Engine surges when in park

My 1992 Chevy truck started surging or reving up when in park. It will tac to 1000 rpm’s then go back down - up and down. It won’t barely drive down the road. Didn’t know if this is a fuel pump problem or something more serious. We’ve replace several parts that were described on the internet as “could be the problem”, but nothing has worked. HELP!

My first suspect would be a cracked or disconnected vacuum hose, so you might want to check into that possibility before you throw more expensive parts at it, at random.

If it turns out to not be vacuum hose-related, I think that diagnosis and repair by a good mechanic may turn out to be less expensive than DIY parts-throwing.

It would also be helpful to know what those parts were. The ones suggested by those internet sources.

But, yes. A vacuum leak would cause your surging problem and poor performance issues. Consider vacuum hoses, throttle body gaskets and intake manifold gaskets with your leak search.