i have a 97 Z28, bone stock. 107,000 miles.

the car runs strong, has no problems at all.....exept.

at idle, when my foot is on the brake and the transmission is in drive it'll every so often have a small, small stumble.....and there's a whistling noise ONLY when it stumbles. it only stumbles/whistles about every 10 seconds, at first, and then it'll start getting worse and worse. like every 2 seconds.

if i put it in park it won't do it but maybe once every minute.

and it doesn't seem like it does it until the car warms up pretty good.

i put a new fuel filter on it, pcv valve, and cleaned my thottle body butterflies and the inside of the housing. that seemed to help a little bit, especially at first... i thought i had cured it completly, but it's still doing it.

i've heard LT1s have a rough idle sometimes, but i don't know about that whistling noise.

i'm going to replace the coil, wires, and plugs, just because they have over 100,000 miles and it could probably use it.

it runs like a scalded dog the rest of the RPMs, just idle.....and usually only when my foots on the brake and when it's in drive...

i don't think it's the brake booster, the whistling seems to be coming from further forward in the engine compartment.

i think it has something to do with putting that slight bit of load on the engine, it ALMOST sounds like a belt, but i sprayed the belt with dressing and the belt *looks* fine, but i'd think a squeaky belt would squek ALL the time. not just when the engine stumbles.

btw, the rpms only drop 50-100 rpms, not much at all.....

sorry for the long post, i searched every thing i could think and none of anyone elses problem with their car seems to be the same.

thanks for reading my really long post.

 

Besides Plugs and wires, which you are already taking care of, the only thing that I can think of is a dirty Idle Air Control valve (IAC) This is located on the bottom of the Throttle Body and can be removed with a torx head screwdriver. You can first attempt to clean it with a carb cleaner or you can replace it at any autozone. Hope this helps. I have an M6 so I have no idle problems (Never in gear when stopped )

Once again, Good Luck

 

that's probably it.

i would think if it was the plugs/wires it would do it throughout the RPM band.

i'll take it off tommorrow and clean it, hopefully that'll clear it up.
those are like 50 dollars at autozone....

thanks