Corolla ae92 idle rev increases on startup...

[FYADUP]

Hi guys,

Quick querry - My ae92 4age smallport revs up to about 3000 rpm on start up, I know it is cold and she is an old girl, but it has developed more so over the last week.

Even after driving around for a few minutes, I come to a stop at the lights for instance and it revs up and down like a very aggressive lumpy cam.

Any light you guys could shed on this would be tops.

Cheers,
Jason

[jondee86]

The thermostatic idle-up valve underneath the throttle body is
blocked/munted. Check the two small rubber hoses that connect
the cooling system to the valve underneath. Does one get hot
and the other only warm ? If so, the water is probably not flowing
thru the valve, so the wax inside the valve does not get hot and
expand, and the idle-air valve does not get closed.

Once the engine temp gets up to about 80 deg, the engine will
start to cycle on the fuel cut if the revs are over 2000 at idle.

Take the thermostatic valve off and clean it... a lot easier if you
take the whole throttle body off, as the screws are underneath.
Once you have cleaned the valve so that there is no blockage on
the water side, drop the whole thing in a pan of boiling water and
make sure that the valve closes.

You will need a new gasket, and they are found in the top end
overhaul gasket kit, if you happen to have done a head gasket
change recently. Otherwise, you might be able to buy one from
Toyota.

Cheers... jondee86

[FYADUP]

Mate - cheers for that!

Will have a play with it tonight.

[jondee86]

While you are in there, check what happens if you wind the idle
air adjustment screw in a bit. Its down a tube on the side of the
throttle body (sometimes has a black rubber bung in the top).

Fuel cut will happen if the warm idle is over 2000 rpm for ANY
reason, not just because the thermostatic valve is blocked. If the
valve IS working, the cold idle will go high (around 2200 rpm) and
then slowly drop back to 900 rpm or so as the engine comes up
to operating temp. If that is happening, then you shouldn't need
to rip the valve open, and both of those little hoses should get hot.

Cheers... jondee86

[FYADUP]

So as a first port of call - turn her on and have a fiddle with the screw?

[jondee86]

You said you were seeing 3000 rpm on cold start, and that is higher
than you will normally get with the idle-up valve wide open. So just
check that the screw is not all the way open (= up). Screw it all the
way down until it bottoms out and see what happens to the idle. If
you can get the idle under 1700 rpm the lope should go away.

But you have another problem that needs to be solved first. Then
once the idle-up valve is working properly, just trim the idle speed
on a fully warmed engine to 850-900 rpm with the idle air screw.

Cheers... jondee86

[FYADUP]

Thanks mate - will have a play tomorrow and get back to you.

Cheers,
Jason