I bought my car in Dec. 05, (84 Z28 H.O. 5-speed) and it had a marginally high idle (900-1100 rpm). I re-gasketed the water pump a day or two ago, and now it won't idle below 1200 except on startup. It eventually climbs to 1500 rpm when warmed up. I don't see how these are related, but it got worse when I did the repair

When the car is running, the plate with the yellow arrow(name???) is open and quite loose. When I close it, the idle drops and eventually dies if I go too far. Let it loose, it jumps back up.

The plate with the red arrow(name???) is loose when car is off, but is closed under tension when running, even when warm(assuming closed-loop 'cause the thermostat opens). There is no change in idle when I open it.

Surley there are better diagnosing procedures out there, but I don't know them.

 

Push down on the fast idle cam (directly underneath your yellow arrow) and see if the idle drops once engine is hot. If it does, it's something with the electric choke.

 

red arrow is secondary air valve. you should never be able to watch it open, only when you're giving the car gas, and it's under load it'll open.

yellow arrow is choke air valve. it should be open when the car is warm, but on a cold start it'll be closed.

lo-tec is right, just push down on that once the car is warmed up, your idle should drop to normal levels.

 

Thank you for the term lesson.

Nope. Actually the fast-idle cam(FIC) is only pushed up when I push closed the choke air valve. When I release the valve it springs back open. The FIC stays up like that until I push it down, which it basically falls down and stays down. That is what supposed to happen, right??. Well, at that point the idle is still too high.

Oh, just FYI, it's a L69 motor.

 

yea, after the motor warms up, and you tap the gas, it should drop off high idle, and the cam should drop down, and the choke air valve should stay open.

once those are all good (choke air valve open, cam down), re-adjust your idle speed then. If you've got the idle screw backed out, and it still idles high, then check your idle mixture screws, and/or however you adjust the TPS and mixture control solenoid.

Mine did that, but it was because the secondary throttle blades were hanging open due to a bent actuator rod... oops.

 

The Idle Speed Screw(on top of the choke air valve I assume) didn't change anything as I twisted it an entire turn one way or the other. I waited a few seconds and blipped the throttle inbetween adjustments, but nothing seemed to change.

I wouldn't know how to test/adjust the Throttle Positon Sensor or the mixture screws or mixture solenoid. Would you(or anybody for that matter) mind describing it too me or guideing me to a source as to how to test these.

Before I took the water pump off, I got that situation on start-up, and could drop off the high-idle easily, but now it seems like it never falls off. I feel like I must have broke something or done something when I re-did the water pump but I didn't even touch the carb. It got noticably worse when I changed that. I don't know how that might help.

A tech manual for the carb is on the way, but not here yet, so therefore I am dumb as a rock when it comes to carbs.

 

Fast idle screw is at the very bottom directly below the fast idle cam. If the cam stays down it should be off of the fast idle adjustment.

The main idle screw is at the bottom of the primary throttle linkage on the other side.

 

Is the main idle screw the screw that mechanically stops the linkage. It's not even touching the linkage at full close. I tried pushing the linkage farther but it wouldn't go.

I assume the fast-idle screw is fine because the cam-lever thing is staying down.

If i have the wrong screw i'll post a pic of the other side of the carb.

 

yea, I think you've got a few wrong screws.
the screw that is plainly visible in your picture, is to set your cold start mixture (rich or lean), but setting how tight the choke air valve closes at a cold start.

I don't know cc qjets well, but for the overlapping info, I can help you out.

link
here's a mess of info on q-jets, just sift through my webspace there.

Here's a pic of my carb a while ago. the orange arrow is where the idle screw is, just a tiny bit below the orange arrow.
fast idle screw is around the teal arrow.




main things that would increase your idle speed, especially in your case, would be a vacuum leak, or timing too high or something.

 

Well, I haven't touched(or even checked for that matter[shame]) the timing since I bought it, and as the problem has gone through stages, I don't think that is the case. I'm gonna check it anyway.

I think I am down to a vaccum leak somewhere. Umm...Just spray something...don't remeber what. Carb cleaner, or starter fluid, can't remember which.

Thank you for your insight and knowledge.
I'm gonna go hunt down a vaccum leak. Any thoughts and suggestions would be appreciated.

 

you can also use a unlit propane torch.
(either of what you mentioned would work too)

you should be able to hear hissing though, listen carefully.

 

Um, this may sound silly, but would spraying a mist of flammable liquid(or a flam. gas with the propane) around a running engine be kind of dangerous??
Maybe my ignorence is scaring me. Anyone ever blow up doing this???

 

even sillyer, is the irony of you spelling ignorance wrong...

hehehe =]

 

yes, that is ironic

I never had luck with this method myself, but others have, hence I suggested it. I usually just go around checking the hoses, and I find one that fell off or something. With as few vacuum lines as my car has, it's not even worth walking over and finding a propane bottle.

oh yea, and any source of combustion (ie, flame) should be inside the motor, and not on the outside, so you should be safe. Don't do it on on an engine that's really hot, as the exhaust manifolds might be too hot.

 

hahah! =]

 

Yahoo!

I pinched a hose end while the motor was hot and runnin' and it dropped below anything i've ever seen it do. Took it for a drive and it was perfect.
Now it actually idles like the sticker says it should

Thank u

 

excellent. I forgot about that (pinching hoses), another good (safe) method.

 

just FYI, if the pictured "screw" is what you thought was the idle screw you should put it back in the right place. that is the Idle Air Bleed adjustment, and can effect idle and cruise performance signifigantly, as well as fuel economy and throttle "dip in" (really screws with full throttle when you mash it).

the factory spot on this is between 3.5-4 full turns up from bottomed out. the correct way to set it is using a dwell meter hooked to the seemingly useless green harness up near the passenger side corner of the engine compartment, near the climate control stuff.

 

Thank u Doom, for noticing I didn't mention I returned it to its original position, but I did, so no worries.

Could anyone shed some light on this "dwell" I should be measuring.
I don't know what a "dwell meter" even is.

Oh, yeah, and a bit more specific on the "green harness"

Can u compare it to an 88 TBI 'bird? Ive owned it over 4 years and know it inside and out.