1986 Sierra Classic Wont Idle!!

[domino33]

4.3 v6 quadrajet m4med

Cannot get truck to idle after taking off and cleaning carburetor. Choke is working g properly and truck idled (high) while running on choke (after messing with choke idle screw). Once warm it will not idle. Have tried backing in and out idle adjustment screw on drivers side (after it was at operating temp) but still wouldn't idle. BARELY have to have foot on gas though.. no vac leaks that I can see..everything hooked up as it was..truck idled fine before I took off carb. Replaced base gasket with one from advance...didn't look exactly like old one but fit correctly..didn't cover entire underside of carb but fit perfectly around the holes and profile of the carb facing out (front, if carb was on engine) like I said it fit pretty much and was 'specific' for my vehicle (4.3)


The idle mixture screws are currently each two and a half turns out.. egr isn't and wasn't hooked up. Capped it off. Bad fuel pump? Took carb off because when I went to tune it the outside was so.dirty I decided to take it off and clean..before I took it off I think it was rumming rich. Have found too much contradictory information so I'm posting here with as much detail to my specific problem as possible. God forbid anyone around where I live know how help me out.....thanks

 

[89Suburban]

What about the idle adjustment screw?

 

[HotRodPC]

Sooooooooo about this EGR that wasn't hooked up and working and capped off. So are you saying you just now took the EGR off and blocked it off? If so, put the EGR back on and see what happens. I have a feeling you may have an internal vac leak. If that was done previously and it's been fine, then leave it alone as is.

I'd be suspecting the base gasket as the problem. I've seen it happen a few times. One little orfice being blocked off or something NOT being blocked off will do it.

 

[domino33]

I attempted to adjust the idle mixture screw, turning it both in and out. It seemed to make little to no difference (as I said, truck was warm when I did this). At the moment the screw is in a fair amount.

As for the egr, it was never hooked up, just for clarity though, what port on the carb should it be connected to? Going to snap some pics when I have a chance...
Currently thinking the base gasket too..as that is literally the only change I made once reinstalling the carb. Truck should at least hold an idle even if the air/fuel screws are a little off, right?

Could timing be retarded?
A bit lost, a bit irritated. Thanks for the responses, gonna order another gasket that is shaped EXACTLY like old one...so that will be a few days until it gets here. Any other suggestions would he helpful!!

 

[Chaz]

Put the old gasket back on if its not torn or damaged???

 

[domino33]

It was so brittle that it broke in half as soon as I picked it up off the manifold. Wishing now that I didn't toss it though just for reference.
Read somewhere that one guy simply didn't have his bolts tightened enough. He's like ''tightened them a half turn more each and no problem" could it be so simple? I have always been told to make sure not to crank them down too much.

Basically gonna tighten it a little more and if that doesn't work I guess carb is gonna come back off

 

[HotRodPC]

Doesn't really matter on the EGR if it was hooked up or not. If it was plugging off an orifice in the intake, and now you took it out, then that orfice is not un blocked and can create a vac leak. EGR is usually closed off at idle for this reason. It all depends on which type intake you have. Some you can use a block off plate, some you have to keep the EGR in place hooked up or not.

 

[Skweegle89]

Take some WD40 and spray it around the carb base while it's running. If you get an RPM change, it's leaking. Just don't spray it near the top of the carb. Don't torque it down too much. Aluminum threads can only take so much. Triple check that all of your vacuum ports are either used or plugged.


Sent from an old rotary telephone.

 

[domino33]

The egr remains on the intake. It has two bolts that hold it in place right under the carb. There are definitely no ports or anything on the carb that isn't hooked up. That's why I was interested in where the egr port would go to on the carb because every port on carb is hooked up to something so where could it have went originally? Understand its not really important but anything small I can do to improve it is a plus.

So have someone on the gas just enough to keep it running and spray base of carb? Will it idle higher or what?

 

[Skweegle89]

No don't get anyone to hold the gas. They won't hold it steady enough. Screw in the idle screw on the carb until it idles


Sent from an old rotary telephone.

 

[Chaz]

If theres no vacuum leak then there will be no change in idle,,,if the engine speeds up when you spray then you got a vacuum leak there

 

[domino33]

okay. so I got truck to idle by turning idle screw way in... didnt sound bad. got out and prayed wd 40 along the base, definite change in idle, but it slowed idle.

Im sure this means regardless that there is a vac leak there. also i have had my air cleaner off pretty much the whole time, i know it makes a difference, but when it comes to idle and things it shouldnt play much of a role, right?

also would like to note that there is a green wire with an orange plug that comes out of the firewall from the cab right about the wheel well, drivers side, that isnt plugged to anything? cant find anything it would go to

 

[Skweegle89]

okay. so I got truck to idle by turning idle screw way in... didnt sound bad. got out and prayed wd 40 along the base, definite change in idle, but it slowed idle.

Im sure this means regardless that there is a vac leak there. also i have had my air cleaner off pretty much the whole time, i know it makes a difference, but when it comes to idle and things it shouldnt play much of a role, right?

You have a vac leak under the carb. No big deal. You can try to tighten the bolts a bit and see if that helps. If not, take it off and go buy a good thick gasket.


Sent from an old rotary telephone.

 

[domino33]

okay man thanks. tried tightening, helped a bit but not entirely. I think i ended up with wrong base gasket somehow..just ordered another and it looks a little different.

one on there now is the left, one i just ordered is on the right. thanks for all the help

 

[Skweegle89]

The second pic is the correct gasket. They should both work, but I have had better luck out of the open center type like that.


Sent from an old rotary telephone.