My idle has always been a bit high (1000 - 1300 RPM). But the last couple days it has gotten progessivly higher.

Yesterday while driving I noticed that I could let my foot off the gas and the car would maintain speed almost as if cruise was on. I looked down at the gauges and noticed my RPM'* (with foot off the gas) were hovering around 2K +/-. At the same time my boost gauge was reading around -5 PSI (5 psi too high for no throttle).

This morning on my way to work I noticed that if I let off the brake, while at a stop, the car would slowly start to accelerate (say 10 mph in the first 20 seconds). It wasn't just the fact that the car started move, but rather it was really slowly accelerating, and not just torque rolling. When I got to work I did my badge and the gate thingie, and then proceeded to go up a parking ramp. While going up the ramp, with my foot off the gas, I maintained 10 mph. This ramp was steep enough where I should have rolled to a stop quickly. Once I parked the car the idle climbed to about 1800 rpm. I tapped the gas to see if I could step it down. It just went up to about 2k rpm, so I did it again. Then it went up to about 2200 rpm. At that point I just shut the car off and went inside.

Other things I have noticed...

While driving yesterday I would let off the gas and the boost gauge would actually go from -7 PSI while lightly on the gas to about -5 psi once I pulled my foot off. about 20-30 seconds later it might drop back down to -10.

The car usually starts at the expected 1k rpm range. Only after I have been throttleing up the engine (such as driving) has this occured.

My thoughts are either I have a bad sensor somewhere or I may have a stuck throttle cable. Who knows, maybe even something with my boost is causing this (holding boost vs dumping it)? Any ideas where to start???????

i'd definitely check the throttle cable, similar thing happened on my uncle'* car and when I checked his throttle cable, some rubber or greasy mess had gotton on the throttle cable and was sorta keeping it from going back to normal position when he let go of the pedal. just a quick wipe down and some WD40 took care of it.
I don't have a supercharger on mine so i dont know where to start with looking into that but i don't think it would cause this.
Also, this isn't too likely but just to get it out there, maybe its something with your Idle Air Control valve? could be getting stuck? But if it were then I would imagine it would be high right from the start which you said wasn't happening.

This is also doubtful but just to let you get another idea: Maybe your cruise control is holding its vacuum?

I guess one thing you should try doing is: when it happens again, feel your gas pedal and see if you can tell if it'* actually being held down some by some unknown force (stuck cable or cruise control sucking it in place?). If it isn't being held down at all, then you should at least be able to rule out a few things.

Good luck!

Michael Diaz
'87 Pontiac Bonneville
K&N Cone.. that'* about it