The ECU 'hunts' when it attempts to control of the idle, loses that control, etc. which makes the idle go up and down. You may want to advise a bit of history about the car, how this issue started, what maintenance you have done, etc. The check engine light must be on with the key on, and off once the car starts. You should also confirm that the car is timed correctly (a compression test will verify engine timing) and that your spark plugs are gapped to .028". You should also advise what the car does from cold start - what cold idle is, what the idle does as the car warms up (and does it warm up? Do you have really good heat in the cab?).
Recently had a distributor oil leak repaired. After, the car, which had been running perfectly, developed the idle issue as well as knocking on light acceleration but only after warm-up. The same general repair shop then declared the problem to be a dirty throttle body and cleaned that with no change in symptoms. Then went to Suzuki where tech informed me that ignition sequence and timing off. Timing set to 8 degrees BTDC. Better, save for idle issue. Plenty of heat. No problems with idle until engine warms up.
I suppose that if a Suzuki tech adjusted your idle/timing, you could return the car to him with the hunting problem and advise that his repair didn't fix this issue?
Normally, setting the ignition timing with the timing light is done after the actual static ignition timing is done (which is based on the engine timing being done properly).
Normally, if you were working on the car yourself, it would be a good idea to start from the beginning, do a compression test to verify engine timing, then check the ignition timing, making sure that you had the proper rotor installed, etc. plugs gapped, etc.
Is your check engine light on with the key on , and off when the car is running? Remember, once your car is warmed up, there is no addition vacuum (which helps the car warm up) so idle problems become more evident. As Aqua says, your hunting idle can often be a product of the idle switch in the throttle position sensor not being calibrated properly. If you work on the car yourself, there are instructions on the forum as to how to do this. Otherwise, you may want to go back to the Suzuki tech, and ask him to check the calibration on the TPS.
It is not tremendously difficult to do, if you know how to use a digital volt meter. That being said, as someone at Suzuki has already worked on the car, I imagine you can contact them and advise that the idle is hunting and ask them to diagnose/repair it. They would hook the car up to a real time scanner, which would show the TPS output at idle - I have no idea, however, what they would charge for this. If you search the forum you should find instructions on how to calibrate the TPS (you will be looking for 16v instructions), to see if you think it is simple enough to do.
Prior to that, however, you may just want to disconnect the connector that goes to the idle speed solenoid (if you follow the small hose that runs off the air pipe at the air filter, it will take you to this solenoid.) When you disconnect the ISC connector, does your hunting stop??
Bex...how do you know all this stuff? Just when you think you know how your vehicle functions you discover things you never knew existed, like TPS, and then other levels of gizmos within that. I naively thought there would be an idle adjustment screw somewhere.
Suzuki autos are no longer sold in the US as you well know. The 'Suzuki of Nashville' setup is an empty shell within which is one technician in what looks like a home garage!! Plus, it is about as far from my home as you would care to go on very rare occasion. I would like to DIY this.
Get yourself a proper factory service manual...or, thank Jim Cameron for posting the 1996 Tracker FSM online for anyone to download for free. Ack's FAQ 1996 Geo Tracker Factory Service Manual
As with many posters, I knew very little about this car when I first got it - I came to Ireland, the suddenly the car wouldn't start - the computer was 'bad'. I sent my computer to someone in the UK, who 'repaired' it for $150. I then found this forum, and learned that, actually, the 'repair' was the replacing of $5 worth of capacitors. I guess it made be a bit pro-active. There is loads of info on the forum that you can learn/study, and some great posters with great info to help you along. The 'hardest' part is diagnosing, based on your symptoms, and that is where the opinions of other posters on the forum come in. And if you have the FSM, it is fairly easy to follow.