Idle hunting - 1990 Ford Ranger SuperCab

this is a USA form and we dont have Balenos,
but do have lots of G16b (16valves)
that is called hot idle speed hut, its a software bug, in the ECU.
this same bug cost toyota 2bill bucks in fines. but not suzuki nobody cares. on them.
a barn find car, done many, too many.
That sure can be many things but in order its clear.
THE ISC is failing , in fact its doing the hunting, if you unplug its 2wires, it stops hunting.
the cause is really air leaks, the ECU is programmed to hold hot idle at 800, rpm , if it cant. it ILLEGALLY hunts it.
a lreal car, would just send the valve closed command over and over and not hunt it, as hunting can kill, drivers with bad skills.
First car i saw this on was a 91, Vitrara, Sidekick. G16a.
then a 96 G16b,
you have a vacuum leak.
that is the cause.
and I bet lots more ... for sure, last one like that I did had 15 majors.

"Hunting" at idle often indicates a vacuum leak. Check all the small hoses and see if any have come off.

HOT ENGINE? (ill guess hot)
idle surges.(hunts) (very simple reasons or very hard to find.
the car has 2 engines. G16A and G16B
they work totally opposite, (8valve and 16v)
the vin number tells you the engine type ,digit 8 is engine code
6= G16B 16v
U= G16A 8v
i have factory book. its in chapter 0 these facts.
the cause of idle surge and hunt are:
1: ISC failures. the ISC can stick partially open and then hunts.
clean it and test it . see videos of how.
2: engine running so bad the ISC can nOT regulate idle speeds.

#2 is caused by up to 50 reasons.
8v , air leaks, cause racing idle and iSC goes nuts.
16v , all air leaks cause lean and if too lean the ISC goes nuts.

by nuts , i mean it hunts or gives up.

the list is endless, but the tests are basic,
i cant help you because no engine stated.

http://www.fixkick.com/IDLE-AIR/idle-index-home.html


ISC = IDLES SPEED CONTROLER (a system not just a PART)

no engine type stated, there are 6 engines used.
but bad idle is caused by 2 things.

• misfire.
• or lean AFR, lean fuel mix.. causes HUNTING

the ECU can also cause the hunt if it can not hold hot idle to spec.
most cars is 800rpm.

hunting or surging ilde. name the 2 RPMS, low and high , is it hot or cold engine this issue.? 400rpm or 1000 or 2000 all are diff.causes.
no year, stated. so cant help.
but ill answer in the generic,
1: the ECU (got a carb,? )
the ecu controls idle speed at all times.
if not , there is a problem (you)
A: air leaks in the induction will make motor race at some point the ECU/ISC loses control. and hunts. trying hard to correct it.
b: egr stuck open idle too low, iSC cant correct it,, bad EGR.
c: engine EFI running way too leak starving for fuel so it hunts for 2 reasons < ISC hunting, and lean does that.
lean is gross power loss and opening throttle bogs the engine.
so is double bad. ISC makes it worse,

all this breaks down to 2 reasons.
1: ISC bad. in some way (gummed up. or restricted inside)
2: bad fueling or air leaks. vacuum leaks.

try answers , the hot cold question and the 2 speeds, of the hunt.
lowest rpm and highest of the hunted range of RPM.

CHECK THE TEMPERATURE AND OXYGEN SENSOR

clean the MAF sensor with carb cleaner if you have one in the big air intake hose. Small heated wires inside. Causes lean mixture

check the ohm rating on all plug wires. They average 28,000 ohms per foot. Of course a bad spark plug can be at fault to. These two items will cause your tack to fluctuate or hunt while idling

If the RPM's fluxuates at an idle at all times you have a bad spark plug or a bad spark plug wire

does throttle sensor check out correctly???