blyth18md

typical morning...

I start the car in the morning, and it idles about 1200-1300 rpm on the fast idle.

After a few i tap the gas and she idles down to about 1000 and put it in gear and she'll drop down a bit more.

But after i drive it to school only about a mile, maybe two, and put it back in park she ocassionally (about every other day) will go up to about 1500 rpm and stay there, if i tap the gas she wont come back down.

Turning the car off at 1500 rpm sometimes causes a little dieseling.

I also not too long ago finally got my headers and new exhaust on and i havent had time to schedule an appointment to get an o2 sensor bung put in.

Could the issue lay in me not running an O2 sensor? Could it be me just not giving the car enough time to get up to temperature with such a short trip?

naf

iTrader: (7)

Sounds like a vaccuum leak. When it's idling high pinch all your vaccuum lines with pliers and see if there's a change in idle. Could be a line that opens on a thermal switch.

The missing O2 sensor shouldn't cause this but it will run crappy without one.

five7kid

iTrader: (14)

On a short trip, the computer will be in open loop, so no O2 sensor wouldn't be an issue. That has nothing directly to do with idle speed, anyway. If it is trying to go to closed loop and you don't have an O2 sensor, you should get an SES light.

On a short trip, your choke may not be opening up all the way. More likely, though, your choke is sticking a little, so I'd suggest a can of spray carb cleaner for the linkages as a 1st step. Also, make sure the choke power wire is connected properly. It could have been disturbed during the header install.

blyth18md

might just be the choke wire..the choke light did pop on once...and i had to disconnect it when i was changinng the valve cover gaskets.

will check that out.

blyth18md

Ok, i cleaned the terminal and reattached the wire to the carb.

What should voltage be at the choke wire and at what key position should i check it?

Any other choke diagnosis would be appreciated.

five7kid

iTrader: (14)

Should be 12 volts with the engine running. It won't get voltage until the alternator voltage is higher than battery voltage.

blyth18md

what is the (short) vacuum line from the "t" to the passenger side of the carb? What is the piece called it is connected to?..would that line leaking give me any issues? The hose looks a bit too short, as in it seems to not be fully seated onto the "t's"

What would be the symptoms if it does leak?

Is their anyway i could cap it off for diagnosis to assure that i dont have a leak there(before i go ahead and replaceit)? All other vacuum sources seem to either be capped off well or have good hose, that one looks like it might be a tad short not created a good seal.


Sorry to be so long-winded, but id like to have a few possibilities to exhaust be for i go troubleshooting.

five7kid

iTrader: (14)

Choke pull-off, vacuum break, choke take-off. It's called all of those things. Its function is to open the choke butterfly slightly after starting to keep from over-choking the engine while running. The choke thermostat opens the butterfly as the engine warms up.

If it was leaking, it might not be opening the choke quite far enough after first starting, and might cause a slightly lean condition.

naf

iTrader: (7)

You can check the choke pull off itself for a leak by removing the hose, pushing in the plunger and covering the vaccuum opening before releasing the plunger. The plunger shouldn't move back out until you remove your finger from the nipple. If you're concerned about the hose, pick up some at a parts store and replace it.

Make sure the open end of the tee is capped. It normally connects to a vaccuum line that is part of the air cleaner. You can put a plug on it while the air cleaner is off.

blyth18md

Yes the other part of the t is capped off. I'll check to see if the plunger is operately correctly when I go measure the choke voltage.

blyth18md

The electric choke has power, charging voltage 14.3 or so.

The little vacuum break is holding fine with my finger over it.

What else can i check?

The choke should close completely once the engine is cool and I blip the throttle, right? How long should it take to cool off? I just had it running to check the voltage to the choke.

Park and Neutral are high and you can feel the car "load/unload" between a drive gear and not.

blyth18md

oops.

So I went back out to take a look around for vacuum leaks or anything i haven't notice so far....

Well on the back of the intake theres a fitting with 2 vacuum hoses( Im assuming 2 hoses as one was capped off).

I followed the one to a cylinder shaped object mounted above the brake booster and the fitting where the line attachs to this object was brittle and just fell off. What is this thing mounted above the brake booster attached to the firewall?

blyth18md

Ok so i dug through my manuals and finally saw a picture of what i was talking about its a vacuum tank for the A/C...i didnt see it mentioned in the heating section, is this tank used at all. I would like to keep the heat, but i have already removed most of the other A/C items, can i remove this and just cap the lines?

five7kid

iTrader: (14)

It's a resevior to keep the heat routing and cruise control operating properly in low vacuum conditions, such as going up hills. Without it, your heater/vent would probably go to defrost in those conditions, for instance.

blyth18md

We'll I dont have cruise anymore anyhow. So if i disconnect this I will only loose heat while pulling a hill or under heavy load, correct?

naf

iTrader: (7)

You can disconnect and cap it for now while you're troubleshooting but you'll probably want it connected later. It's the vaccuum line that comes off the manifold behind the carb, right?

Have we made any improvements yet?

zimmchile7

If the carb is a quadrajet, sometimes the throttle plate bushings wallow out check to see if you can pull the throttle arm back by hand when it is idleing high. If you can bring it back to a normal idle by turning the acclerator linkage by hand at the carb then that is probably your propblem. there is a bushing kit for it out there but I don't know where to get it. I had the same problem with mine and I threw the carb out and got an edelbrock.

blyth18md

yeah the line on the manifold..but the piece on the canister broke off..not the hose.

naf

iTrader: (7)

Go ahead and plug the line for now with a golf tee or a small screw. You'll want to replace the canister, probably check around at a JY for one.

blyth18md

I capped the line off...shes still idling retardedly high. What exactly should idle be in park/neutral vs other gears?

Ima go back to huntin for vac leaks

naf

iTrader: (7)

It should idle around 550-650 rpms in gear, about 600-700 in park. The guage tach may be off some.
1. Does the throttle stop rest on the idle adjustment screw?
2. Choke all the way open when engine warm (90 degrees)?
3. Did you give the choke linkage a good cleaning with carb cleaner? Nothing sticking?

blyth18md

1. throttle stop appears to be resting on the idle screw..kinda tough to tell with the taper on that screw..if its not on its really damn close

Would a weak spring get me close to the stop but not keep me on it completely?

Is the idle screw the only thing that limits the throttle or can you back the screw out so far that no matter how good the spring is it wont touch?

2.choke opens all the way.

Should the choke close completely when engine is cold or should it be just cracked?

3. choke linkage is clean nothing sticks and i gave it a good bath in carb/choke cleaner just in case.


I rechecked the brake booster isnt leaking vacuum I sprayed some carb cleaner around and didnt find any thing that would make it stumble.

naf

iTrader: (7)

A weak spring could keep it from resting. The choke fast idle cam will also keep it off the stop. Have you gotten any response from backing the idle screw out? Does it idle down when you push the throttle against the stop?

The throttle blades will limit travel back once they are seated. A bad or improper gasket or other internal restriction could possibly keep the blades from completely closing, but that is remote.

Choke should be partially open (cracked) when cold and gradually open as the choke coil is heated by the choke wire. If the choke were malfunctioning you'd be able to open it by hand when the engine is warm and blip the throttle to get the idle off the fast idle cam.

blyth18md

The throttle is so close to the stop (if it is indeed off) that pushing it against the screw causes no audible change in the RPM.

I'll try backing the screw out and see if it allows for me to push the throttle against the stop..if so I'll pick up a new spring i guess.

"It should idle around 550-650 rpms in gear, about 600-700 in park"

Mine goes from 1100-1000 to more like 750 in gear, keep in mind this is the factory gauge cluster tach.

blyth18md

was still idling high this morning..no luck as of yet.

tonight i purchased a new throttle return spring,feels a good bit stiffer, i'll check in tomarrow after school to let you know how it runs.

Any other ideas?

Throttle cable binding on something? I'll recheck and make sure the carpet isnt snagging, holding anything.

Still 1100 in park/ 750 in gear...im going to try to get the snap-on timing light/tach(while at school) on it to compare it to the dash tach.

naf

iTrader: (7)

Backing out the idle set screw made no difference?

Is 750/1100 an improvement on where we were before?

blyth18md

If the idle screw is backed off any more it wont make contact with the throttle stop anyhow.

750/1100 is where it seems to settle, sometimes it seems to hit 1500 and stay there until i shift in and out of gear or hit the throttle a few times.

blyth18md

The solenoid with the plunger, is just for A/C right? So i can remove that to have one less thing in the way while making adjustments, right?

A/C is long gone.

naf

iTrader: (7)

Yeah you can remove it.

blyth18md

New spring didnt help. Pedal feels nice now though

I pulled the carpet back to see if it was snagging the throttle/cable.... that didnt help any either.

I may go hunt around some more with the carb cleaner...but i spryaed it pretty good the last time and didnt get any response

MorbidHobo

I have the same problem you do as of right now except mine idels around 3000rpm (undriveable). Have you ever taken the carb or airhorn apart or messed around inside of it?

blyth18md

I personally havent taken apart, but it has been rebuilt. Which is odd because even before it was rebuilt it had erractic idle issues.

MorbidHobo

i just figured because mine started to do that after it had been rebuilt

naf

iTrader: (7)

If it's the throttle stop is not resting on the idle set screw make sure the fast idle cam is not holding it open. You can usually open the choke blades by hand, blip the throttle and the fast idle cam will release the throttle. You may have to play with the linkage some if it's sticking. Take a look at the linkage behind and below the choke cover and you should be able to decipher how it works. Play with the linkage (work it up and down) and make sure the fast idle stop is releasing the throttle.