90 3.1 high and low idle problems

[stockgp]

first, the car is a 90 grand prix ste 3.1 5 speed.

the problem is when i push in the clutch to shift gears or when i'm coasting to a stop, the idle is up around 2500. when i come to a complete stop, the idle will return to around 1100, or occasionally 800-900. also, when the idle drops to 800-900 range, it's very rough. anything above 1000rpm and everything is smooth as silk. oh, and if i'm sitting at a red light too long, the idle will slowly creep back up to around 2500. kind of like a carbureted car when it's loading up. if i tap the gas, idle drops down to normal.

last thing, how high should oil pressure be on the 3.1? my check gauges light is almost always on, and the only gauge that looks like there could be a problem is the oil pressure. it's always at 3/4 or over the max pressure mark. i think it's probably just fubar, but who knows.

new ac delco wires, rapidfire plugs, and 02 sensor within the past 50 miles.

i'm thinking it's a vacuum leak, because my cruise doesn't work and my hvac doesn't work. i'm probably going to do the 3100 intake swap. has anyone done a write up on routing the new vacuum lines and everything?

i've tried searching, but every time i click the link on this site, firefox closes...

so yeah, any help is greatly appreciated

[SappySE107]

Something is wrong. Could be a bad IAC but a scanner would be the fastest way to diagnose or at least start rulling out ideas. Im not sure how they idle in neutral while coasting down but 1000 idle RPM is way high. Should be 700ish. Don't trust an analog tach though cause 1000 could be 700. It shouldn't be rough though either with a bone stock 3.1 at that RPM.

[stockgp]

it's definitely higher than 700. i can hear that much. and it's definitely rough when the tach says it's around 800. of course, it is analog, so you could be right baout it being off.

as far as getting the car scanned...i really don't have time. i pretty much work 7am to 7 pm every day except sunday