Our '95 Z28 is having a loping/surging idle. It's a 100% stock car w/o any mods. I looked in the Haynes manual, and it said it could be the fuel pump, a leak in vacuum pressure from the intake manifold, bad EGR valve, bad PCV valve, etc.

I'm a bit dumbfounded as to what it could be because there aren't any service engine soon lights coming up on the dash. The dealership had it a week ago for the same issue, but all they did was change the fuel filter, thinking that was the problem. The fuel pump was last changed around ~01 or ~02.

Intake manifold has the typical slow leak from a bad OEM/original gasket. Do you think that's the cause? I'm hoping not, as that will be pricey.

My sister drives the car, so I haven't driven it other than starting it and hearing the unusual idle. I'm going to drive it today for a few miles though. She's said that is surges while accelerating too.

 

What 'typical slow leak from a bad OEM/gasket' are you talking about? The intake gaskets don't generally leak?

Take a look at the plugs. If they are the stock AC plugs, chances are that the little platinum pucks have fallen off giving you a really big gap and a crummy idle.

 

The plugs are new, from just a few months ago. I dropped the car off at the dealership myself earlier today and the car was driving like a brand new car the entire time. Don't know why it wouldn't lope at all. I stopped and started the car multiple times.

The time yesterday when I started it, the fuel pump gurgled at half ignition, the car didn't immediately start, and when it did start, I backed it out of the garage and it was loping the entire minute I had it running.