Understandably a great deal of time as past since this was posed ... but I came across it in Apr of 2013.
In case anyone else experienced a similar mystery of their RX not starting after taking off the rear valve cover & doing any work / tune up on the back of the motor. I had done just this and my RX WOULD NOT START. It would crank, and crank but never 'catch' & run. After reassembling it, I tried multiple tests and finally committed to taking it apart again and sift thru the wiring harness to see if I stressed or damaged any of them during my work.
After taking off the wiper assembly, and after removing the intake manifold for the second time - I noticed what turned out to be the problem in my case. When I removing the "blind" bolts from the back of the manifold and removed it; I saw my mistake. ONE of the two ignition grounding wire pairs had gotten jockied around during disassembly and went unnoticed when I reconnected the bolt thru the wire crimp washer. I only reattached one pair of wires rather than finding and securing the second pair. Without that second one being grounded the engine would crank and crank but never fire and run.
Being 6'7" tall with sausage fatigued swollen hands made it really tough to reach and access the bolts between the back of the engine and the firewall on this car. WAY too tight of an engine fit IMO. I'll gladly work on my Toyota LandCruiser any day of the week over this thing. The LC you can practically sit on the fender with you feet in the engine bay and still have ample room to work. It is the polar opposite of the RX300.
