88 chev. g20 van idle problem

I have a '93 5.7L(K) TBI engine with a turbo 400 trans in my van with a 3.73 posi rear. the problem is that about a year ago the engine would stall out when i put into reverse.Now it does it in forward, also! I have to keep foot on gas pedal a little bit while braking to a stop or the engine will stall out. It idles fine when in p and n, only when it is in gear it stalls.No vaccume leaks any where on engine or rest of the van. At idle in park, i could hear whistle at front of throttle body,wiggled vaccume lines around and found sound to be coming from vaccume port for egr valve electronic unit.I pulled hose off port and whistle went away and then put finger over port and whistle came back.I then removed tbi and cleaned it and installed a new iac(idle air control valve), then reinstalled tbi.whistle is still there and still stalls in gear.The whistle comes and goes!Fuel and electric systems are all ok!No check engine light on and no codes set when scanned with snap-on scanner.With engine running in park with scanner plugged in ,real time values are within limits,bad tork convertor maybe?

Plug vacumn port to egr valve and see if that helps.

Make sure your have a good PCV valve.
And no vacumn leaks.

Is the PCM controlling IAC valve.

Does the IAC counts go up when put in gear or ac turned on?
What are the IAC valve counts reading?

I would also replace the TBI body base gasket and clean vacumn ports in the base of it.

hi mt2500,as i said in my post as stated,i cleaned all ports on throttle body,replaced iac,no vaccume leaks,replaced tbi base gasket,real time operateing values are ok with scanner,no codes set,engine runs smooth at idle in park,with engine idleing in park tested egr valve by pulling up on diaphram,tested ok,,engine rpm died down like it is supposed too,,ok,,removed vaccume hose at egr port on throttle body,no whistle,plugged port with finger and hear a whistle. First, let me tell you that i'm a 42 year exp. auto tech and never incountered this problem before,,i'm stumped,,could there be a problem with the throttle body?And, or is the tork convertor bad that it is locking up (rpm stall) with trans? Like i said, it all started when put into reverse and later happened in forward gears! need more input,more heads are better than one!

To test for converter lock up jack all drive wheels and put it in gear.
let us know if it still kills motor that way.

I would suspect the pcm is not controling the IAC valve or IAC valve is bad.

Does the IAC count raise up when put in gear or ac turned on?
What is the iac count reading out of gear and in gear?

Unplug IAC valve while engine is running in gear if you can.
Then Pull IAC valve and see if plumger is retracted most of the way.
With valve out plug it back in and turn key on and see if plunger goes out.
Letus know how all of that goes.
Gooed luck

On the egr valve line whistle plug it for testing.
Can you find where the whistle is at?
That may be a problem area.

Plug the PCV valve also and check for whistle there.

hi mt2500, will get back to you in a couple of days on your suggestions.Experancing an ice storm here in PA. right now and vehicle is outside, will get back to you on my findings as soon as possible..thanks!

mt2500, by the way,forgot to tell you that the new iac(idle air control valve) that i replaced is working fine,cold start up, rpm's are high as normal, engine warmed up,rpm's drop down to normal, snap-on scanner in real operateing time values are fine with no codes set! but engine still stalls when put into gear with foot on brake. Like i said before,,problem first started when put into reverse(stalling), never in forward gears. Then months later, it started to stall when put into forward gears.

mt2500, by the way,forgot to tell you that the new iac(idle air control valve) that i replaced is working fine,cold start up, rpm's are high as normal, engine warmed up,rpm's drop down to normal, snap-on scanner in real operateing time values are fine with no codes set! but engine still stalls when put into gear with foot on brake. Like i said before,,problem first started when put into reverse(stalling), never in forward gears. Then months later, it started to stall when put into forward gears.

You are welcome.
If IAC valve woring good could be in transmission lockup.
Are you getting a stall when braking to stop or acting like a standard transmission when stopping without clutching?
Or does stepping on brake change engine idle?
If so make sure brake booster is not losing vacumn.
Does it stall if put in gear no brake on or with all drive wheel off ground no brake on.
Or driving and stopping with brake on does engiune pull down and or stall?

let us know how it goes.
A ft. of snow and blowing hard here and still snowing in N. E. Missouri mark Twain land.

mt2500, yes, it stalls when coming to a stop with foot on brake pedal. To prevent engine from stalling i can either put gear shifter in n or keep foot on gas pedal a little bit to keep rpm's from dropping and stalling out. plus, when i leave off the brake and give it gas to go, it drives fine, shifts normally,slowing down,,down shifts normally,,but just keeps stalling at a complete stop,,like it(tork convertor)won't unlock to go into nuetral at a stop.

mt2500, yes, it stalls when coming to a stop with foot on brake pedal. To prevent engine from stalling i can either put gear shifter in n or keep foot on gas pedal a little bit to keep rpm's from dropping and stalling out. plus, when i leave off the brake and give it gas to go, it drives fine, shifts normally,slowing down,,down shifts normally,,but just keeps stalling at a complete stop,,like it(tork convertor)won't unlock to go into nuetral at a stop.

That does sound like lock up clutch draging or sticking soenoid.
If sticking on all the way it will pull engine down and kill it at a complet stop in gear with brake on.

Can you feel the lockup clutch come on in higher gear and unlock when you step on brake a little going down the road steady?
Does your scanner give any transmission lock up data.
The break light switch should break the circuit to lockup clutch and turn solenoid off when brake pedal is pressed?
Is break lights working good?

Just trying to give you ideas and things to check.
Hope they help.
Good Luck

hi mt2500, first off i'd like to say that this trans is a turbo 400(no electric commands from the computer)full fluid operation. As to the brake light switch, it has nothing to do with the trans, the only electrics connected to trans is nuetral safty switch at shift lever on trans shaft. I can rebuild stanard trans, but never ventured into automatics(there i would be lost). this is why i'm here to find out if i got a bad trans or tork convertor or both, or if there is something wrong with the throttle body it self, because of the whistle noise coming from the egr port on throttle body.