4AGE silvertop idle issues

[Lucky13]

Hi all

I've just recently purchased a AE92 hatchback with a silvertop conversion. Unfortunately it has a couple of issues and the first on my to do list is sort out its high idle. It currently sits at around 1500rpm and I'm hoping someone here can shed some light on this.

So far I have done the following...

1 - Checked continuity of plug to ISCV and plug to ECU - everything fine
2 - Checked ISCV operation via direct connection to a power source - this caused the vehicle to either stall out or rev even higher depending on which pin was hooked up, I assume this means that it's working?
3 - Checked centre socket on the ISCV plug for 12V - with the ignition on there is no 12V on the centre socket, it's my understanding that the middle socket should have 12V on it as the ECU switches this to ground via the other two wires to adjust the setting on the ISCV. I tried hooking the middle pin on the ISCV directly to a 12V source and then the other two pins back to their corresponding sockets on the ISCV plug, this didn't work.
4 - I tested all 3 sockets on the ISCV plug with the car running. Socket 1 (closest to the front of the car) had continuity to ground, pins 2 and 3 I got nothing.

This is starting to really confuse me, what am I missing here? Any advice is much appreciated.

[whynot]

It would sound like you are on the right track with testing the power to the iscv. If it has had an engine swap then it's possible someone made a mistake on the wiring. I remember that the iscv, O2 sensor and the vvt solenoid share the same power wire which is fed from the body loom in the vicinity of the ecu. Check the O2 and vvt for power if there's none then look for the connector in by the ecu and track that wire. I had this problem on my ae92 20v swap and whoever did the swap just made the 20v loom plug fit the ae92 one and forgot to swap that one wire over so it had no power.

The other possibility is the ecu has leaking caps which frequently makes them run poorly or have a bad idle. I recommend to repair it or get a repaired one as all 101 ecus will have faulty caps so it's just a case of when it will fail

[GDII]

Does the car have low rough idle when cold and the RPM increases as it heats up?

If you aren't getting 12v to the centre pin the valve will just sit in the middle and not control idle.

[Lucky13]

It seems to be at around 2000rpm when first started then it drops to 1500. It doesn't seem particularly rough but it is hard to tell when it is idling so high.

[Lucky13]

It would sound like you are on the right track with testing the power to the iscv. If it has had an engine swap then it's possible someone made a mistake on the wiring. I remember that the iscv, O2 sensor and the vvt solenoid share the same power wire which is fed from the body loom in the vicinity of the ecu. Check the O2 and vvt for power if there's none then look for the connector in by the ecu and track that wire. I had this problem on my ae92 20v swap and whoever did the swap just made the 20v loom plug fit the ae92 one and forgot to swap that one wire over so it had no power.

The other possibility is the ecu has leaking caps which frequently makes them run poorly or have a bad idle. I recommend to repair it or get a repaired one as all 101 ecus will have faulty caps so it's just a case of when it will fail

So where does the power feed for the ISCV, VVT and O2 come from? Somewhere by the ECU?

[GDII]

Hmmm that's completely opposite to my 3SGE if it's the same problem.

I suggest trying to get power (12V) to the centre pin of the ISCV with it plugged in to see what happens. I tapped into the wire before the valve plug and ran a wire from the B+ pin of the diagnostics plug to this to get 12V and this worked for me.
If you aren't getting 12V to the centre pin with the car switched to ON or even with the car running then that could be your issue.

You are correct with your understanding of point 3 in your first post about operation of the valve and what each wire does. I've actually used a silver top ISCV on a 3SGTE and it was a direct wire in so the system I am familiar with on the 3S engines are the same for the 4AGE.

[whynot]

The plug you are looking for is above where the ecu normally sits. So you will have to pull the passengers side trim off and possibly take the center console and radio surround off to find it. The plug carries the water temp and CEL wires as well as others, It should be a rectangle plug. It's been 5 years since I have had to look at wiring in that area so I can't be sure of the colors of the wires but it should be the same colors as the centre wire at the iscv plug.

[Lucky13]

Hmmm that's completely opposite to my 3SGE if it's the same problem.

I suggest trying to get power (12V) to the centre pin of the ISCV with it plugged in to see what happens. I tapped into the wire before the valve plug and ran a wire from the B+ pin of the diagnostics plug to this to get 12V and this worked for me.
If you aren't getting 12V to the centre pin with the car switched to ON or even with the car running then that could be your issue.

You are correct with your understanding of point 3 in your first post about operation of the valve and what each wire does. I've actually used a silver top ISCV on a 3SGTE and it was a direct wire in so the system I am familiar with on the 3S engines are the same for the 4AGE.

I have tried this also but unfortunately it didn't work.

[Flannelman]

Possible extras.

1. Power Steering sensor. Its under the plenum with two vacuum lines going to it (one leads back into the plenum) Its purpose is for idle up when turning the wheel/placing load on the pump. Very similar to the A/C idle up, which could be looked at too.

2. Check ignition/cam timing.

2. Next is to see if the throttle cable is "loose". This makes sure the throttle blades are resting on the idle screws. Slight tension here will hold them open.

3. Dashpot. The one that looks like a turbo actuator. Its design is to slow the throttle blades down so they rest gently on the idle screws and prevent stalling. If this is sticking high, it will hold the throttle open. It is found under the plenum. Since the plenum is off, take the trumpets off and visually inspect the throttles. Before trying 4. put it back together and use Vasoline or petroleum jelly on the plenum seal.

4. If the insides looked extremely dirty (by oil) and none of the above has helped then the throttles may need to be removed and cleaned. One of the vacuum lines may be blocked. I hope this isn't the case.

5. On the air flow meter, there is a screw that adjusts the idle. BUT it does this by changing the output signal so the ECU reads less or more air. This adjustment needs to be done on a dyno with an air/fuel meter so it doesn't melt anything.