Catalyzes the demethylation of isoprenylcysteine methylesters (By similarity). May be involved in the regulation of ABA signaling (By similarity). [protein]-C-terminal S-[(2E,6E)-farnesyl]-L-cysteine methyl ester + H2O = [protein]-C-terminal S-[(2E,6E)-farnesyl]-L-cysteine + H(+) + methanol Expressed in roots, rosette and cauline leaves, stems, flowers and siliques. Down-regulated by heat treatment. Belongs to the AB hydrolase superfamily. Isoprenylcysteine methylesterase family.