intermittent rough idle and low boost presure

CR41G

CR41G

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Every now and again my boost presure drops from 9 psi to 3psi and will stay like that until I turn it off and back on again then itll b fine for a few days or weeks.
also it will idle very roughly .. not hunting but definatly bouncing again it happens every now and again and not all the time ..

Any ideas?? Im goin to remove the throttle body and give it a clean over the weekend and see how that goes
 
Its a 2002 a3 1.8t sport aum engine.
theres no fault codes to report

the boost issue is interesting .. it doesnt matter weather the engines hot or cold .. I could be driving for say half hour and all would be well .. say I stop at a shop for 2 minutes and start it back up and then its not going above 3psi but if I turn ignition off and back on again its back to 9 psi.

the idle issue can happen completly randomly and again does not matter weather hot or cold but this can happen at any time .. again on a 30 minute drive it would be fine .. then stop at a random set of lights and its bouncing round and even though its not affecting boost presure the car feels flatter and a little slugish ... with this turning on and off does not clear the problem ... the interesting thing is it comes and goes very intermitant .. it can happen once every few days or every couple of weeks .. same as the boost issue
 
I have an exact same issue... Be good to know ideas for looking as no fault codes either. What is ideal to use as I have a cable for me phone... =]
 
Odb 2 code reader .. no eml and no fault codes .. it just happens .. the boost issue seems a totally different issue to the idle one .

im gunna remove throttle body and give it a good clean see if that helps .. could be idle control valve full of ****?

As for the boost im not sure Ive had a look at the vac lines and cant c any **** ones .. could it be a waste gate or n75 valve fault?

Cheers
 
Update and im an idiot!!

When I checked the vac lines I didnt tighten up the jubilee clip that connects the TIP to the MAF and it had pulled off the MAF at the bottom allowing unmetered air into the system doh!!

I think that may cure the boosting issue and I think the MAF is the idle issue ...it was idling like crap earlier so poped bonnet (thats when I realised about the TIP pipe) and pulled the wiring plug off the MAF and it took a deep breath and started idling fine!!

Is that a sign that the MAF is kaput??

Cheers
 
Give the maff a blast with some brake or carb cleaner, it may just be dirty, especially if the car has had an oiled air filter( K&N and the like), when you clean the TB, do not disconnect the wiring, place a brick on the throttle pedal, then turn on ignition to open the throttle plate, clean right in the corners with cotton buds soaked with carb cleaner, also do the air intake temperature sensor at the same time.
 
Was going to ask about that .. I had a look on google and it was saying it will need realigning??

So if I remove the tb from the inlet but leave the electrical plug connected it shouldnt need to be realigned??

as for the maf .. I do hav a performance air filter but its an of the s2000 variety which I dont think is oiled.

cheers again
 
If say I have unplugged the throttle body... What's actually wrong with doing so?
 
Just read that the realignment procedure is quite simple. I may perform this just for minds sake =]
 
Simple if you have vagcom .. which I dont so best left plugged in for me.

Took mine for a descent drive down some national speed limit roads and now it seems all good again .. idling fine .. boosting fine .. generally running all good.. im guessing after sorting the intake pipe being loose and pulled off slightly that the ecu has sorted itself out now theres no unmetered air being sucked in and the system has settled back down.
im still goin to give the throttle body and air temp sensor a clean but for now im just goin to see how it goes.

had a ****** punture this morning aswell .. took it for repair to find out the inner tyre wall was split and miss shapped so new tyre fitted .. ownership of these cars now there geting on a bit is interesting ha ha..but no where near as interesting of my old mgtf .. I was underneith that thing every weekend !!
 
Update
Removed and gave throttle body and a it sensor a ****** good clean ... after 50 miles the car spat it's dummy out idling constantly rough and eml came on.

Now I plugged my code reader in and it came up lambda sensor bank 1... I cleared that fault code and the car instantly started to idle spot on but simultaneously the tc light came on so rescan and it's now saying maf sensor fault ... but now the cars behaving itself and idling fine .

So is a new maf on the cards??
 
Maf sensors can fail out of the box... did you buy a bosch replacement or a 3rd party?

Question to forum users regarding idling issues. Is an agu engine its totally dependent upon the maf?

My troubles started when I simplified the oil breather system and vented to air which I have now put back to oem as my rings are going and there's loads of vapor =] fun times. Secondly whilst I was on the quest to rectify the idling issue I changed my MAF for an vr6 2.9 one. On the premise that if I have to buy one one why not get an upgrade... now my boost won't go above 5psi. Coincidence i'm not sure due to only just fitting a boost gauge. i'm awaiting my vagcom reader to delve in deeper to fault codes.

My idea was to replace the sensor back to oem but keep the 3" maf housing. will this be benificial or not...?
 
You need the electrical plug connected so you can open the throttle plate, if you move it by hand you can damage the motor, also you won't have to re align the throttle.
 
Haven't replaced the maf yet.. and I don't have an air box because I've done the s2000 air filter mod.
I've tried cleaning the maf but it made no difference.

The lambda fault could be that I've put higher octane fuel in it for the first time and added redex fuel injection cleaner (which I think I've put to much in) so not really concerned with that.

It's looking more likely the mafs nackered so just goin to get it replaced and take it from there.

On the plus side I think the cars much happier on BP ultimate than super market 95 Ron and seems much more responsive than on cheap fuel
 
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