the 8v cars are all tricky on idle.
if ecu is happy and not in (failsafe or Backup)
http://carfix.stufftoread.com/ECU/fail-safe.JPG
if it is forget idle and work the real problem.
keep this in mind on all 8v
on 8v , the Map runs the show(rare to fail) and if there is any air leak , any at all
the MAP finds it and adjusts the AFR (airfuelratio) perfectly (ecu does this really)
and the result on any 8v is a higher idle. [ and FULL POWER }
the idle is special on these old buckets.
the idle is comprised of the following factors:
1: Buttery fly plate stop screw (a factory minimum air , never to be changed)
2: IAC (bottom TB ) cold air valve (100% mechanical wax pellet) closed hot.
3: Bleed screw on front center of TB. ( idle setting hot screw)
4: ISC ( or as i call it IAC-E for electric) this functions both hot and cold.
5: illegal air leaks.
6: The Dash POt (on inside left TB ) called the Cold start air valve (30seconds of screaming it causes at cold start , hate mine)
7: and last of all YOUR right foot is the huge air leak. (but really #1 too)
the 16v is missing #6 and goes lean with leaks.
the 8v just loves air leaks.
you can climb a mountain with a good air leak ( see #7)
This car is a Speed Density system. (no MAF)
one more other factor can come to play?,
there can be sludge packed below the butterfly plate , wrecking the the calibration !
of #1 above. Ask any Ford or Jeep owner. (grin)
it prevents the plate for fully closes or simply blocks normal flow.
As you can see the air induction side is complex.
#6 is easy , if it don't retract , it is bad. easy as pie to check.
on any 8v , it is best to :
check vacuum , to see that it is steady, if it is not, the EFI will go nuts.
check hoses for leaks. (i pinch them , no idle change)
every single hose gets pinched, then is say to self, is this idle drop ok?
PCV yes, ISC (91 and newer) yes, Brake booster no, all others no.
but the MAP hose needs to be TEST physically tested, because if you pinch it you starve it from vacuum, and it ?thinks OMG, WOT (wide open throttle) (rich happens)
when I say IT, i always mean the ECU and the sensor , acting as a servo.
almost every map hose after 15 years. melts and cracks. so visual , test it.
and vacuum test it. make sure vacuum reaches the MAP (melts inside too)
keeping 15 year old vacuum hoses, is really just a waste of time and pain. IMHO.
each car can have 1 problem or more.
id check vacuum first.
a bad engine is well, a bad engine.
not knowing vacuum and compression on any badly running engine,is being blind.
cheers.
PS:
more toxic soup
if the min, air supply is not supplied in certain modes,
the ECU goes crazy (no really) and hunts the ISC.
hunts. yes, it goes HIGH , then low , then HIGH over and over
the idle. trying in vain to find the 800 rpm sweet spot.
a clogged up Dashpot ,vac. nipple will do this, as will a collapsed vac, hose to same.
we suspect there are many fail modes to cause ISC HUNT.
too many permutations of fails to test.
just inplug the ISC, if the hunting stops
you know why, right. ECU is just trying to unstick the silly
nasty ISC.
this shows a SMART ECU, is working and so is the iSC.
together.
Linear Mode
