1988 s-10 blazer 2.8 , i put in a new iac valve with the gasket .the idle was higher than the origanal. 1500 rpm. i took it off and removed the washer to make it seat farther in .put back in and the idle went down to 1100 rpm . drove it up to 40 mph to reset iac. could it be something else. any suggestions would be helpful.