ive got a weird problem, My idle always slowely rises to 1000...Ive got an 86 z28 carb 5.0 305 with stick shift.

The fast idle is set to 800 properly, and it seems like it works fine, but when the car heats up, it slowly rises to 1000.

Ive set the idle to about 700, and if I turn the car off when its hot, and I turn it back on, the car starts up at 700, but if i tap the gas, it gets stuck at 1000 coming down, or if I dont, it will slowly rise to 1000...its so weird.

I was planning on rebuilding the carb, but I thought about it, and I dont think that is the problem. Does anyone know what I could check/replace to get to the root of this problem?

Ive did a search, but I couldn't quite make out what solutions are tied to what type of cars, IE TBI, TPI, or Carb fuel injected, etc, so it was confusing. And im pretty sure all of those systems are very different.

Thanks!

 

How strong is your throttle return spring? Does pulling the throttle lever forward (closed) on the carb drop the idle down? What kind of carb is this - Holley, Qjet, etc..?

 

As far as I know its the stock carb...im 99% sure it is.

Really sorry, but Im not a mechanic, im still learning this stuff, so im not sure what you mean...

Where is the spring located? i know the throttle response is very strong, and the car runs very well.

The throttle lever makes it rev...what does closed carb mean? are you referring to the thing on top of the carb that opens and closes?

Sorry for my stupidity.

 

if you carb is stock then more than likly its a qaudrjet 4bbl it may or maynot be ele choke just ck your vacume hoses going to your carb and see if any maybe leaking or just dry or craked that can cause some of your probs esp if you have a vacume choke then thats were i would start beacasu i had a simlier promblem like that and my choke vacum was working some times and not which partily closed my choke but it still run strong just idle high

 

So then rebuilding the Carb is probably a good idea then? I found someone to do it for 170$...a carb shop...and that would eliminate any problems like that...

As for vacuum leaks, Im 90% sure I dont have one, as I had a problem where the car was running shitty and I went over all of the vacuum hoses and made sure they were all connected and the problem went away...

Also no service engine light or anything...dont those show up with a vacuum leak?

 

no not always but if you want to go ahead and rebuid it that would a good to do so but also keep in mind that a good holly or eldbrock is about 250 to 300 bucks new

 

Right but I live in CA, And i couldn't find a single aftermarket carb that is CA legal.

After my post I did find a vacuum leak, and replaced the vacuum hose (it practically fell apart) but the problem remains...so I bought some carb cleaner, and all new vacuum hoses and im going to first off check for leaks, then just replace all vacuum hoses...

If that doesn't fix it idk...

Is there any sensor like the TPS or anything that could be off and cause this problem?

 

Still sounds like an idle leak--either a line or around the base of the carb. Given that the one line fell apart I'd say replacing them all isnt a bad idea. Mine looked fine but when you bent them they just snapped

And is seems to fit with the thing being warmed up is when you notice it---at startup it will be choking itself so you wouldnt notice as much.

 

Well I got out there today and replaced all the hoses going into the carb...but the problem persisted.

I also took a can of carb cleaner and sprayed at the end of each hose, and didnt notice an RPM difference, so no leaks I guess.

Most of the hoses were cracked though, and those miniature hard plastic ones just snapped before I took them off...So i replaced them with rubber (or whatever its made out of) hoses that were a bit bigger... that wont hurt anything will it? they're still airtight.

Also double checked where everythings was going and its all correct, so I really dont know