Why wont it idle right

[280zx Fever]

Ok i finally got her running on 6cyl after the firing order was wrong. This problem was there before that aswell...

I cannot get it too idle at 1000rpm without retarding the timing down insanely..then it runs like $^!#...

I got it set at 10 degrees atm which is fine but the idle is at 1500-1750 rpm ..... i havent cheack the throttle body except for air leaks but i wouldnt know what to check besides the air leaks..i checked the air boot thats fine.

Now here is a strange thing..i have virtually no blow by when i take off the oil cap thats well and good considering the engine isnt all that old but when i take off the line from the valve cover too the tb and blow in it simulating blow by the idle drops down..

could the valve cover pipe be blocked or something else ?

[ZmeFly]

PVC?

[280zx Fever]

Well all it has is the hose from the valve cover to the tb...

i took it off started it up and it idles @ 1000rpm and slowly dies to nothing... so i think from not getting any blow by its ideling higher,,

what else could it be ?

[sjcurtis]

Does your engine return to 900-1000rpm when the engine reaches "normal running temp" with the timming set to the book positions.

Could it be that your warm up system is working efficiently.

cheers

Steve :classic:

[280zx Fever]

well im only using a 120y raidator and a old thermo fan but i had it up too 1/2 on the gauge and it still idles the same so id say that it doesnt change

[sjcurtis]

Suggest blank the air bypass on the manifold, this can be a bymetal or a black elec initiated valve, if you have the black valve it will be directly below the throttle valve body, just diconnect the loom plug.

If you have the bye metal valve it will be on the upper side of the inlet manifold, near inlet runners 1,2,3 with black hoses to it, blank the hoses. see if your rpm stabalises lower.

cheers

Steve:sleepy:

[280zx Fever]

well i dont know what you mean

there are two hoses going too the TB. one thin that comes from the inlet manifold and if unconnected the car wont start. the other is large and if not connected the car idles fine but dies down.

[sjcurtis]

unfortunately the manifolds and throttle body combinations are in the magnitude of about five diffrent combinations. for the age of your Z, I would expect the Bymetal valve (air bypass). Sorry if my previous was confusing.

if you lean into the engine bay from the passenger side look for a valve just to the rear of the TB, it has two black hose and an elec loom connector attached, it is attached to the manifold by 2 10mm bolts, at the TB on top the closest hose to you goes to the center of the rocker cover from the TB the next hose over on the TB goes to the airbypass valve. isolate this item (either diconnect the elec or blank hoses).

cheers

Steve :classic:

[280zx Fever]

tried that if i take off the small hose it doesnt make a differnce but if i take off the big one it just slowly dies but if i hold my finger over it half it idles right.

[sjcurtis]

Okay got that. The small hose if you blank off the manifold and the hose what happens.

Cheers

Steve

:classic:

[280zx Fever]

Ok i will try tomorrow what is susposed to happen ?

[sjcurtis]

Okay, what you are dealing with.

1. With the engine running at the elevated idle rpm you have an inbalance in the metered air. this inbalance can be from a number of causes, and you have to chase down each possible until all are elliminated, and the correct idle rpm is restored.

2. You also have what you call un-metered air, this is outside air entering any part of the system and in the worst case causing uninitiated engine shut down. The disconnecting of the hose to the center of the rocker cover allowed unmetered air into the system, removing the oil filler cap will do the same.

So now it is metered air and the trimming of metered air you need to concentrate on.

cheers

steve:classic: