the ISC is out of control or bad AFR AF/R (fuel mix is way off)
Red 16v :
out of control happens for many reasons.
please post surge range.? this is key, fact.
that surge is the ISC (ECU slave device) surging to hit 800 RPM, what is your Surge range, 500 to1000 , 1000 to 1500 ? or ??????????????
the ECU is programmed to hold 800 hot. and if it cant do that some ECU surge and others just freeze at the limit, (software differences by year, )
if the ISC is not causing the surge, then the AFR (air-fuel-ratio or fuel mix) is way too lean, all gas engine surge like that even carbs (lean).
there are tests we can do to prove that.
the ISC can cause the surge, for these reasons., and more. (in each case the failure puts the ISC out of control (out of authority its called)
1: lean AFR, and RPM way too low,
2: so rich AFR engine has gross misfire. and RPM way too low.
3: EGR sticking open. causing rpm way too low. (way too low means ISC can not get it to the perfect 800 rpm)
4: Intake, induction path has air leaks causing #1, all hose, and air pipes from MAF to intake valves.
5: RPM way too high, ISC cant get it to 800, so surges. , IAC (thermal valve ) stuck open and idle way too high.
6: throttle cables sticking, (up to 3 cables must be set loose, throttle, cruise, and A/T kick down cables.. they must not interfere with the throttle at idle.
7: someone messed with the throttle plate stop screw ,an the butterfly plate is no longer closed, it is must be. its 99.9% closed.
8: someone fiddled the idle duty cycle speed bleed screw on top of the Throttle body, (black cap plastic under it) and its was set way off , so bad
the ISC can not get 800 rpm.
9: the ISC might have its range limited, it still works but it can open all the way or close all the way, so fails. clean it.
TESTS:
im sure if you unplug the ISC it will stop the surge. (electr, connector (has lock lever dont force it , suz, dont sell em)
what is RPM now? hot?
then pinch the ISC air line.
what is RPM now.?
put back the connector
what is RPM now, still pinched? hot.
this test tells me the total air flow , natural, and a cause of wrong.
here are all the air paths,
on a hot engine the IAC is 100% closed.
The throttle valve the same.
so the only air supply is ISC and the bleed, if not?, it will surge, or freeze a the wrong RPM..
all air is metered, if not? , it goes lean, when not in closed loop.
![[Image: induction1a.jpg]](http://www.fixkick.com/fresh-air/Slide_Show/images/induction1a.jpg)
im glad its a 16v its Throttle body is simple, unlike the horrid complex 8v TB., that love to leak in very odd ways.
if you screw in the bleed screw 100% and the engine races way over 800 RPM , you do have air leaks, One more test, pass or fail.
even injector base cushions can leak.
mine had a cracked, main huge air intake tube (near #3 in photo), (all aluminum) the back rear alum. base mount was broken, and it sucked in air right there, at the break. took mirror to see it, on car.
as the leaks add up,, it exceeds the authority of the ISC and can hunt.
you can change the Autority rage (called dutycycle) with the bleed.
in fact screwing in the bleed can hide small leaks.
or unscrewing it for idle too low.
the bleed is actually set in the factory for 50% duty, it can increase and decrease RPM equally, by 50% . say 400 RPM to 1200 RPm (crude guess, as there is no spec on this)
if your car was new.and you have a leak of air , more the 400 rpm worth, the ISC might surge, because, it cant attain, at least 850 RPM. if it can't some ECUs surge.
one guy said mine never surges, with on purpose leaks. sure...
that is because your software is different. some ECU do, others don't, ive tried many, some just rail and freeze there.. ECU waiting for ever, hoping RPM drops. to below 850.
rule 1: hot engine.
metered air leaks cause racing (1 example is IAC stuck open or throttle stuck open) if too much, it can surge.
un-metered air leaks causes lean, an surging. ( say a crack in any tube or hose.)
be glad car is not throttle by wire, omg. complex.
unmetered air is air the MAF can't see, the maf is the Air meter. (mass air)
i need RPM range first. surge range so i can point more directly.
if car was 1996 and above. we can check for closed loop at idle to see if AFR is right. but no scan tool here.
Red 16v :
out of control happens for many reasons.
please post surge range.? this is key, fact.
that surge is the ISC (ECU slave device) surging to hit 800 RPM, what is your Surge range, 500 to1000 , 1000 to 1500 ? or ??????????????
the ECU is programmed to hold 800 hot. and if it cant do that some ECU surge and others just freeze at the limit, (software differences by year, )
if the ISC is not causing the surge, then the AFR (air-fuel-ratio or fuel mix) is way too lean, all gas engine surge like that even carbs (lean).
there are tests we can do to prove that.
the ISC can cause the surge, for these reasons., and more. (in each case the failure puts the ISC out of control (out of authority its called)
1: lean AFR, and RPM way too low,
2: so rich AFR engine has gross misfire. and RPM way too low.
3: EGR sticking open. causing rpm way too low. (way too low means ISC can not get it to the perfect 800 rpm)
4: Intake, induction path has air leaks causing #1, all hose, and air pipes from MAF to intake valves.
5: RPM way too high, ISC cant get it to 800, so surges. , IAC (thermal valve ) stuck open and idle way too high.
6: throttle cables sticking, (up to 3 cables must be set loose, throttle, cruise, and A/T kick down cables.. they must not interfere with the throttle at idle.
7: someone messed with the throttle plate stop screw ,an the butterfly plate is no longer closed, it is must be. its 99.9% closed.
8: someone fiddled the idle duty cycle speed bleed screw on top of the Throttle body, (black cap plastic under it) and its was set way off , so bad
the ISC can not get 800 rpm.
9: the ISC might have its range limited, it still works but it can open all the way or close all the way, so fails. clean it.
TESTS:
im sure if you unplug the ISC it will stop the surge. (electr, connector (has lock lever dont force it , suz, dont sell em)
what is RPM now? hot?
then pinch the ISC air line.
what is RPM now.?
put back the connector
what is RPM now, still pinched? hot.
this test tells me the total air flow , natural, and a cause of wrong.
here are all the air paths,
on a hot engine the IAC is 100% closed.
The throttle valve the same.
so the only air supply is ISC and the bleed, if not?, it will surge, or freeze a the wrong RPM..
all air is metered, if not? , it goes lean, when not in closed loop.
im glad its a 16v its Throttle body is simple, unlike the horrid complex 8v TB., that love to leak in very odd ways.
if you screw in the bleed screw 100% and the engine races way over 800 RPM , you do have air leaks, One more test, pass or fail.
even injector base cushions can leak.
mine had a cracked, main huge air intake tube (near #3 in photo), (all aluminum) the back rear alum. base mount was broken, and it sucked in air right there, at the break. took mirror to see it, on car.
as the leaks add up,, it exceeds the authority of the ISC and can hunt.
you can change the Autority rage (called dutycycle) with the bleed.
in fact screwing in the bleed can hide small leaks.
or unscrewing it for idle too low.
the bleed is actually set in the factory for 50% duty, it can increase and decrease RPM equally, by 50% . say 400 RPM to 1200 RPm (crude guess, as there is no spec on this)
if your car was new.and you have a leak of air , more the 400 rpm worth, the ISC might surge, because, it cant attain, at least 850 RPM. if it can't some ECUs surge.
one guy said mine never surges, with on purpose leaks. sure...
that is because your software is different. some ECU do, others don't, ive tried many, some just rail and freeze there.. ECU waiting for ever, hoping RPM drops. to below 850.
rule 1: hot engine.
metered air leaks cause racing (1 example is IAC stuck open or throttle stuck open) if too much, it can surge.
un-metered air leaks causes lean, an surging. ( say a crack in any tube or hose.)
be glad car is not throttle by wire, omg. complex.
unmetered air is air the MAF can't see, the maf is the Air meter. (mass air)
i need RPM range first. surge range so i can point more directly.
if car was 1996 and above. we can check for closed loop at idle to see if AFR is right. but no scan tool here.
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