COLD only minor stutter.!
is really called MISFIRE, not argumentative, but only to be clear what is HAPPENING, ( is weak combustion for sure)
it is 1 of 2 things,
misfire spark
gross fueling issues.
its not the iSC< for sure, your engine has EFI and This EFI mixes fuel correctly regardless of ISC positions. this is a fact.
the reason it does, is for one more fact, ISC used MAF metered air, so , mixes fuel based on that metering of air. (primary)
This ISC never shuts off ever, (off idle it goes to 50% duty cycle or to a stored value base on ECT temps, that is now guessing your next shift point
keep in mind the 5speed, you are shifting and don't want the engine to stall , between shifts. the ISC does that. and is very DYNAMIC.
It not only does that but also adds extra air, as you cut the throttle , preventing passenger neck snap syndrome. (called the dash pot effect in the FSM book)
but has noting to do with misfire. at all.
stutter, is usually misfire and is bad spark.
but in this case, id say spark is ok, ? (on a limb)
but what about fueling, ?
16v has vast numbers of way to mess up fueling. not one is iSC related. (unless the hose to it, is leaking illegal air , hose cracks.)
fuel pressure, right
injectors not leaking
no air leaks, in the induction.
engine ECT sensor reads way too low for reality and as a direct results it over fuels and runs to rich cold and has over rich misfire (black tips of spark plugs)
its not the TPS , you proved that.
but if the TPS is calibrated wrong, it IS it. but is not because you said, it stutters at other throttle angles. moving fast.
best is to think of this in pure physics, (always works)
1: did the spark plugs misfire.
2: or did the air fuel mix go wrong (injection rates wrong) you do know that if the rates are too high it causes , plugs to misfire due to plug fouling.
just 2 causes. to find it is use added propane.
there are 2 tests, , add fuel or subtract fuel.
you can cause a vacuum leak driving, and prove that test. (if this leak,(its leaner now) helps then its over fueling.
you can add propane. showing that extra fuel helps or makes it worse or does nothing.
find this cause on cars with no scan tool is very hard.
you must work blind. (if you had a scan tool you'd see what LTFT is doing.) a key clue. and would see the effects of TPS to injector pulse widths.
id leave the ISC alone, if the screws are stuck , (ccw , 100 inch lbs, do they move, yes, good, no , stop do nothing.) and is barking up wrong tree.
fuel pressure as spec, at misfire? (a dynamic test) the FPreg passes all 4 tests ( keyon, idle and WOT tested pressure (low vacuum?)
if the FPreg fails, the fuel pressure will be wrong every time you advance the throttle.
when you do that, plenum vacuum drops and the fuel pressure rises, greatly. (on purpose)
the PFReg runs that show. all of that.
the injector must have more pressure, because it is fighting the atmospheric pressure (wot caused). see?
at high vacuum the injector will over squirt (flow) due to the low pressure there. so the FPreg drops pressures at high vaccum points.
it works totally unlike any 8v TBI.
the injectors must not leak, (leak down test passes)
the ECT must not be bad.
AIR has nothing to do with this, you are. after all. ramming open the throttle with the right foot and air is near max then.,( a rush)
the EFI measures that RUSH of air (02 is off line now) and matches air , with perfect fueling, (its job 1 after spark)
its not the IAT, its only a fine trim thing, and 92 dont even have one, so its not important like the 8v is.
A weak MAF?
now i say it another way, (fueling)
are the INPuts wrong to ECU ,then that is the problem. fuel pressure is a #1 indirect ECU input (the ecu ASSUMES the PFReg is working)
or are the injector fueling wrong. (ECU outputs)
bad inputs or outputs.??
tricks of trade. all covered in ASE Classes.
how to play with fueling (blinded with no scan too)
1: unplug the evap hose, at front edges of plenum , then run a new hose to the cab plugged up, then drive and with car Stutters, (misfires) unplug this line. (engine goes leaner)
2: run same hose to propane tank nozzle (removed) at same point crack the valve (adds fuel)
3: (FPREG lies) you can run a new vacuum hose to the PFREG in a loop with a valve there an air valve. (lots of tricks here could try this:
a: try closing said valve.
b: add a T fitting to the PFREG line side, and the vacauum hand pump. now you can see dynamic vacuum with valve open. (what is vacuum now, its 19")
so you accelerate, and vacuum drops so say 10 inches. so you close the valve and try for MISfire and then pump up different PFREG vacuums.
you can try 0 to 29 inches, of vacuum to the FPreg, this will cause a 1:1 change in fuel pressure.
so say all injectors are partially clogged, you lean that the engine wants more fuel pressure to run right
or the opposite.
see my points, you can change the rules and pressures.
one more point, the engine is really 4 engines
what if saw misfire and pulled spark plug 3 and it had green antifreeze on it, all the above are just my guessing.
or the spark well was full of oil.
i pull plugs at the drop of a hat. i read them , i try to find evidence of misfire. many times its right there, trying to tell you, help.
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