Need help with nested sub query

hi,

I have a recordset like so,

DT VEHICLEID NSEW
03/08/2004 08:30:16 169 IGNITION ON
03/08/2004 08:35:33 169 IDLE
03/08/2004 08:40:17 169 IDLE
03/08/2004 08:45:51 169 IDLE
03/08/2004 08:50:23 169 IDLE
03/08/2004 08:55:29 169 IDLE
03/08/2004 09:00:16 169 IGNITION OFF

what I am trying to do is count the idle instances between an ignition
on and an ignition off instance. I also want to work out the duration
in time between the first idle instance after an ignition on and the i
gnition off.
However I thought I would leave this until I find out where I am going
wrong with the first part of my query,

this is the first part of the query (count the idle instances between
an ON and OFF),

SELECT IdleCount.ct
FROM (
SELECT COUNT(NSEW) AS ct
FROM INBOUND AS Q1
WHERE DATEDIFF(DAY,Q1.DT,GETDATE())=7 AND Q1.NSEW = 'IDLE' AND Q1.VEHICLEID=137
AND Q1.DT >= (SELECT MAX(Q2.DT)
FROM INBOUND AS Q2
WHERE DATEDIFF(DAY,Q2.DT,GETDATE())=7 AND Q2.NSEW = 'IGNITION ON' AND Q2.VEHICLEID=137
AND Q2.DT < Q1.DT
)
AND Q1.DT <= (SELECT MIN(Q3.DT)
FROM INBOUND AS Q3
WHERE DATEDIFF(DAY,Q3.DT,GETDATE())=7 AND Q3.NSEW = 'IGNITION OFF' AND Q3.VEHICLEID=137
AND Q3.DT > Q1.DT
)
) IdleCount

however the results coming back are not what is expected, concluding that this sql statement is not right.

Do any guru's have any ideas?