The mechanical bits in this devise get stuck sometimes. Remove the rubber connector pipe and spray in some WD40. Works for me when the idle mechanism gets cranky.

__________________
Berfinroy in CT
Present vehicles:
1973 300 SEL 4.5
1959 Rolls Royce Silver Cloud I
1959 Ford Thunderbird convertible/430
Past vehicles;
1958 Bentley S 1
1976 ex-Max Hoffman 6.9
1970 300SEL 2.8
1958 Jaguar MK IX
1961 Jaguar MK IX
1963 Jaguar E-type factory special roadster
1948 Plymouth woody
1955 Morgan plus 4
1966 Shelby GT350H Mustang