. I'm not saying the Scoob even has one of these, but start with the simple things unlike me.

Cheers

Nathan..

 

Yep, it sounds like the lambdasensor alright.
You should've gone for the Link Theo.

Cheers

/J

 

Sounds like the same symptoms as when the MAF failed on my car.

 

This is probably a long shot and probably wrong, but, could it be the dump valve?

Wrexy.

 

I too have seen this with a failed MAF which would be the Scoob equiv. of Nathan's "air sensor on the inlet manifold"....

Having said that, if the MAF goes then you usually get the Check Engine light come on. Perhaps the MAF is not completely duff yet...

Matt.

 

My check engine light did not come on when the MAF failed.

Wrexy, I've seen idle problems like this when the dump value is leaking.

Now that only 2342 possible causes of this problem.

 

Yeah, most likely would be the MAF, or the BOV - the lambda qould affect the whole range, not just the idle.

I'm leaning towards the BOV.

/J

P.S.
I could sell U my MAF...

 

Thanks for the replies...

Sam, new spark plugs NGK 7b went in 6 months ago, so they should be fine I guess.

Should have gone for the Link ? I hope my idling problems are just temporarily

SAM, I think you have the MAF & lambda mixed up a bit ... the lambda sensor only plays a part in the mixture off boost ... at the moment there is boost, the mixture is (for the biggest part) a function of MAF, RPM and load site (boost). Fuelling under normal driving is still spot on ... I think, because if the lambda is telling porkies, so would the Lambdalink

MAF sensor is new as well BTW (after I had a contaminated one from removing the resonator)

Dump valve ... I did not know it played a part during idling ?

When the engine is about to stall, you can see the ECU dumping in more fuel to keep it going (hence the high CO values), and it seems to work ... very strange.

I'll book it in at the dealer of course, but I just wondered if it was a known/straightforward problem. Guess not then ...

 

i also thought maf sensor at first but usually when it fails the car goes to safe mode kind of thing and you can't go above 6-7psi ?

 

Theo, I know the JECS runs open loop druing WOT and on boost...I don't know how you're running, but I'm not driving it all the time with the pedal on the floor.

I'm convinced it's the BOV, or a vaacuum leak somewhere.

Hussam>>The MAF can become dodgy, without going into **** up mode, but that wouldn't just cause problems at idle.



Good luck Theo!!!

/J

 

why do i have my sensors mixed up ? i only use one sensor so how difficult is that to learn ?

i don't know how the standard ecu work exactly but off boost i would have pressumed would be controlled by the lambda and maf sensors, maybe not. on boost is open loop. and your problem is off boost isn't it ?

 

Oh lol, Sam = Sam, SAM was Secret Agent Man I.e. the comment was meant for Jerry.

 

OK, a few takers for the dump valve theory ... would I be right in thinking I could easily test this myself ? If I block the return hose from the inlet manifold (just squeeze it ) to the dump valve when the car idles, the air would not "leak" back would it ? Or would the problem already exist before the throttle butterfly ?

I hate dump valves

 

The dump valve will only cause a problem at idle if the manifold pipe is spliut or off (small pipe connected to outside of valve not the large one)

When car is cold ecu runs open loop with enrichment so the lambda is not in play, the problem could be eiether lambda or maf, first port of call would be lambda as this certainly will be used for idle as the air flow over the maf is very low.

If its the lambda then it will have been runing rich over the whole of the lambda control range (up to about 0.2 bar afaik) but idle would be where you would notice it most, its possible for a lambda to just get "tired" and start to produce a lower voltage output.

 

Bob, thanks, makes sense.

I wouldn't have noticed the richer mixture up to 0.2 bar, as we leaned that out quite a bit with the Unichip...

I was thinking it would be the lambda sensor, but then I thought ... hold on ... if I see a 9 CO mixture on the Lambdalink, surely, it's the lambda sensor that is seeing that kind of mixture ?

Normal behaviour at idling is ... no lights on lambdalink ... then shooting to first orange light ... going back to no lights ... going up to 3rd red light ... etc. I believe that this is the normal way for a lambda control to behave ?

Now I just see 7 or 9 CO (last green lights).

In other words... I am confused now.

Surely the LambdaLink is seeing the same values as the ECU ?

 

Yes the lambdalink sees the "same values" so that would indicate that the sensor is ok and something else is at fault. That leads to the maf, could be contaminated and providing a false reading to the ecu which is taking the map point away from the range that the lambda sensor could correct. Could be the maf temp compensation cct is faulty.
Could also be a contaminated map sensor providing a false out put or the water temp (coolant) sensor, the one that feeds the ecu not the one that feeds the temp guage, could also be suspect.

Check the vac pipe to the fuel pressure reg, if its leaking that would allow higher fuel pressure at idle which would cause it to run rich there.

Have you also checked all the wiring connections from the Unichip to the factory harness, its a long shot but something may have come adrift there.

just some more thoughts that may help.

 

i had, word for word, identical problem on my old 94uk, i cleaned the MAF and also the idle speed control valve which was Gunged up with carbon.

 

Evil which Bov have you?

I have run a few bovs now, I had problems like this.

You have to check the following on the bov:

no leaks, splits, loose hoses to the bov

Check the Bov is not sticking open


Let me know which Bov


Moe

 

Thanks for the other leads Bob, I'm sure we'll be able to crack it in no time.

Moe ... I had an *cough* "uprated" recirculating dumpvalve earlier this year. We put it on because we thought the standard DV would not cope with the increased pressure (1.25 bar with a VF23). The DV has caused nothing but trouble after a while (open when it should have been shut, giving a whopping 0.2 bar of boost , and shut when it should have opened - great gearchanges though ).

In other words, we refitted the factory item, which does not give any problems at all (except maybe this idle problem).

I would have preferred to get rid of the DV altogether, but I don't think the VF23 can handle that.

It just puzzles me that I only have problems at idle ... a failing MAF would surely cause trouble higher up the rev/load range ? I looked carefully today, but the A/F values I see on the LambdaLink are exactly the values we have seen since the beginning.

Anyway, I have enough ammo now to suggest a few possible causes to the dealer, so I'm sure it will be sorted. Thanks for the info.

Edit to say the car is a MY99, which is important in relation to the type of standard DV that is fitted.

[This message has been edited by EvilBevel (edited 26 September 2001).]

 

Just to keep you updated, and for the record ...

When I phoned my dealer and explained what was happening, he replied ... "MAF sensor"

I wished the cure would have been cheaper but he was spot on ... the moment we changed the sensor, idling returned to normal, no more hunting or stalling ...

My filter looked pretty ugly, and I'm now back to the standard Subaru paper item, thank you very much

Oh ... and I get a bit more boost with that standard item, believe it or not

I took the failing MAF with me ... any chance of me cleaning this thing (MY99, so hot film type) ? Or should I just put it on the mantlepiece

 

Theo,

Good to hear it's fixed. I knew somehow I'd be wrong with my diagnosis, but sometimes with idling problems it can be the BOV. Not in this case but.

What induction kit were you using?

Cheers,

Wrexy.

[This message has been edited by WREXY (edited 28 September 2001).]

 

I'm glad to hear it's sorted Theo!!!

I can't even remember how it felt waiting for the MAF to go ****'up with the PX induction kit.

/J

[This message has been edited by SecretAgentMan (edited 29 September 2001).]

 

I had exactly the same problem with my STi V 4 dr last week. At traffic lights it would nearly stall then rev to 900 then nearly stall in a cycle. If you held the revs at say 2000 for 5 secs it would get back to normal. I suspected a contaminated MAF sensor or shot spark plugs and when I took out the ITG filter I could see it had contaminated the air flow. The mesh filter in the top of the air box was black with oil from the filter and when I took out the MAF sensor it did look a bit grimy in the wires at the end and the film. I cleaned it VERY CAREFULLY with something called Servisol Aero Kleene (an aerosol isopropyl alcohol cleaner for electrical contacts and tape and video heads and such - a couple of quid from maplin, RS or similar), and a piece of kitchen roll. It didn't seem to clean off a great deal of muck but the film did look shiny again when I'd finished. Put it all back together with the old paper filter instead of the ITG and went for a drive. Seemed much better than before at the top end and didn't do any of the erratic idling either. Did that on sunday and so far it hasn't come back. I'll be keeping my fingers crossed but I'd recommend to anyone that they try and clean the MAF sensor before spending lots of money on a new one (at your own risk though or course!). I also wouldn't recommend using an oiled foam filter. I'll be sticking with a regularly replaced paper one from now on I think.

cheers,

Eric.