My 97 4.0 Idle jumped to 3000rpms and won't come down?
2 causes on all jeeps.
vacuum leak big time.
or
ISC stuck open.
all leaks cause that.
really the ISC is a vacuum leak when its stuck open
so is only one cause.
the engine can not run with zero air supply.
yours has TOO much air.
there are other causes.
stuck throttle cables.
stuck open throttle valve (clean it)
all are same, vacuum leaks. all are.
also
in usa 1997 we can scan it with any scan tool
do so.
1998 in canada.
the scan tool may show what is wrong.
1: map readings wrong.
2: isc , controls dead. or wrong.
3: TPS gross errors.
if in usa, (nobody ever says) then scan it first.
on a car this old.
vacuum hose cracked,
ISC stuck
TV valve underside packed in CRAPP.
clean it.
see this gunk, it can block open the TV
and it sure will race (idle out of control = race)
http://www.fixkick.com/IDLE-AIR/Slide_Show/images/TB-bad-back.jpg
it's easy to detect this,(TV failure)
while at 3000 RPM
open hood,
put hand on TV bell crank (at cable)
push it closed, if idle drops BINGO TV GUNK city
the tool is cheap. (OBD2 scanner)
you can barrow one from any friend that is car savvy.
or rent one.
or drive to and ASE shop in USA and say
"mr idle out of control scan it." please.
but 3000 rpm is too fast to safely drive.!
so tow it , or use the tow cash saved, to buy your fist scan tool. (it pays dividends for life)
for cheap $100?
get the innova 3160, I don't sell them.
it's best bang for buck tool; usa, 96+
History of 4L, (i run V6s now) 5million 4l made.
my first 4 jeeps did this every 20k miles
until i learned the fix.
my 4L all raced.(dove the over 250 miles each)
i removed the ISC stepper motor.
and cleaned it and now it's unstuck,
there is trick to fix it, ask)
ISC = idle speed controller.
when idle is out of control, this can be it.
if you have a huge vacuum leak the ECU closes the ISC 100% and stick there, and can not close
over 100% and so idle now is out of control
all jeeps can do that. everyone, 1988 to now.
×