Ok, its not a problem as such - but something thats been annoying a tiny bit of late with the car.

KL - AWD (Auto) - Sprintexed.

A lil background:
Last month - the car wanted to be collected by tilt tray and have more money spent on it due to the SC.
When I got the car back, they said that they had adjusted the idle up a bit because it was trying to idle really low - and theatening to stall (even tho there had been an ECU reset...)

Fast forward a couple of weeks, base idle seemed to have settled back to roughly where it used to be in N at the lights - roughly 800ish RPM.
It always fluctuated a little even before the blower went on - thats not my concern with it atm.

My possible concern, is that when im coasting / braking up to the intersection, the tacho will rise and fall roughly 500-800rpm while slowing / coasting.
If i put my foot on the brake - the fluctuation is less
Once I slow down enough, the tacho will hold steady / idle where it should normally be

The car will also, on occasion - decide that no - 800ish (lets call that normal RPM) is too high to idle - lets try 500rpm....

It can it - hot or cold ambient, night or day, hot or cold coolant temp, high or low speed lift off accel/coasting
It appears random - sometimes itl do it every time you coast, others it doesnt hunt.

Could it be as simple as the ISC starting to call quits to the occasion?

Car has 143oookm on the clock now, and is serviced regularly every 5ooo KM - all items that need replacing get done straight away.

Thoughts please :)

My possible concern, is that when im coasting / braking up to the intersection, the tacho will rise and fall roughly 500-800rpm while slowing / coasting.
If i put my foot on the brake - the fluctuation is less
Once I slow down enough, the tacho will hold steady / idle where it should normally be
Thoughts please :)

My TL behaves exactly the same when slowing down - I figure it's simply the auto changing from 3rd to 2nd on a trailing throttle........also when coasting down a slope not intending to slow/stop, revs will drop and car speeds up as higher gear is selected (automatically).
My wife's New Beetle auto behaves the same.

i had that recently on our Delica , it was the alternator bearings , they were so tight and almost seized up ruining the belt.
fix alternator , no more idle problem. worth checking anyway.

Alternator sounds interesting.

Since the fluctuation reduces when you brake, I think it's the vacuum/boost causing the fluctuation.
Maybe the SC is providing enough boost that slips past the throttle body, but using your brakes uses the vacuum behind the TB and doesn't let that seepage happen?

Or here's a more complex idea: (Magna has a MAP sensor, doesn't it? If not please substitute correct name below :) )
When the throttle is closed there should be no air going through the intake.
But maybe your SC is boosting a little and causing the intake side to pressurise and the MAP sensor thinks you've opened the throttle, so ECU adds fuel, the engine doesn't really have any air to burn the fuel, so it chokes and rpm drops. SC stops boosting at 500rpm, air pressure returns to normal, RPMs rise back to 800, SC pressurises the intake again and you're in a loop.

If that's the case, I can think of 3 ways to try and stop it -
1) relocate the map sensor so it's less affected by the pressurisation - this would mean having it right next to the throttle body.
2) overide the map sensor's values so that it ignores low pressure changes - this will make the car drive differently though - probably more snappy.
3) a blow off valve. If it has to plumb back to the intake, then maybe it could bypass the map sensor.

I don't know why, but I always read what you write about your car. I want to hear about more fun and less repairs though! :)

Hye guys, sorry its been so long since I have been on here - been flat out at work, getting really draining and tiring there now!
anyhow.

Never considered the alternator - could be a possible cause to my issues, in that i ran around for a year without the full R/H Front wheel arch liner installed to my car - you could look through my mag wheels, and see Air Conditioning Compressor, and oil filter, so maybe a bit of crap has gotten into the Alt.

Might get it inspected - just in case.

Sprintexes are positive displacement - that is, it doesnt have to be doing 3000rpm to create additional pressure (boost) to the charge, essentially its always on boost in a manner of speaking (though not really at idle i should hope!!!)

I think that the BOV bypasses the MAP - not 100% tho, think it does, as it looks to dump boost prior to the SC housing.

Was having another thought - perhaps the TB is clogged up with crap and needs a clean, might be a slight possibility (running around with the 7th injector almost permanently on... couldnt have been good for the cleanliness of it all)

Was talking with a mate of mine today over coffee, he suggested Idle Speed Controller as an option / possible fault.

Geting the car wheel alignmed Friday - will get them to inspect while its there.

ISC is a 10 minute job. so to replace it and doesnt work, well, it's only 10 minutes.
there will be air entering your motor at a closed throttle as when its at 0% TPS the ECU will detect an idle state and that's when your idle motor will start working, it'll use the bypass air passage in the TB to provide a bit of air to the engine to keep it running. Let me know if that is wrong as I am almost certain that's how it goes. Couldnt hurt to take the TB off and give it a good soak in carby cleaner.

Mine, when its in smart-engine-brake mode, will idle up - check speed - then either downchange or continue in current gear until speed is OK. There is on hill near my house which I can replicate this on all the time, not that its a fault (I love that it will engine-brake, saves me knocking it back to 3/2)