I have been trying to get to the bottom of this problem for a while now and I seem to be getting nowhere. First things first, my tachometer isn't calibrated correctly so I cant really give any RPMs. Okay, sometimes when I turn on my car it idles very high. Other times it idles just fine when it feels like being my friend. But when I drive this seems to happen all the time at some point or another ... once I press down on the clutch the RPMs will shoot up. The RPMs will still stay high when I am in gear (but not as high as if I was in neutral) and manually revving the engine used to work as a temporary fix, but its not working any longer it seems.

I have already cleaned the IAC valve, replaced the TPS, replaced the throttle linkage cable, and cleaned any and all dirt and gunk sitting on the throttle body and springs. I also did the paperclip code-reader thing and no codes came up for me. Is there anything anyone here can suggest to help my problem? I would hate to have to take it into a shop since I prefer working on it myself

The engine is a TBI 5.0L Chevy 305.

 

Have you done any mods like open air cleaner and not put the air temp sensro in it? Or the ****-E-bay performance chip that plugs into that temp sensors socket? Or anything at all?

 

Nope. This car is stock, no mods.

 

take a spray bottle and some soapy water, spray all the vacuum line, im sure you have a leak somewhere

 

I just was trying to diagnose the problem again and I think I came across something useful (at least I hope). First of all my PCV filter is dirty and needs to be replaced. I also noticed some wet gunk sitting at the bottom of the filter housing. So I will be replacing the filter, but the suction on the hose seemed to be okay. However, after paying closer attention I noticed a hissing (sucking) sound when the engine is running and I can hear it clearly for half a second after I turn off the engine. I couldn't pinpoint the exact area where it was coming from. I also noticed that the hose on the PCV valve could have been tighter which may be where the hiss was coming from but i couldnt feel any suction there when I felt with my fingers. Any thoughts on this guys?

 

again, check ALL your vacuum lines and ****. if that doesnt turn anything up, hook up your code reader. and about the pcv, your might as well replace it they are cheap.

 

Just because you cleaned the Idle Control Valve, still doesn't mean that it's good.
It's electrically controlled and acts as a plunger that opens to allow more air into the TBI when the engine is cold. After warm up, the plunger closes off the inlet port and slows down the idle. It's still possible that it isn't working, and not closing off like it should.
On FI throttle bodies, there is an inlet hole (or slot) near the intake that you can hold your finger over. If the idle slows down, you know the IAC isn't working. I don't know of a simple test like that for the TBI. But since your idle is funky, the Idle Control Valve would be my next logical "guess".
Idle Control Valve

 

here's an odd question but how do your brakes feel? if the supply line to the booster comes off it will revv the engin, and hiss alot :P check that too.

 

Lithorian
I actually just replaced all of my brake system (pads, caliper, rotor, hose) and bled the system and the brakes have never been better, but I still had the problem. (I fixed it for another problem FYI)

Camaro 69
I am thinking the IAC is fine. I noticed that I have a coolant leak which I believe to be contributing to it. I noticed it leaking from the hose that enters the engine at the front middle and its also leaking through the RTV gasket. When the reservoir gets low it seems to rev higher. I plan on fixing it when I get a chance to.

 

I think Lith was refering to the vacuum line that goes to the brake booster itself. since you heard the hissing, I am betting you have a vacuum leak somewere and need to find and plug it. I know little of the injection systems so keep in mind what camaro 69 mentioned as well.