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96 Tracker hot idle issue (MAF reverse engineered!) look!
Hi forum members,

I have an issue with the hot idle on my 96 Tracker. It will not regulate down to 800 steadily. It holds steadily at 1000 but then I adjust air bleed screw(closing it) and seems like ISC cannot control idle. I pinched top hose on ISC at 1000 rpm idle and engine nearly stalls, however unplugging the connector does not have the same effect (nearly stalling engine)

I already took off ISC and left it soaking overnight a couple times, checked it against the video of testing ISC on fixkick.com by applying direct 12 v to the ISC connector and see by eye how well it closes and hear how good it snaps. I thought by looking and hearing at the ISC action that it was okey but blowing through the hose with the ISC in my hand without 12v applied I think air leaks through too much.

I screwed in close the air bleed screw and measured depth with a caliper, it measured around 14mm. I then opened it back up to 50% (around 7mm) tried running the car like that and idle went really high and erratic, from 1400 to 2000 rpm up and down, up and down in a way that I could see tachometer needle swinging up and down up and down, not progressively going up or down.

Maybe I'll videotape me testing my ISC so you guys can give your opinion.
1996 Geo Tracker, CAMI, 16 valve, 5sp, 4x4, soft top, 2 door, no a/c
gorky just got his first GOOD MAF, CONGRATULATIONS. !!
wow closed loop and all the trimmings...... wow.
So for good idle , is it in closed loop, i bet it is you told me that.
good the ISC hose test passes, tell me no horrid , leaks, (normal path)
the second test , prove (unplugging the elect) proves the ISC is stuck open.
for sure. the ISC is failing to close. in fact , not even close to closing.

the blow test, must pass, tiny tiny leaks are ok, (imagine a dripping water faucet) but not flood of air.
leave the bleed closed until we fix the real problem
if , the ISC is clean and is working, (it cycles with 12v, and it did)
and you dont mind changing side screw, (whats to lose? its bad, logic) you turn the end screw 5mm,, who knows maybe its already set wrong,.

use lips test.? turn till closed, in hand.
or on car, you idle turn it, until rpm (cw) drops well below 800 (elect, connector unplugged) then plug in electric conn and set bleed if need be. (with bleed closed, id shoot for 600 rpm, this way. then..)
if the the iSC rubber seat is not totally gone,screwing it in, that 5mm allen screw, must drop RPM (unplugged electrically) if not?, its hopeless. (not car the ISC , basket case)

good luck, (you are close to perfect running motor)

all the best !

to be true to facts the bleed sets the ISC to near center of its range.
that is way we must start low, say at 600.
the ECU knows 800 rpm, and tries to hit that , all times hot, no A/C.
when RPM drops the ECU Increases duty cycle to the ISC and more air flows.
if the rpm is above 800 ISC closed,it gets lost.
a new isc is $250 but most can be cleaned and made to work.
Sneaky sneaky isc, ok I will try that next, I'll post later
1996 Geo Tracker, CAMI, 16 valve, 5sp, 4x4, soft top, 2 door, no a/c
The ISC has 1 more trick,
the ISC is not a thermal device, only electric. but it also heats the TB.
if the ISC dont heat fast , then the IAC warms too slow. im 100% sure this is not your issue but is one more ISC trick.

most isc that fail and cycle good can be readjusted, well.
the rubber ring seal was vulcanized on the metal seat (left side)
in the factory, it gets worn and you can compensate for this.
see the red arrow this part fits tight in the left sleeve and
takes persistent cleaning to get fully free. (here)
not carefully the balancing act with the 2 springs..!!!
der guts

[Image: 3_20_04_13_5_10_53.jpeg]

the goals are:
1: get rpm below 800 with ISC unplugged (and bleed closed) 600 is a good place.
2: this allows the ISC (ecu really) wake up, and start regulating idle above 600.. (right now, the ECU can not drop RPM ,so hunts , )
3 then trim the bleed for 800 and you should be near 50/50 duty cycle, close enough and then you can turn on all accessories and the ISC opens more, and idle holds.
Ok, adjusted allen head set screw on side of ISC, with ISC on bench, blowing through top hose (good lungs, lol) closed screw CW until very little air was able to get through while blowing. Put back on car but unplugged electrically.

Started car, engine was very shaky, I forgot RPM's at that point. I just let it run like that for a while. P0300 stored, I thought it was because idle air bleed screw was set incorrectly so I played with that for a while but engine just didn't sound right. I then took spark plugs out and tips were charcoal black. I assume from running rich before I got the good MAF. I cleaned the tips with thinner a brass wire brush and sand paper. Put spark plugs back, started car, engine ran smoooooooth.

Reset CEL, and kept adjusting air bleed screw to 600 rpm with ISC unplugged. Engine ran smooth no matter in what RPM it was. Even down to 500.

I set it at 605 rpm's and then plugged ISC. Waited a new minutes but idle never went up. Engine was already above 187 F. I thought I might have tighten the allen set screw on the ISC too much so I started loosing it a little (kind of difficult to do when ISC installed on engine but doable if 5mm "L" shape allen key is cut down so the back doesn't hit TB)

Adjusting the allen head set screw on ISC only caused an effect when turning CW (RPM's decreased), I stopped messing around with set screw on ISC and adjusted air bleed screw on TB until I got around 800 rpm.

Idle never lost control again, took the car out for a spin (around 10 miles) high loads, and neutral for around 1/4 mile until stop sign, as soon as I let go the gas pedal idle went right back down to 800 rpm and stayed there.

Back at home I pinched the hose of ISC and made rpm's decrease, however unplugging electrical connector on ISC did not cause RPM's to decrease. Still idle keeps holding steadily around 800 rpm, no hesitation or erratic idle.

My engine reaches closed loop in 13.999 seconds =P LOL, what a difference! At this point I'm still unsure whether ISC is functioning right but at least I think the Geo will pass NY State inspection now and will stop burning gas like a V8. I hope no major damage was done to the CAT all this time, oh yeah-no more black smoke.
1996 Geo Tracker, CAMI, 16 valve, 5sp, 4x4, soft top, 2 door, no a/c
that is exactly the way i do it , when>
no scope , no dutycycle meter, and a bad ISC.
if it holds 800 your good. with all electric loads, on, hot, Head lights, fan are huge load and defrost if it still works, few defrost work when old..
it will pass smog, if the CEL is out running, all monitors run out, (ignore evap if it fails to run out, evap can fail to run out with a full tank of gas, normal)
and some states do a fuel cap pressure test on gas tank, no stiffs at all to tail pipe in most states, 96+ and is good reason #1 to have an OBD2 car...
In calif,. far worse , you are not.
how is LTFT hot. ? near 0?
most run -3% (shows if you have air leaks, a good clue to leaks, if huge plus %)

no black smoke, is running Stoich and motor will get 28mpg easy on E10 at 60mph. and motor lasts longer too.

Congratulation on perfect EFI system, all systems GO.
Im happy for you !

whats cool , no new $250 ISC they are expensive. one can fiddle them in to working. even if they leak, a bit....
Just stopping by to confirm with you guys that I started car today, idle went to around 1200 rpm's and after a few minutes it settled down to around 800 rpm.

Checked timing with strobe light again, it was a little off, fine tuned that, and engine sounded even better.

I marked EVERYTHING, distributor clamp bolt against body of distributor after I fine timed it, TPS, P and Q on egr modulator, an other miscellaneous. LTFT hot is averaging -2%

Making that ISC work was aweeeeeeesome. On your post above when you say defrost, is this for front windshield? or the option for hard top? I have a soft top.

Catalyst and EGR System checks are not complete yet.

Thanks again.
1996 Geo Tracker, CAMI, 16 valve, 5sp, 4x4, soft top, 2 door, no a/c
super LTFT, im so glad for you,
yes, the rear window flap had a crude heater at one time.. sucks big time juice. (current) your ISC is working, now....
timing set with the freeze , jumper, ? im sure you did.

cat takes some hot driving and so does EGR n the egr has 2 tests. one for light fast cruise. and one coasting real fast to a stop.
fun seeing a 96 come back to a perfect running condition, yes.. it is.
most states allow one monitor to be , not completed for smog test, (evap is the painful one, )
EGR: (test trip points)
test one over 20mph , rpm 2300 to 3000 (very steady right foot, cruising only,)
test two over 30mph , under 4000 rpm, coasting, , over 22 inches vacuum, off off gaspedal,
happy trails
Ignition timing procedure I followed:


ISC is still not working as supposed to, idle holds steady but when I turn headlights on it drops and ISC can't regulate, it's not bad enough to not let me drive the car, pass inspection or cause any real issues but it bothers me so I purchased an used ISC. Tested both with 12v and what a difference between mine and the one I bought, the replacement one does not leak any air when blowing through and when 12v is applied is a strong snap up and down. I know you show this on video at your page but although video is great, having both side by side in front of me really opened my eyes regarding how inconsistent mine is. The only problem is that all the tubes (air and both coolant tubes) are facing the wrong way, I see that they have little philip head screws that I assume one can take out to remove the tubes so I am guessing they took it apart and put it back wrong? If this is doable please tell me how to do it, I don't want to force it and break it but I don't want to send it back just for someone else to do it and send it back to me wasting time and money on shipping charges.

Picture of two ISC's.

Attached Files Thumbnail(s)
1996 Geo Tracker, CAMI, 16 valve, 5sp, 4x4, soft top, 2 door, no a/c
Actually I just saw a picture of an ISC on fixkick.com it looks like the one I bought, so it must be a different version for 96
1996 Geo Tracker, CAMI, 16 valve, 5sp, 4x4, soft top, 2 door, no a/c

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