bad idle

[ben1hogan]

Hi, have a 92 geo tracker, 1.6l, 8v 4x4. Live in British Columbia, Canada. My tracker most times, not all times, will idle erratically. Sometimes when coming to a complete stop, it will settle at 800rpm, but most time much less than that, around 400 rpm or will stall all together. When it is acting up, it will stumlble while letting out the clutch from a dead stop. But once the vehicle is moving, it runs through all gears and accellerates just fine. It only gives me trouble when coming to, or at , a complete stop. I have jumped the ECU and only a code 12. I have purchased a used IAC from a good running a motor. I am going to change the IAC tomorrow. The problem seems to happen wether the engine is cold or completely warmed up. Can someone please tell me, if I am on the right track here, or is there somewhere or something else I should be looking at, to solve this problem....thanks

[jtgh]

you did you home work, you are on TRACK, no pun.
can be caused as you say, a dirty IAC or a bad one.
the coil (IRRC) is 30 ohms, so make sure that is ok , the IAC internal coil.
it is just a very fast air solenoid, nothing more.
the ECU modulates it , real fast,
one test is to do a hot foot or what some call feather.
just add a little gas pedal and see if you can correct the idle as it falls.
IF it is is easy to correct idle with your foot , then the IAC is failing. (or?)
on this car , any illegal air leaks are rewarded (not) with a too high idle.
one leaking EGR can destroy any IAC , ops.
make darn sure Main EGR is not sticking open, first.
BTW, since car does hold 800 mostly they you dont have air leaks, because you said drops rpm.
#1 dropper (besides IAC sticking which is #2 IMHO)
EGR introduces exhaust that has no oxygen, which in turns kills combustion at idle.

there is one other thing , the ECU might not be working correctly.
we get , them from time to time an ECU that is sick and works perfect but will not modulate the idle. changing the $1 cap on the ECU bottom left corner fixs 99% of these. (see bad ECU on my site)

There is an acid test for the IAC input.
scope it, ( DSO,etc) or put a volt meter on the two pins by back probing.
volts should be about 6-7vdc. (irrc)
one can pull the connector (iAC) while running ( it is locked don't force it) and see if
idle changes radically , this is a good sign of ECU control reaching the IAC.

if unplugging does nothing, ECU is dead on this line or IAC is jammed. ( clogged etc)


the real deal
http://carfix.stufftoread.com/sensors/iac-wave1w.jpg

it runs at 200HZ ( the frequency never changes)

the ratio of open to closed sets the idle.
this is called duty cycle and is PW modulated by the ecu.
simply said,if the ECU keeps the valve open longer, the idle raises.

nothing magic. The CAS sensor tells the ecu what RPM is and it holds 800 rpm.
but the caveat is that you must tell ECU exactly what IS 800, only once.

I hope i didnt confuse you too much, but this IAC is just an AIR actuator.
some cars use a stepper motor IAC, but this device is FAR better.

The last acid test is can the car hold 800 when you flip on all electrical loads.
a/c HL, fan, radio, defogger, aLL, if it does , you are blessed.

[ben1hogan]

Thanks jtgh. Awesome amount of info. I can indeed save the engine from stalling by feathering the gas. If I feather it, the rpm will rise and settle usually at 800 rpm. Sometimes I have to feather it a couple of times on take off as well. Yes, even with all electrical going ( heater, radio, defog, etc, the vehicle will hold 800 rpm. I will check out that ECU tomorrow, as well as change that IAC, and see what happens. Thanks again for the info

[jtgh]

check coil on iac. I could be shorted too ,overloading ECU.
30 ohms IRRC.
then remove it and flood the heck out of it with carb cleaner.,
you can soak it in paint thinner . for 24 hours , over night etc.

or it the EGR is stuck, EGRs allways stick , it is common as nails.
stick open is bad, that shaft inside must be free and smooth and will cause exactly what you described.

I recommend eGR clean, then IAC second,.
i put all that out for you and the zillion others and the google spider, that sucks them into here. do a googe search ww on EGR and side kick ( we are #1)
many contributors here too. some have done amazing things photographically to help.
some of my stuff is from other that contributed or this site.
cheers

[ben1hogan]

Thanks jtgh will do. Will post follow up with results. jtgh rocks.

[jtgh]

bad data
book in hand, IAC resistance is 11-14 ohms , 1991 FSM quote.
sorry was off, my IIRC was weak.

[ben1hogan]

Checked EGR valve thoroughly. Everything seemed OK. Changed IAC valve. Tracker now idles and runs like a swiss watch. Thanks for the help jtgh. Tracker has never run or idled so good.

[jtgh]

your are like a Lightning bolt, well done .

[95 Tracker]

I have no idea what you said but i have the same problem. it used to idel at 800rpm fine then every onece in a blue moon it would run like crap and the idel would drop and almost stall when all the dash lights would come on and then bounce up a little and drop again. but know it does this all the time. so i took it into my hands on how to fix this. so i took the intake tube off and cleaned all the black crap aroung the butterfly flap. started it up and it ran at 1500rpm. i was at my friends house so i drove home stoped at a traffic light dropped to 1200 got home went back to 1500. it seened like it wanted to stay at 1200 but slowly rose to 1500. shut the car off call my dad and ask him if i can adjust the throttel cabel, he said adjust it while the car is running so i turn the car on now it's ideling at 800rpm. so i shut the car off and turned it back on its at 1200 tap the gas and it setteled at 1500. so i got it to idel lower by adjusting the cabel. it now idels at 1500 on startup and idels warm anaywhere from 700 thru 1200rpm. i don't know why it is inconsistant thanks for any feedback.

[jtgh]

hello 95tracker
clean EGR, Clean IAC, that is hard to understand?

your cable adj. is completely not, how the system works. Sorry!
it is not a carb.
95 what , 8v , 16v ? auto manual. all are diff. to get help tell us what you are driving.

first step is to adjust that throttle cable so it is loose and has no bearing on idle.
the ECU controls the idle
but to set the idle so that the ECU can do its job ,

first off , if you have an 8v , any air leak ,into the induction will cause high idle.
Guessing here, 8v.
the 8v will race at any leak,
that is how the ECU works on an 8v, you make an air leak and the ECU MATCHES
perfect gas ARF (air fuel ratio).

you should create your own post, and tell car , engine and drive line with number of valves and doors, and speeds. and w4d .
then state your symtoms both hot and cold engine.


after getting the throttle cable set loose ( there is a spec for this)
I had an old motorcycle that ajusted that way . was junk.
then there are only 1 or 2 adjustments to make, on most 95's the one adjustment
is on the throttle body, there is an air bleed screw,
one adjusts the air blead screw for 800 hot.

how ever, the EGR must must not be stuck open or leaking
the IAC/ISC can not be stuck open (racing)

after you set the idle properly.
the IAC then controls the engine under all condtions, this happens because
the ECU controls the IAC, the ECU opens to closes it depending on the load you place upon the engine.
that is it.

Idle is the last thing to fix (adj) on any engine, 1920 to date.
tune up, air leaks, PCV clogged, air cleaner dirty.
first fix and tune a car then set the idle.

hope my comments are clear.
if it is not please ask detailed questions, can answer an kind. on this driveline.
I will try my best..
cheers