1994 b4000 idle/rev issue

[Jothomo]

1994
Mazda b4000
4x4
216,xxx

No mechanical issues other than a leaky break hose and one I can't figure out, on occasion when stopped or on neutral the rpms jumps and the engine revs, like if the brake weren't depressed or it was out of gear it would lurch forward, like...vuh! Buhbuhbuhbuh vuh! Buhbuhbuh and so on. What causes this and how do I fix it

 

[RonD]

Does the Check Engine Light(CEL) work?
Comes on with key and then goes off.

If it is working I assume it is not on and there are no "codes" to check.

Could be an intermittent vacuum leak.
Leaking power brake booster.
Dirty PCV Valve
Leak in EVAP system would probably turn on CEL

Cleaning IAC valve and MAF sensor would be good general maintenance, not sure they could cause this issue but IAC valve could be getting sticky and computer can't hold idle steady.