I have a Camaro RS 1991 V8 TBI-Automatic Transmission, recently I started having strange problem. I can feel the engine vibrate while applying break and the shifter at D or R position (for example waiting at traffic light) and the rpm starts shaking and going below 900-rpm and as if the car will turn off. While driving the car I don't feel any thing. only at idl speed.
I replaced spark plugs but did not have any effects.
I only drive my car once every week and most of time kept in the garage.
Is it something to do with Fuel system or electrical system?
Thanks,

 

Check for vacuum leaks. Idle should be low, around 550rpms for a stock TBI 305 in gear.

 

Thanks for reply, in simple language (as I have fair knowledge) how to do that to locate the vacuum leaks? if something need to be replaced, what should I buy?

 

Check vacuum lines for cracks/breaks. Grab a can of brake cleaner and while engine is running, spray around intake and anywhere vacuum lines connect - if idle changes when sprayed, that's a leak. Brake cleaner less combustible and volatile than carb cleaner - but be careful with either!