[allinallcamaro]

90 IROC-Z 305 TPI. Every time I pull up to a red light and start to idle at around 900RPM the car has one little shake drops to about 600RPM then back up to 900 again like every five seconds . I figured it was the timing belt but its not and I checked comppersion, checked fuel pressure, did everything I could think of even cleaned the cat out.
3.73 rear end
High performance cam (Is idle time to low)
K&N air filter
High comp head
Performance chip
(only upgrades made)

[ZZ430DropTop67RS]

Try cleaning the throttle body, IAC pintle and passage.

[Mike's67]

Does it do this with the a/c off?

[allinallcamaro]

The ac is off.

[wplax26]

Fuel filter?

[TRT]

Possibly EGR valve sticking