Possible Clues:

• Cartier (anag.)
• Idle, broken by desert, becomes unstable
• One found in volcanic crater may be inconsistent
• Very unreliable chap who's a rodent catcher
• Having no certain course, Ernie's partner crossing desert
• Unreliable City, letting in one after endless delay from the back
• Irregular and unpredictable
• Irregular - eccentric
• Shifting like Cartier
• Ambler possibly catching rodent on irregular path