no opposite low cold with a dead IAC.... i answered from low idle..cold.. so forget my post.
the iAC can fail in many ways, like all things can, (as they say, good./bad or ugly) ugly has many forms....damage has no limits on earth.
1: sticks closed.
2: sticks open
3: go out of calibration or go non linear (psychotic, like thermostats love to do.. "unpredictable")
lets review some basics here, this 16v engine, adds fuel to air, (by calculation, EFI magic does that. and varies by mode, "crank, cold idle, warm and hot modes")
facts as i know them.... (helps diagnosis, knowing this)
when you crank the engine cold, fuel is added by using tables, the ECU has IAC tables, in perm,, memory. it uses those tables to add fuel, to match the iAC air flowing. (maf mostly useless and dead cranking so cant us that. ) These fuel tables, even calculate fuel evaporation rates, in super cold weather, like at -40C (or F). when fuel refuses to evaporate, (like in Alsaka) now you know why it richer, do to this one fact.
if the iac is not open the engine wants to flood. see why? (NO AIR supply!)
now pretend the engine starts, now it's in cold run mode, dead cold, the MAF is not very accurate at low idle speeds (read near useless) so the ECU will use tables for the IAC
to help the maf gross errors, and the 02 is dead cold so that is of zero help here. the IAC is key device. In fact most maf cars, ignore the maf in this mode. newer cars run dual meters, MAP/MAF to cure issues here.
now the engine warms up, not in 1minute.. ? not ever with a cold block. (use a real thermometer or scan tool reading ECT for this data)
you need to learn this. by using a temp gauge on your engine, and see when 150F temp is hit in time. it's like 10mins. right? (im sure your not burning NITRO) LOL
so in those 10 minutes (70f to start) the IAC slowly closes and idle drops. to 800. (most ISC run at 1500 rpm cold and wind down to 800 (the 800 is ECU's ISC servo taking command and the closed loop 02 activating.)
and regulates now at 800, the ISC goes ONLINE and regulates at 800 rpm, i prove that by turning on the headlights and heater fan to high. and RPM does not drop.
it can blip down but bounces back to 800 this is sure sign that the ISC is work, some what. (the ISC is an regulating RPM servo system it too , is a closed loop system hot, idle , just like the 02 servo system)
all my words here are using real tools, not dash tools.
real tacho , real temp gauges. (so i can never chase my tail)
FLOWS OF AIR:
now to answer 16v air flows and RPM as you asked
the 16v when cold is rich, running. (by design an fuel tables inside ECU) MPI needs less RPM that TBI because port injector is 10x better.
when rich , all air leaks, from any sources cause and illegal excess RPM, (metered)
if the IAC leaks , this is leaking metered air, not fresh outdoor unmetered air. (called illegal air leaks, vacuum leaks or for example the PCV hose cracked sucking in fresh air.)
the IAC metered air , will cause rpm to rise. not lower.
in fact, at this same moment , pressing the throttle does exactly the same thing, it lets in metered air. (ecu matches all this new air with new exactly mixed fuel)
in fact, if you look more closely, see the IAC is just a TV bypass device,
seen in my slide show,.. page 3,frame 40
see that here, the IAC is just holding open the TV (virtually) for you, so engine will not stall and engine don't flood the CAT with loads of raw HC (gas) (lacking proper air to run RIGHT)
http://www.fixkick.com/fresh-air/Slide_S...ge_40.html
the down shot to a bad IAC is what? (stuck closed)
1: wasted fuel. (and more for folks that warm cars up parked)
2: cylinder ring wear, excessive. (too rich washes off protective oil film)
3: CAT damage. (progressive)
4: slower warm up's. unless you drive it cold. (best is to do just that,gently)
5: spark plugs foul faster.
that first thing i watch on all G16, is the thermostat, how long it takes to get closed. and hit 180f, old stats, are slow,and waste fuel, and wear engine out faster.
then i watch RPM to see when the IAC closes, i want it to work correctly, at 150f end point., so I watch it like a hawk.
cheers, and happy trails.
seen many old sidekicks now with a tacho that read totally wrong. they can do that.
i never believe gauges on cars, and for sure this old, i do what is called, validation.
like here. (using real tools)
here is me doing just that.
see this, the meter has no numbers. so it just a toy, so here is a new sender, and my IR gun proof that it really is 195 f
now on just this car, i know where normal is.... see how i did that?
![[Image: meter-T-only1.jpg]](http://www.fixkick.com/sensors/sensor-icons/meter-T-only1.jpg)
now a tacho.
i have 2, one is optical , can see pulley slip and check idle for timing , while never leaving confines of hood. (lazy) $12 on fleabay
or electric.
the hand held tachometer electric must be told, 4cycle, and 4 cylinder to work
or get a timing light that has this built in.
or clamp on tacho (HV wire)
or DMM with a tacho.
http://www.ebay.com/itm/Digital-Tachomet...xyzHxRO7bC
this link on fee bay, you connect to coil minus (can very hard to do that,)
or to the noise suppressor brown wire , called Tacho line.
there vast ways today to get good tacho readings, not one on the dash.
if you drive off cold, and keep moving
you dont need the IAC.
see why?
i have DMM that does tach.
timing light,
and the opto tach.
the opto wins, most easy , no wires. way, no contact. safer , faster, and dead accurate.
the thermal couple probe in my meters do great for thermal accuracy, with due care used.... (technique)
as a tech, you learn fast to use tools that dont lie to you,.
measurement errors the top way to make me go WRONG, wastes the whole day.. zero productive. so the tools are free, see why?
no move, that it too pain ful. must fix wifes car. now.
idle issues are the most complex.
Due to ECU modes .
and that nature hates a vacuum,,,, cept in outer space,
watch the movie, the martian. (i read the book too, its 10x better)
watch that man fight vacuum. every moment of his life.
see how nature does hate at VACUUM but in this case, it hates, you for not being in a vacuum. (same reason, seals.)
the other big fight for man kind is Entropy.
all things want to turn in to something else. (like steel to iron oxide) and the whole universe. ,mans toys are all short lived.
all we do.
is slow the entropy (called service)
or erase it and start anew.
the iAC can fail in many ways, like all things can, (as they say, good./bad or ugly) ugly has many forms....damage has no limits on earth.
1: sticks closed.
2: sticks open
3: go out of calibration or go non linear (psychotic, like thermostats love to do.. "unpredictable")
lets review some basics here, this 16v engine, adds fuel to air, (by calculation, EFI magic does that. and varies by mode, "crank, cold idle, warm and hot modes")
facts as i know them.... (helps diagnosis, knowing this)
when you crank the engine cold, fuel is added by using tables, the ECU has IAC tables, in perm,, memory. it uses those tables to add fuel, to match the iAC air flowing. (maf mostly useless and dead cranking so cant us that. ) These fuel tables, even calculate fuel evaporation rates, in super cold weather, like at -40C (or F). when fuel refuses to evaporate, (like in Alsaka) now you know why it richer, do to this one fact.
if the iac is not open the engine wants to flood. see why? (NO AIR supply!)
now pretend the engine starts, now it's in cold run mode, dead cold, the MAF is not very accurate at low idle speeds (read near useless) so the ECU will use tables for the IAC
to help the maf gross errors, and the 02 is dead cold so that is of zero help here. the IAC is key device. In fact most maf cars, ignore the maf in this mode. newer cars run dual meters, MAP/MAF to cure issues here.
now the engine warms up, not in 1minute.. ? not ever with a cold block. (use a real thermometer or scan tool reading ECT for this data)
you need to learn this. by using a temp gauge on your engine, and see when 150F temp is hit in time. it's like 10mins. right? (im sure your not burning NITRO) LOL
so in those 10 minutes (70f to start) the IAC slowly closes and idle drops. to 800. (most ISC run at 1500 rpm cold and wind down to 800 (the 800 is ECU's ISC servo taking command and the closed loop 02 activating.)
and regulates now at 800, the ISC goes ONLINE and regulates at 800 rpm, i prove that by turning on the headlights and heater fan to high. and RPM does not drop.
it can blip down but bounces back to 800 this is sure sign that the ISC is work, some what. (the ISC is an regulating RPM servo system it too , is a closed loop system hot, idle , just like the 02 servo system)
all my words here are using real tools, not dash tools.
real tacho , real temp gauges. (so i can never chase my tail)
FLOWS OF AIR:
now to answer 16v air flows and RPM as you asked
the 16v when cold is rich, running. (by design an fuel tables inside ECU) MPI needs less RPM that TBI because port injector is 10x better.
when rich , all air leaks, from any sources cause and illegal excess RPM, (metered)
if the IAC leaks , this is leaking metered air, not fresh outdoor unmetered air. (called illegal air leaks, vacuum leaks or for example the PCV hose cracked sucking in fresh air.)
the IAC metered air , will cause rpm to rise. not lower.
in fact, at this same moment , pressing the throttle does exactly the same thing, it lets in metered air. (ecu matches all this new air with new exactly mixed fuel)
in fact, if you look more closely, see the IAC is just a TV bypass device,
seen in my slide show,.. page 3,frame 40
see that here, the IAC is just holding open the TV (virtually) for you, so engine will not stall and engine don't flood the CAT with loads of raw HC (gas) (lacking proper air to run RIGHT)
http://www.fixkick.com/fresh-air/Slide_S...ge_40.html
the down shot to a bad IAC is what? (stuck closed)
1: wasted fuel. (and more for folks that warm cars up parked)
2: cylinder ring wear, excessive. (too rich washes off protective oil film)
3: CAT damage. (progressive)
4: slower warm up's. unless you drive it cold. (best is to do just that,gently)
5: spark plugs foul faster.
that first thing i watch on all G16, is the thermostat, how long it takes to get closed. and hit 180f, old stats, are slow,and waste fuel, and wear engine out faster.
then i watch RPM to see when the IAC closes, i want it to work correctly, at 150f end point., so I watch it like a hawk.
cheers, and happy trails.
seen many old sidekicks now with a tacho that read totally wrong. they can do that.
i never believe gauges on cars, and for sure this old, i do what is called, validation.
like here. (using real tools)
here is me doing just that.
see this, the meter has no numbers. so it just a toy, so here is a new sender, and my IR gun proof that it really is 195 f
now on just this car, i know where normal is.... see how i did that?
now a tacho.
i have 2, one is optical , can see pulley slip and check idle for timing , while never leaving confines of hood. (lazy) $12 on fleabay
or electric.
the hand held tachometer electric must be told, 4cycle, and 4 cylinder to work
or get a timing light that has this built in.
or clamp on tacho (HV wire)
or DMM with a tacho.
http://www.ebay.com/itm/Digital-Tachomet...xyzHxRO7bC
this link on fee bay, you connect to coil minus (can very hard to do that,)
or to the noise suppressor brown wire , called Tacho line.
there vast ways today to get good tacho readings, not one on the dash.
if you drive off cold, and keep moving
you dont need the IAC.
see why?
i have DMM that does tach.
timing light,
and the opto tach.
the opto wins, most easy , no wires. way, no contact. safer , faster, and dead accurate.
the thermal couple probe in my meters do great for thermal accuracy, with due care used.... (technique)
as a tech, you learn fast to use tools that dont lie to you,.
measurement errors the top way to make me go WRONG, wastes the whole day.. zero productive. so the tools are free, see why?
no move, that it too pain ful. must fix wifes car. now.
idle issues are the most complex.
Due to ECU modes .
and that nature hates a vacuum,,,, cept in outer space,
watch the movie, the martian. (i read the book too, its 10x better)
watch that man fight vacuum. every moment of his life.
see how nature does hate at VACUUM but in this case, it hates, you for not being in a vacuum. (same reason, seals.)
the other big fight for man kind is Entropy.
all things want to turn in to something else. (like steel to iron oxide) and the whole universe. ,mans toys are all short lived.
all we do.
is slow the entropy (called service)
or erase it and start anew.
http://www.fixkick.com