Chevrolet Repair: 92 Chevy PUp (TBI) Erratic Idle on warming, hesitation, throttle position sensor, vacuum leaks

Question
I have a 92 chevy pickup with a V-6, 4.3L 262 cu.in. engine. w/automatic and air cond.  I am experiencing an erratic idle on/off usually with a warm engine and more pronounced with the brakes on in drive or reverse.  I have checked the EGR valve and even disconnected/plugged the vacuum line and it still has the erratic idle on/off.  I am checking it with the air cond. OFF.  This engine has TBI system and I have put 2-3 bottles of fuel injector cleaner in the gas tank as I first suspected bad gas/water in the tank.  Can you advise me what else to check, could it possibly be the TBI fuel injectors,throttle positioner sensor and/or the O2 Sensor?  The engine is experiencing a little hestitation on takeoff as well.  How can I test/check the fuel injectors as this engine has 190,000 miles on it.  Otherwise the engine runs fine and idles at times like a kitten, real smooth. I did check for hose vacuum leaks and the power brake booster as well and didn't find any,as it tends to start when the brakes are applied. Please email/post as soon as possible as I need help !
Thanks,
Kenny

Answer
Hello Kenny,
Vacuum leaks is what it sounds like, but sounds like you are doing a good job of checking that.
The EGR valve, if it opens, and then seats on some carbon, would be a big vacuum leak. You said you unhooked the vacuum line from it. I didn't understand though if you left it unhooked for a while, and still had the on/off idle problem, which should eliminate it if you did.

A vacuum gauge connected and observed during the problem would be nice, as well as a fuel pressure tester.

The throttle position sensor could defanitely cause that, and can be checked with an ohm meter.
Since it only happens after warm up, it would point toward an electronic item, like a sensor, since they are not used until after warm up.
A low fuel pressure or vacuum leak could happen before warm up, except for the egr valve opening.

There is the possibility of a loose connection also.

An O2 sensor, if dirty, should cause the problem every time after warm up, unless it has the loose connection, in which cas it should store a fault code and turn on the engine light.

If the hesitation is there all the time, I would concentrate on the fuel pressure, and the TPS, both of which can be out of spec and not store a code.

Van