Quote:
Originally posted by Mr. Pockets
IRIS stands for 'Inertia Resonance Induction System.' I've attached the page from the R&T Guide explaining the valve. To me, the explanation always sounded a little low on actual information - saying how IRIS is different compared to normal variable-intake systems in operation, but never how it really does what it does.
I never figured that the IRIS valve did a whole hell of a lot. But then, other parts were designed around its use - the intake plenum and dual throttle bodies - so maybe it really does serve more than a marketing function.
I didn't know until reading this thread that the IRIS was vacuum-actuated. Maybe the valve doesn't work on some SVXs, and that's why those cars feel 'sluggish.' Maybe it's an intermittent problem on others, explaining why sometimes the car feels ultra-fast and other times not so much.
I have never given any credence whatsoever to claims that Power Mode did anything but change shift points. Also, I've never accepted anybody's claims that their car sometimes feels like it has more power than other times. But maybe this would explain those claims.
I know that the ECU determines when the IRIS closes or opens, but would it know if the valve didn't open when it should, or was stuck open?
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The IRIS thingy is not vacuum operated, but when it works it affects the intake manifold pressure. It is opened or closed on command from the ECU by a device called the induction solenoid valve.
Good question Pockets as to whether the ECU knows if it is malfunctioning. Presumably it must, but our error codes do not show a fault number for this solenoid. It is possible to check if it is operating properly. The Service manual lists pin 20 on connector B62, and it should read 0 for ON and 13-14V for OFF.
Whether the ECU switches it open or closed is determined by engine speed and fuel injection quantity. However, from the chart in the manual, it would appear it normally is closed at low engine speeds and open at high revs. The point at which it should open for optimal volumetric efficiency is about 4200 RPM.
I have seen posts from people with two cars saying one car goes sweet at high revs, but the other has more pulling power for driving at low revs. Stuck valve or inactive solenoid could explain this all right.
BTW I was not suggesting that the different shift map did anything other than change the shift points. However, in POWER mode you do get more eager access to about 50 hp that is available higher up the rev range. In NORMAL driving on two trannies now, my car shifts up at
000 RPM, never allowing the use of those extra horses without forcing kick-down.
Joe
