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Discussion Starter #1
Ok, so I have been chasing issues on my 93 G20 for months and I am about out of ideas.

Here are the symptoms:

-Idle jumps up to anywhere between 1300-2000rpm when the TPS is unplugged (making base idle and timing adjustments impossible)
-My gas mileage sucks (16-18mpg) mixed city/highway
-Idle wanders at times and feels slightly rocky.
-Hesitation around 2000-2600rpm when accelerating under light load.

Now in my experience with ser's and g20's, I know when the base idle and timing are off, the car can perform quite bad. So, I'm thinking that most my issues might stem from that. I have set my timing and idle as best I can, but as mentioned above, I can't get the idle to drop in timing mode. I can get it into timing mode, but no matter what I try the revs stay high.

Anyways, I have picked over about every sensor you can think of, checking them with both a multimeter and via consult on my laptop. Everything has been within FSM specs. I have tried swapping many sensors with known good parts with no luck.

The only odd thing I have found is with the AAC valve. If I disconnect the TPS and start the engine, the idle jumps up and the AAC valve will go to about 75% and freeze. Even if I rev the engine it stays locked at 75%.
If I plug the TPS back in the idle drops to normal and the ACC valve drops in the normal range.

So my question is:

What would be the connection here? Why would the AAC valve jump up and freeze only when the TPS is unplugged?

I have tried swapping the whole IACV with an extra one I had laying around (both were cleaned well) but it changed nothing. Perhaps, I have two bad AAC valves? Bad wiring?

Any input is appreciated.
 

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base idle adjustments arent impossible, since u can do them via consult (i think conzult free has it). no disconnect TPS needed.

disconnect TPS probably puts the AAC into some 'safe, prevent stall' mode, since without TPS it can no longer detect when throttle is slamed shut so it can 'catch' the idle via AAC.

what is the AAC value when idling and engine warm? higher than about 30 and the idle screw is set to low maybe

and FYI if your title is accurate, that you have a 'high idle in timing mode', then the solution is simple (and the whole point of idle/timing mode....) to adjust the idle screw and check timing? idle/timing mode prevents ECU from messing with AAC or ignition timing, so u can set both idle (via idle screw) and timing (via timing light etc) correctly.
 

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Discussion Starter #3
what is the AAC value when idling and engine warm? higher than about 30 and the idle screw is set to low maybe
The AAC value will vary between 20 and 40% when the engine is warm. However, some times it does drop to 10% and hangs for bit. It's the second the TPS in unplugged, the value shoots directly to 60-75% and locks. If I plug the TPS back in, the value drops right down.

and FYI if your title is accurate, that you have a 'high idle in timing mode', then the solution is simple (and the whole point of idle/timing mode....) to adjust the idle screw and check timing? idle/timing mode prevents ECU from messing with AAC or ignition timing, so u can set both idle (via idle screw) and timing (via timing light etc) correctly.
I understand the point of timing mode. Believe me, I wish the problem were that simple. This my third sr20 powered car, and this thing has me stumped. I can't find anything wrong. I should have stated before. The idle screw will change nothing. Even if I turn the screw all the way down it the idle will jump up.
 

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I have similar issue. Today I managed to get my 99 g20 into timing mode. After disconnecting the tps the car idled over 1k. I disconnected the iacv valve and the idle went down. I would plug it back and the rpms would go back up. The idle screw does nothing since the rpms are to high. Is it a bad iacv? I will check for vacuum leaks. I will also readjust tps. Any luck on ur case?
 

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I have the same problem. My regular idle is a bit high - ~875 rpm. When I place the car into timing mode – either by disconnecting the TPS or by using the Nissan DataScan “Active Test” Base Idle adjustment mode – the idle goes up to around 1050 rpm. Turning the idle adjust screw on the IACV all the way in doesn't lower the idle below 1050 rpm. Also, disconnecting the IACV while in timing mode doesn't lower the idle below 1050 rpm either. (Disconnecting the IACV in timing mode shouldn't do anything beyond what placing the ECU into timing mode is already doing. Timing mode forces the ECU to stop sending signals to the IACV to adjust idle and it also forces the ECU to stop adjusting ignition timing.)

Why is the idle high in timing mode? When the car is idling in timing mode, the only source of air into the intake is supposed to be the air flowing past the idle adjustment screw on the IACV. If the IACV idle adjustment screw isn't damaged and it is set to the lowest position and if you are really in timing mode, and if your timing is set properly, and if the idle is still high, then either there is a vacuum leak into the intake manifold, or AIR IS FLOWING THROUGH THE THROTTLE BODY WHEN IT SHOULDN'T BE!

My throttle body is definitely closed, and the closed throttle position switch is also set properly. (There are two sensors on the throttle body. On is a potentiometer type thing that sends a signal that varies with throttle position. The other sensor just sends a signal to the ECU when the throttle is in the closed position. The ECU won't go into timing mode if the throttle closed flag isn't set.) How do I know that excessive air isn't flowing through the “closed” throttle body? I've cleaned it twice, and I've confirmed that it really is in the closed position when it should be. (It isn't being held open by the throttle cable or cruise control cable, etc.)

To test the hypothesis that air is getting through the throttle body when it is in the closed position, I designed the following simple test: I follow the FSM procedure for preparing for timing mode, but just before I place the car into timing mode I turn off the engine and disconnect the snorkel at the throttle body. I cover the throttle body opening with a neoprene glove and then reattach and tighten the snorkel. Then I start the car in timing mode. With the throttle body completely sealed closed, and the idle adjustment screw on the IACV set all the way in, the car won't idle – it stalls immediately. With the throttle body sealed, the IACV idle adjust screw is now set too low and the idle screw has to be backed out for the car to run.

Here's what I think this test proves: The source of the excess air in timing mode is the throttle body itself. Either the throttle body is still dirty or it is excessively worn. Too much air is flowing through the throttle when it is in the “closed” position. (It isn't really closed.) That's why I can't get the idle below 1050 rpm when I'm in timing mode. (I know that even a brand new throttle body might leak a smidgen of air when it is in the closed position – but there shouldn't be so much air leaking in that it isn't possible to get the idle down to 750 rpm in timing mode.)

If the base idle is so high – 1050 rpm, why is my regular idle lower? Why does the car idle at 875 rpm when it is not in timing mode? Using a scan tool I can monitor ignition timing at idle and see that the ECU is “trimming timing” - retarding the timing - to bring the 1050 rpm base idle down to 875 rpm. At idle, the ECU retards the timing from 15 degrees BTDC down to 3-7 degrees BTDC in order to get the car to idle lower. (If the throttle gets any more worn/dirty, then it won't be possible for the ECU to trim timing enough to bring the idle down. At that point one would expect the idle to begin to fluctuate higher and to become unstable.) In timing mode, this “trimming” no longer happens, the timing returns to 15 degrees BTDC, and the idle shoots up.

I'm not sure how I am going to address the problem with the throttle body. To clean it any better I would have to not only remove it from the car but also dismantle it. (Remove the butterfly valve and the shaft – like this: http://zilvia.net/f/showthread.php?t=305836.) I'm also not sure how to test for excessive wear in the shaft, bore and butterfly valve. (Are separate parts available to rebuild these??) There is a throttle adjust screw (TAS) on the throttle body itself, but that is set at the factory and the FSM says to never adjust it. (It is there to prevent the throttle butterfly from sticking in the bore in the closed position.) Maybe the best thing is just to get another throttle body from a salvage yard? (New ones are expensive!)
 

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If timing is jumping and with the timing light on it could be the harmonic balance, I took the car to get a smog check they told me timing was unstable I said how so car drives fine yes but timing is not set... looked at the balancer and the rubber was really bad replaced it and timing issue was fixed and smog passed......with flying colors 2cnts
 

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Be careful when "cleaning" Nissan throttle bodies...there is usually a sealant where the butterfly shuts and the throttle body cleaners can easily remove that sealant.
 
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