4AGE 16V - Idle Hunting

[Tom4AGE]

Hmmmmmm, MAP sensor or AFM?


Idle hunting diagnosis is a bit different between them.

My engine has a MAP sensor, I hope you can help

[EVOSTi]

My engine has a MAP sensor, I hope you can help

lots of people have made suggestions, have you tried any?

[The Witzl]

The most typical reason for an otherwise OK 4AGE engine to "hunt" for idle is a faulty auxilliary air valve.

Look up the 4age book - this is the little doovey thing that bolts underneath the throttle body and has coolant plumbed up to it. How it is supposed to work is it has a wax pellet inside that is solid when cold, and allows air to pass through a valve, thus increasing idle. When the wax warms up thanks to the warm coolant, it melts and closes this air valve, thus dropping idle back down to normal.

What eventually happens is that the wax goes shit, and the valve screws up - causing the valve to open and close randomly, giving you this strange hunting idle which otherwise shouldnt happen.

There is a trick to test this out......
when your idle is hunting and the engine is at operating temperature, try blocking off the port just in front of the butterfly for the aux air valve with your finger.... if the idle drops - BINGO, you have a dodgy aux air valve.

Here - read this and GO CHECK IT!

http://www.toymods.net/TechDocs/4age_book/efi/fi_87.jpg

[Tom4AGE]

its your TPS, set it correctly.

unscrew the two phillips head screws on the TPS (black plastic thing opposite the throttle on the throttle body) and swing it from side to side (the screw holes are slotted for this reason)

I think you are right. When I first set the TPS, the idle went very high. I adjusted the idle and now when it is warm there is no hunting. There is some hunting when cold but it is far less severe than before and it is more random. I will check the timing tonight and recheck the TPS
Thanks

[Tom4AGE]

It could be a number of things

1. First bleed the coolant properly as mentioned above (most likely cause)

2. If its not the coolant then check for air leaks.

3. If there are no air leaks then it could be the waxstat (they fail all the time in the uk). take off all the intake hosing and start the car, inside the throttle body at the 5 o'clock possition is a small hole (about 2 cm into the throttle body) stick your finger over it. The the engine dies, its the waxstat. You can either replace the throttle body, or block off the aforementioned hole and install a manual choke, using any old solinoid.

I think the waxstat is OK, but not sure. Inside the throttle body is 3 holes. 2 larger ones at 2 oclock and 5, and a small one (about 4mm diameter) at about 4 oclock. Do you know what the small one is, is this the waxstat. I think the large one at the top is the idle adjust, and the large one at 5 oclock is the aux air valve, which is working OK
Thanks

[Tom4AGE]

The most typical reason for an otherwise OK 4AGE engine to "hunt" for idle is a faulty auxilliary air valve.

Look up the 4age book - this is the little doovey thing that bolts underneath the throttle body and has coolant plumbed up to it. How it is supposed to work is it has a wax pellet inside that is solid when cold, and allows air to pass through a valve, thus increasing idle. When the wax warms up thanks to the warm coolant, it melts and closes this air valve, thus dropping idle back down to normal.

What eventually happens is that the wax goes shit, and the valve screws up - causing the valve to open and close randomly, giving you this strange hunting idle which otherwise shouldnt happen.

There is a trick to test this out......
when your idle is hunting and the engine is at operating temperature, try blocking off the port just in front of the butterfly for the aux air valve with your finger.... if the idle drops - BINGO, you have a dodgy aux air valve.

Here - read this and GO CHECK IT!

http://www.toymods.net/TechDocs/4age_book/efi/fi_87.jpg

I checked this last night and it appears to be OK. I still have some hunting when the engine is cold, but putting a finger over this hole does nothing to help the idle hunting
THANKS

[The Witzl]

damn.... well sounds like you might have another problem.
I have driven a 4age before with a blown head gasket... the idle hunted really badly on that one! Maybe you have a BHG?

[walu]

My experience with this was a vaccuum line at the rear of the butterfly came off, and the idle would fluctuate exactly as you describe 800-1500-800-1500 etc. I put the vaccuum line back on - back to normal.

That's my 2 cents worth. Good luck.

[wa5]

my spares car/ paddock basher is an 86 AE82 twin cam with a slight blown head gasket. the car has hunted badly when idleing from the day I got it. the problem only appeared after the car warmed up.... today I disconected the TPS and the idle stabilised at around 1000 RPM (I would have tried to adjust it but the screws were grown in.

[16vgeo]

Same thing happened to me and it ended up being the Choke control which sits underneath the throttle.

It can easily get choked up with dirty fuel etc or sometimes they just become faulty. On my AE82 twincam it was originally just dirty, it was cleaned and idle was fine for around 3 months and then the unit became faulty. It does make sense however to check the coolant first.

Got to be one of the most annoying problems.

[takai]

Same thing happened to me and it ended up being the Choke control which sits underneath the throttle.

Holy Thread Resurrection Batman

Anyway, FWIW.
That has already been discussed. Its called an ISCV or Auxiliary Idle Control Valve, or similar.

My hunting idle problems with 4AGEs in the past have been caused by the following (not all at once, separate incidences):

• Vac Leak
• TPS
• MAP Sensor
• BHG
• Coolant Temp Sensor
• ISCV
• Exhaust Leak (could have been just a coincidence)

Start checking these off.

[grey_nomad]

One more problem I found on my son's 4age.

It's an fwd cut/shut inlet manifold. The throttle bottle is not squarely welded onto the manifold (this is how it came when he bought the car).

It occassionaly hunts at idle when hot.

After eliminating all the possible causes as listed above, it turns out the throttle cable was not in line with the throttle quadrant. The wear on the throttle spindle allowed the butterfly to move to one side when open, and when closed, would bind on one side and not fully close. Result - extra air past the throttle plate and hunting.

Rejigging the cable mount so the cable is in line with the throttle quadrant should fix it.