Weird 4A-GE idle problem

carina4age
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Weird 4A-GE idle problem

Postby carina4age » Wed Jul 18, 2018 9:08 am

Hello,

I have 4age tvis in my toyota carina, and the idle is making me nuts. In warm summer days it drops down to 500rpm, but when i put heater to warm position, idle slowly raises to ~900rpm. In winter car idles about ~1100rpm but drops wery low if i let it run and sit still. It works good, no misfires or anything like that. I have burped coolant many times, adjusted tps, new oem thermostat, timing was good, no CEL, iacv cleaned two times, i boiled it that i can see it moves, it does. Can coolant temp sensor be failing somehow?

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jondee86
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Re: Weird 4A-GE idle problem

Postby jondee86 » Wed Jul 18, 2018 4:55 pm

What you describe are classic symptoms of how an engine behaves if the AAV (ISCV
by another name) is not working. If you have have placed the whole valve in boiling
water and seen that it moves 3 or 4mm, then the next thing to check is if the water
from the coolant piping is actually circulating thru the valve.

Easy first check is to feel the two small rubber hoses that connect to the valve once
the engine is at operating temperature. They should both be hot. If one is hot/warm
and the other cold/cooler, then there is a blockage somewhere. It could be in the
valve itself... did you check that water could freely flow in one water connection and
out the other? Most often the valve gets blocked with rust particles or maybe a stray
blob of silicone from cooling system repairs.

If the valve is good, then check that the small hoses are clear, and that coolant flows
out of the metal tubes that the hoses are connected to on the engine.

Cheers... jondee86
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carina4age
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Re: Weird 4A-GE idle problem

Postby carina4age » Wed Jul 18, 2018 8:19 pm

I have checked the small rubber hoses two times and water flows. Also tested that water flows trought iscv.
And both hoses are warm. Sometimes the idle drop is very fast, so i think the wax pellet moves so quickly. I cant understand how the cabin heater effects the idle speed.

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jondee86
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Re: Weird 4A-GE idle problem

Postby jondee86 » Thu Jul 19, 2018 1:06 am

Hmmm... my bad :oops: I think that I read your post too quickly, and didn't pick up
that your engine is actually doing the opposite to what it would if the AAV was blocked.

To be clear; if the AAV is working the engine idles high on cold start and tapers down
as the engine warms up. Normal is 2200rpm falling to around 900rpm. As you have seen,
the wax pellet in the AAV responds quite slowly to temperature changes, so it is not
capable of altering the idle speed quickly.

If the AAV is blocked/not working the engine may be difficult to start and when it starts
it will idle low. As the engine warms up the idle will rise. The process is not automatically
regulated, so you have to choose a happy medium for your idle speed. For example,
800rpm when cold rising to (say) 1200rpm when at operating temperature.

The heater and AAV water piping are interconnected, so it is possible that opening the
heater valve could have some effect on the idle, but I can't guess what it might be.

I suspect that your AAV is faulty. To narrow down the possibilities, you should disable
the AAV by placing a small rubber bung in the AAV valve air passage in front of the
throttle butterfly. Once that hole is blocked the AAV can no longer have any effect on
your idle speed. Adjust the idle speed to a happy medium as described above using the
idle air adjustment screw down the tube at the side of the throttle body.

If the idle is now consistent... low when cold and rising as the engine warms up, then
see is you can find a replacement AAV.

Cheers... jondee86
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carina4age
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Re: Weird 4A-GE idle problem

Postby carina4age » Thu Jul 19, 2018 3:13 am

Cold idle is good, ~2000rpm, problems start when engine is hot. When i stop to traffic lights hot idle is 900-1000rpm in summer. In winter about 1100-1200. But if there is traffic jam or something like that and i need to stay still long time, idle drops very low, around 500rpm. I will try to block the hole and see if that works. I also ordered new radiator cap, because my current one have seen better days.

totta crolla
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Re: Weird 4A-GE idle problem

Postby totta crolla » Thu Jul 19, 2018 3:26 am

A couple of things.
Does the idle increase if you add electrical load, heater fan etc ?
Check the spark plugs immediately after the idle has dropped to its lowest, the engine may be running very rich. Is there an O2 sensor fitted ?

carina4age
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Re: Weird 4A-GE idle problem

Postby carina4age » Thu Jul 19, 2018 6:32 am

Idle drops more down low if i add electrical load. Yes there is o2 sensor fitted.

totta crolla
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Re: Weird 4A-GE idle problem

Postby totta crolla » Thu Jul 19, 2018 11:34 am

Is the idle up computer fitted ? (It should be attached to the ecu)

carina4age
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Re: Weird 4A-GE idle problem

Postby carina4age » Thu Jul 19, 2018 11:43 am

I blocked the hole with tape in throttlebody and idle was 500rpm so the problem is in the aav. Can it be repaired somehow? Or can i block it permanently? 4age is quite rare thing in here finland, so finding a working replacement part will be challenge.

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jondee86
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Re: Weird 4A-GE idle problem

Postby jondee86 » Thu Jul 19, 2018 2:41 pm

Here is a diagram showing the AAV...

Image

I have never heard of anyone repairing one, but apparently you can still buy them
new (for big $$$)....
http://jp-carparts.com/toyota/part_deta ... rt=1173682

I'll have a look in the shed later today. I might have one there that you can have
for the price of postage from New Zealand. The 4AGE is not so rare down here :)

Cheers... jondee86
Give a person a fish, they eat for a day. Suggest they search before posting, and they learn a skill for a lifetime.

carina4age
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Re: Weird 4A-GE idle problem

Postby carina4age » Thu Jul 19, 2018 8:45 pm

That would be awesome!

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jondee86
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Re: Weird 4A-GE idle problem

Postby jondee86 » Thu Jul 19, 2018 9:30 pm

Hmmm... it seems that your AAV is operating much as expected except for the
idle dropping to 500rpm sometimes. As totta crolla points out, when you add electrical
load a small solenoid valve should open to allow extra air into the manifold via one of
the small spigots on top of the throttlebody. This should keep the idle near constant.

Further, if you have airconditioning, there should be a separate A/C idle-up solenoid
hooked up to one of the larger spigots on the AAV to allow extra air into the manifold
when the A/C compressor switches on. If this one is not working (and you are using
A/C) the idle can drop to 500-600rpm when you are stuck in traffic and using the A/C.

If none of these conditions apply, and the the idle speed can jump up and down quickly,
it is most likely that something broke inside the AAV allowing the valve to "float" and
randomly move with vibration and airflow changes.

Anyway, I found the AAV :) Boiled it and the valve could be seen to move about 6mm
from 10 to 100degC. Water passage is clear, so seems 100% good to go. Found a new
gasket and can probably supply an O-ring as well. If you want it email or PM me your
delivery address and I will find out the shipping options.

Cheers... jondee86
Give a person a fish, they eat for a day. Suggest they search before posting, and they learn a skill for a lifetime.

carina4age
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Re: Weird 4A-GE idle problem

Postby carina4age » Fri Aug 10, 2018 8:41 am

I installed used aav yestersay, thanks jondee, and idle seems to work like dream now :) so case is closed.

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