Fast idle sometimes, normal idle sometimes. 2001 Chev Venture 3.4. engine runs fast enough to hold 50mph with throttle closed. Cruise control is disconnected as I thought it might be that. What's wrong?

By "too fast", do you mean VERY fast? Does idle speed drop when you turn off the air conditioner? Generally, any sensor malfunction will trigger a code... but not always.

Check the cruise control cable - be sure it's not binding or otherwise pulling the throttle open.

dont drive it. find the cause and fix it now.
Hot and cold engine or BOTH>?
1995 Tracker, no tranny , no 4wd , on engine options stated.
Exact high RPM in neutral, not stated...... 1500 is normal cold.
keeps going in Neutral. (nah , you have 5 ways to stop any car.
key, hand brake, foot brake and neutral. and with 4wd, 1 more neutral.
keep that in mind driving any car.
this car has up to 3 throttle cables that can stick. and more!

1: floor mats hit the pedal>? ala. Toyota style (lawsuits)
2: the three cables are, throttle. , cruise and A/T transmission kick down cable. if car is M/T and no cruise it has 1 cable.
so disconnect it, throttle fixed? (disconn,. 1 by 1, bingo?

no cure?, then its not the pedal , you meant just high idle.
yes, replace the cable or bad parts three.
ok say its not the cables.. (tests proved that)
the 95 came with 2 engines, 8valves and 16valves,
they work differently (8v love so race, 16v loves to stall)

1: ISC Stuck open, common.
2: 8v, any air leaks at all , will cause super high idle speeds.
3: throttle valve in the throttle body is stuckopen (gunk) or the return spring broken (very very rare the latter,in fact never heard of one breaking)
4: IAC (thermal idle control stuck open ,(my 97 was). and lots more.
5: on the 16v it takes 2 failures. to make high idle.
gross rich running engine (cold engine its normal) and any air leak
once hot the engine can not race unless there is huge overfueling
and an air leak.
6: the 8v has this device on the side of the throttle body.
called a dash pot. its just a fast idle vacuum servo.
if stuck open the engine will scream full time....
7: ECU stuck in limphome, can cause too high idle speeds.

we need to know which engine
http://www.fixkick.com/find-parts.html
8v or 16v first.
then does the idle race hot or cold or both (engine temperatures)
if it races , then how fast?, RPM the dash tachometer tells you that.

it can be as simple as a 50cent hose cracked.
to a dead ISC. (idle speed control) IAC is thermal idle air controller.
the IAC must be closed on a hot engine,
if the the engine never gets hot,it will scream full time.

Can't adj..clean your IAC. Idle Air Control valve, or possibly replace it. The Computer adj's you idle by this valve moving in and out, it gets carboned up and does'nt move like it should.

The problem that you describe is in no way normal. That six second lag that you describe is more than enough time to get you into a serious accident. I have experienced a similar issue on Mitsubishi automobiles. When the hold down on the throttle cable is holding the cable too tight (not enough slack in the cable) or if someone has adjusted the throttle cable to remove the slack causing it to be too tight it will cause a fast idle lag like you describe. On several fuel injected cars stick and automatic I have experienced the engine rev issue you describe. Every time it was fixed by setting the cable tension back too loose.
Another item, if the cable slack does not fix the problem, fuel injected cars are fitted with an Idle Air Control Valve (IACV). They are located on or by the intake throttle valve. The price range for most is $30 to $100. If they malfunction they will raise the idle speed by letting too much air go around the throttle valve raising the engine speed even though the valve is closed. You can check if the throttle cable is too tight yourself. The IACV may have to be checked at the dealer. Only the dealer can tell you if the problem is covered under warranty.
As always check to make sure that there are no loose vacuum lines under the hood.

Check for anything that may be against your throttle cable. Look from the throttle body and follow it to the firewall. Your throttle body (butterfly could be staying open) The throttle body may need to be cleaned, once these get gunk built up, the butterfly will not close completely. If it can't go to a close state, the it's like having your foot on the gas pedal a little. The cleaner can be purchase at a local auto store. (throttle body cleaner)

thats it may be the fuel pump, and the reason why its worse when cold its becouse, when you start the engine cold it needs more fuel to function properly and hold a good idle until it gets its normal operating temp, during these moment the ecu increases the injectors pulse duration to get more fuel to the engine and perhaps a low fuel pressure will give bad fuel atomization and it gives you bad idle and cruise quality, I recomend you to check your fuel pressure for abnormal readings it can be easy by the injectors fuel rail, i hope it help's good luck

check the idle control valve they sometimes get dirty

the idle air control valve is stuck,or there is a vacuum leak.check the vacuum lines,the throttle cable is not sticking and the idle control valve which is on the side of the throttle body and the throttle position sensor.check all the plugs on these for a good connection.

idle air control valve defect or egr valve stay open clean throttle body with air intake cleaner sometime its a bit hard to start after its normal and for egr valve gently tape it hope it help you fixya our post thanks pierre

Cruise control has nothing to do with it, your pick-up is malfunctioning, it is located below the distributor or the coil pack. Replace it ASAP