[Bobo2001]

97 4.3 manual 2wd
High idle on start up to 3k and then settles after 2-3 seconds.
Idle stays up when switching gears and truck pulls itself with no throttle.
Putting truck in 5th and bogging it down to 1500 is the only way to get it down until a complete stop is made. Then it will drop after a few seconds. I hear what sounds like a vacuum leak when driving and trans is engaged but not while I’m under the hood trying to find it with my throttle body. Sounds almost like a blowoff valve when rpm reaches 3k and the throttle is released or changing gears.
Any advice would be helpful. I can’t seem to find it so far and I’m burning way to much gas driving around like this.

 

[944v8indfw]

On the 4.3's the throttle body sticking not closing all the way due to built up is pretty common. Pull the throttle body and clean well front and back with carb cleaner. Make sure to open the blade and clean the surface where the body and the blade meet. Might think about replacing the throttle body base gasket to be sure. You may have a vacuum leak as well. Visually inspect all the lines namely the big one the feeds the brake booster. You can also test with carb cleaner or even WD40 by spraying around vacuum line to see if idle changes. PCV line is another area.

Visual inspection would be first. Throttle body clean 2nd.

 

[Bobo2001]

Checked all vacuum lines. Replaced pcv valve and line elbow installed new throttle body gasket. I had already thoroughly cleaned the throttle body and replaced tps and iac valve. Still same issue.

is it possible my plenum is developed a crack or hole?

 

[944v8indfw]

Checked all vacuum lines. Replaced pcv valve and line elbow installed new throttle body gasket. I had already thoroughly cleaned the throttle body and replaced tps and iac valve. Still same issue.

is it possible my plenum is developed a crack or hole?

Could be idle air control valve sticking. You can unplug it see if it makes a difference. Possible plenum it could have crack or the oring / gasket sucked in. Should be easy to find with spray, even water is a squirt bottle.
When did the problem develop?

 

[944v8indfw]

Also possible you have a blow diaphragm in your brake booster. Easy check is unhook the line and plug it going to engine.

 

[Bobo2001]

Just recently began but the truck sat for about 6 months. Had some damage from a fender bender that I had to fix and didn’t have time so it sat until I did.

the idle air control valve is new. If it is sticking what would be the solution to that? Gonna try the booster as well.

it wouldn’t be the air intake gasket at the top of the throttle body would it? The truck has 180k and the gasket is there but I’m running out of places that the air could be getting in

 

[944v8indfw]

I believe on your year there is a vacuum reservoir in the drivers fender close to the abs system. Check it for a broken nipple or line namely after a wreck. It may also be a ball shaped on the hood or fender.

 

[Bobo2001]

I have the ball on the hood. It works fine and my HVAC controls work so that isn’t the source. Let me mess around some more and I’ll see what I come up with