It could be any of the following:

1. Bad ground to the engine (and hence to the starter)
2. Solenoid contacts are bad
3. Problem with the starter armature/coil (rare)

To isolate it, you need to wait until you have the problem consistently. Then...

1. Using a jumper cable, connect the negative wire from the battery -ve terminal directly to the starter body. Then try to start it via the ignition. If this corrects the problem, check the ground wire from the starter to the engine.

2.
- Turn the ignition key off and remove your key
- Put the car in PARK. DONT forget this step !
- Engage your hand-brake.
- Now inspect the starter. The solenoid-switch is mounted on top of your starter. You will see 1 fat red wire going to one terminal (attached with a large nut). This is the always-hot Positive conection (A) from the battery. Below that terminal you will find another similar terminal with a nut (B). The only wire attached to this one comes from the starter-motor.

- If you short A and B (you will need something thick like a stubby-screwdriver - as we're talking many amps here) the starter should turn. It will probably give you a heck of a start too :) AGAIN - MAKE SURE THE KEYS ARE OFF THE IGNITION, GEAR LEVER IS IN PARK AND THE HANDBRAKE ENGAGED BEFORE YOU TRY THIS ! This method totally bypasses the neutral-switch on your gear-shift, which means if your car is in gear and you try this, you could get run over. If your keys are in the ignition and switched on, the car could start too.

If this method causes the starter to crank immediately, but you still get a click when you try to start it via the ignition - then you likely have a problem with the contacts in your solenoid-switch.

Noel