badbowtie03
Registered Member
Hey yall, is there a way to lower the idle speed of a tbi 350? I have an 87 K5. Just seems to high and really surges when you put it in gear. Thanks for any info!
CK5
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TBI high idle?
- Thread starter badbowtie03
- Start date
rampage
3/4 ton status
Spray around the throttle body intake gasket with carb cleaner and see if the rpm increases indicating the gasket is leaking - common issue.
Or a vacuum line or elbow has a crack you can also find them with the above mentioned method
badbowtie03
Registered Member
Great ideas! Thanks so much
I did a TBI conversion from carb and had the same issues. It was a vacuum leak that caused the same behavior.
There are a few places around the intake and throttle body that can have leaks. Be patient - hook an rpm gauge so you can see what’s going on while finding the leak like others have said. You’ll see the RPM change when you are spraying.
badbowtie03
Registered Member
I did just find a cracked and collapsed rubber hose. Not sure where its supposed to go exactly. I took a few pics. Rpm did go down when I closed it off. Anyone a pro at what all this stuff is and how its supposed to be routed? the elbow that comes off the intake is what was leaking... Just not sure where that hose is supposed to go. Its about 12” long? I then hooked it up to this diaphragm looking thing on the back right of the tbi. Im gonna go get some new hose... what is that diaphragm thing also? Also where is that white wire supposed to go coming off the coil?
The first pic I was just curious what the thing is with the orange hose on it...
2nd pic is me pointing at the elbow and the bad hose connected to it... where does that go?
3rd pic is broken white wire
4th pic is the diaphragm thing that i hooked the bad hose to. Is it supposed to to there? Im gonna get a new hose for that for sure.
The first pic I was just curious what the thing is with the orange hose on it...
2nd pic is me pointing at the elbow and the bad hose connected to it... where does that go?
3rd pic is broken white wire
4th pic is the diaphragm thing that i hooked the bad hose to. Is it supposed to to there? Im gonna get a new hose for that for sure.
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The last picture is cruise control and it looks like it is busted, I see a rivet off on one end of the bracket
badbowtie03
Registered Member
I was wondering if it was something like that. Yeah it definitely doesn’t work! Be nice if it did though...
Ist pic is egr valve, not sure why there is 2 vacuum diaphragm's...
2nd pic is manifold vacuum and mine is capped, but most likely the vacuum source for the cruise control.
3rd pic is the tachometer wire or coil negative, not used unless you have a tach/rpm guage.
4th pic is cruise control vacuum diaphram like mentioned above.
2nd pic is manifold vacuum and mine is capped, but most likely the vacuum source for the cruise control.
3rd pic is the tachometer wire or coil negative, not used unless you have a tach/rpm guage.
4th pic is cruise control vacuum diaphram like mentioned above.
badbowtie03
Registered Member
I will look closer at the diaphragms tomorrow. You think someone added a 2nd on there? Normally only 1?
My motor only has 1 diaphragm on the egr. Looks like a second one was added. Mine has the plastic vacuum line with rubber ends going from the egr solenoid straight to the egr valve bolted to the intake.
badbowtie03
Registered Member
Hey do yall know what this broken line is? Is that a vac line? Where should it go? Just trying to get this thing running as best it can.
Also I tried to take a better pic if these egr diaphragms... looks like this “2nd” one has a hose and connector down to the intake also. See the small orange one going toward the intake? Then the too orange line goes to the top of the permanent mounted diaphragm.... is this correct? I was Searching if I can remove all this crap but it looks like there are mixed reviews if it will mess with the computer or not?
Also I tried to take a better pic if these egr diaphragms... looks like this “2nd” one has a hose and connector down to the intake also. See the small orange one going toward the intake? Then the too orange line goes to the top of the permanent mounted diaphragm.... is this correct? I was Searching if I can remove all this crap but it looks like there are mixed reviews if it will mess with the computer or not?
The nylon vacuum line going into the firewall is probably for the A/C & Heat control,the "blend doors"and the flap that changes from heater to defroster in the heater box are operated by vacuum cans similar to those 2 on the engine...
Never seen 2 EGR vacuum cans like that before--might be some CA only emissions or something ,or else someone cobbed the second one on there for some reason..
Never seen 2 EGR vacuum cans like that before--might be some CA only emissions or something ,or else someone cobbed the second one on there for some reason..
badbowtie03
Registered Member
Do you know how its supposed to be hooked up? Is that nipple supposed to be plugged that the 2nd diaphragm is connected to or where is it supposed to run? Thanks
Sorry,no idea on that--I think the heater control vacuum line originally was hooked to a "vacuum ball" storage canister,that got manifold vacuum right off the intake manifold..
Poking around on google images I found this 1987 K10 vacuum diagram,but be aware there are many variations in how they were set up according to what state the vehicle was sold in and the diagram isn't showing all possibilities--this one fails to show the A/C vacuum ball and line going into the firewall,and only shows one EGR vacuum canister..
Poking around on google images I found this 1987 K10 vacuum diagram,but be aware there are many variations in how they were set up according to what state the vehicle was sold in and the diagram isn't showing all possibilities--this one fails to show the A/C vacuum ball and line going into the firewall,and only shows one EGR vacuum canister..
Here is a vacuum diagram of the HVAC/cruise control vacuum lines.
badbowtie03
Registered Member
So one thing that is helping slow the idle down is getting rid of the PCV valve. I am putting a breather on the valve cover and plugging the port on the TBI. Still seems just a little too high. I bought a tach to see what im really at... I will let yall know soon... also, where is this idle screw that I have read is “non adjustable”, but then i read people have adjusted it? Thanks yall
Getting rid of the PCV valve isn't a good idea,it'll let pressure build up in the crankcase and create sludge too--since it works off vacuum and is a controlled vacuum "leak" ,it affects the fuel mixture also, and if your engine idles slower with it blocked off,that proves you have air getting in the intake somehow...or maybe if it has an idle air control valve,that isn't functioning properly..
Stay away from the idle screw unless you have messed with other things like cam, exhaust, etc., or you are fixing the idle someone else messed with.
TBI's idle is not adjustable...it has a set parameter it tries to reach, and anything that is done to modify the engine leaves the engine trying to still reach that RPM. Which means more fuel to get the mixture right, closing the IAC to try and reduce the air to the engine, etc. The proper way to set TBI idle is called the "minimum air setting", but again, unless the engine/TBI has been monkeyed with, you don't need to do this.
It's programmed by GM to work with the PCV. Put it back, find the real problem. If you can shake the PCV and it clicks, it's fine. Or so I've read.
The screw as far as I remember is on the drivers side front of the TBI, behind a small plug.
badbowtie03
Registered Member
Well, im not gonna plug the valve cover. Just put a normal breather on it like any classic small/big block. Its how they ran forever right?
