I recently changed the plugs, wires, cap and rotor on my Trans Am and now the Tach is not working right when I start the car the needle bounces between 1100 and 1400 RPMS for a few seconds before dropping down to 0. It bounxes up a couple of times to around 200-300 then falls back to 0 and stays there.

I used the following parts:
AC Delco spark plugs (same as what were already installed)
MSD Street Fire plug wires
MSD 8406 cap and rotor

Also the ignition control module was replaced in January with an AC Delco unit. I believe the ignition coil is only a year or two old

Any suggestions or ideas on what i should check? The tach was working fine before this.

 

Okay so I ran the car again tonight for the first time in a couple of days. The needle bounced between 1100-1500 RPMS but it lasted for a few minutes. I revved the engine a few times and the tach responded but it seemed to lag a bit. But as the engine warmed up the readings dropped to between 700-900RPMS. At this point the needle didn't respond when revving the engine and it finally dropped to zero.