On a 2001 B18 with a jg edelbrock throttlebody, we replace the stock throttlebody with a 68 mm holley throttlebody. Now, the check light is on and it idles to 3000. It was working normally before we replaced the throttlebody. All connections were double checked. Any ideas? Thanks.

 

MAP Sensor? TPS? idle screw? these are all the items I would check.

 

When we put back the old throttle body, everything is back to normal.

 

Sounds like a vacuum leak, try a ITR TB Gasket.

 

3 things come to mind.did the new throttle body come with a tps or did you have to swap?if swapped,it has to be adjusted correctly.a vacuum leak is possible.try spraying around the base with carb cleaner to see if idle changes.make sure air adjustment screw on the body is not adjusted to far out.i have come across bad
butterfly shaft bearing problems on some upgraded throttlebodys.hope this helps.