my WDT program is working fine in normal mode, but I get a time out from the wdt if I include in my program
PCON |= 0x01; // idle mode

You may not intend to, but you are using the WDT as "periodic wake-up" a specified feature of the LPC9xx.

If you look at table 4-2 in the user guide you will see that WD has "yes" in the Power down wakeup column.

Erik