97 stick or automatic.2wd, or 4wd? the 97s in N.america are all 16v MPI engines.
the cat clogs, no WOT full power. not possible there.
so cat is OK;
and the brick inside is there, or p0400 full time...
the erratic idle is key here, most simple to diagnose, for sure with scan tool data. live
its misfiring to drop below, 800. did it? and that 1200 is surge with foot off throttle.
idle misfire, (tool lean or too rich it must be as it does this)
if it happens as coming to stop sign, we usually those pesky EGR main sticking as the EGR closes just 1second before a stop.
and can stick there.
but will never cause 1200 rpm.
nor the bogging, how can a bogging engine do 1200 via ISC , it cant. (why would it go to 1200. my guess, is metered air leaks or unmetered leaks on a gross rich engine.)
are all vacuum hoses ok? not cracked for fell off.
is the main air pipe, sealed up end to end from TB to MAF, any leaks here are lean causing. (all metered air leaks cause racing)
the old spark plugs were black, id hate to ignore this very good evidence
seem the ECU is in limphome , or was.
or the fuel pressure is high and (bad FPR is common this old) and runs rich all the time.
if true.
then idle can hunt has it misfires. (400 >800 and repeat) not 1200.
the key is misfiring. im sure you'd feel that happen, hear, feel and see engine shake or if 5sp, feel the shifter shake hard? (its connected to engine, unlike a A/T)
but no P30x codes,. misfire (did you check pending codes for this code)?
make sure Brake booster does not leak.
the ECu can go tad nuts with leaks, it tries to correct and fails and then ISC goes nuts, it can reset and then hunt. (but never seen a 97 do that only older" a bug there")
that 121. ( driven hard this can set)
performance
i think that is driving code, it is.
it sees huge air flow, (maf) but with wrong vacuum in the plenum.
or the opposite,
basically means air flows contradict, throttle angles grossly.
FSM SHOWS:
that 121 is Incongruity between the 3 sensors. basically throttle angle is not agreeing with the map. under load, >25 gr/sec on map
pretty smart test, 3 ways, maf/map/TV angle.
my guess is the bogging engine under normal avg. load tripped 121 due to low vacuum.
when you loose power, the drive steps harder on throttle, and vacuum falls like rock.
bam 121.
or misfires, do same thing, gross loss of engine power, and vacuum drops. with throttle above 35degrees.
on different track.(no pun)
IT hesitates.
off idle or tip-in hesitation is some cases..., the TPS bad. if and only , it blogs (not misfire ) AND, it catches up (the catch up is MAF waking up)
all engines go lean, at TIP-in (that huge air slug lacks fuel)
the ecu instantly goes to enrich mode, here, if not, the TPS failed. (it is the instigator of that event (and your foot sure)
if the fuel pressure was low, WOT would fail and the maf will not cure the lean, do to lack of pressure at the injectors)
on old FPR, that sticks , can stick at any point, if it sticks open fuel pressure is low all the time.
the 16v FPR gets tortured to due to every time you move your right foot it moves with you (Vacuum) at WOT the FPR adds 6 more PSI fuel pressure (depends on altitude)
one idea is to keep watching pending codes some times, the DTC are hidden there. (marginal failures that speak loud))
i guess the key here is , bog or misfire, the cause.
are spark plugs still white?
the cat clogs, no WOT full power. not possible there.
so cat is OK;
and the brick inside is there, or p0400 full time...
the erratic idle is key here, most simple to diagnose, for sure with scan tool data. live
its misfiring to drop below, 800. did it? and that 1200 is surge with foot off throttle.
idle misfire, (tool lean or too rich it must be as it does this)
if it happens as coming to stop sign, we usually those pesky EGR main sticking as the EGR closes just 1second before a stop.
and can stick there.
but will never cause 1200 rpm.
nor the bogging, how can a bogging engine do 1200 via ISC , it cant. (why would it go to 1200. my guess, is metered air leaks or unmetered leaks on a gross rich engine.)
are all vacuum hoses ok? not cracked for fell off.
is the main air pipe, sealed up end to end from TB to MAF, any leaks here are lean causing. (all metered air leaks cause racing)
the old spark plugs were black, id hate to ignore this very good evidence
seem the ECU is in limphome , or was.
or the fuel pressure is high and (bad FPR is common this old) and runs rich all the time.
if true.
then idle can hunt has it misfires. (400 >800 and repeat) not 1200.
the key is misfiring. im sure you'd feel that happen, hear, feel and see engine shake or if 5sp, feel the shifter shake hard? (its connected to engine, unlike a A/T)
but no P30x codes,. misfire (did you check pending codes for this code)?
make sure Brake booster does not leak.
the ECu can go tad nuts with leaks, it tries to correct and fails and then ISC goes nuts, it can reset and then hunt. (but never seen a 97 do that only older" a bug there")
that 121. ( driven hard this can set)
performance
i think that is driving code, it is.
it sees huge air flow, (maf) but with wrong vacuum in the plenum.
or the opposite,
basically means air flows contradict, throttle angles grossly.
FSM SHOWS:
that 121 is Incongruity between the 3 sensors. basically throttle angle is not agreeing with the map. under load, >25 gr/sec on map
pretty smart test, 3 ways, maf/map/TV angle.
my guess is the bogging engine under normal avg. load tripped 121 due to low vacuum.
when you loose power, the drive steps harder on throttle, and vacuum falls like rock.
bam 121.
or misfires, do same thing, gross loss of engine power, and vacuum drops. with throttle above 35degrees.
on different track.(no pun)
IT hesitates.
off idle or tip-in hesitation is some cases..., the TPS bad. if and only , it blogs (not misfire ) AND, it catches up (the catch up is MAF waking up)
all engines go lean, at TIP-in (that huge air slug lacks fuel)
the ecu instantly goes to enrich mode, here, if not, the TPS failed. (it is the instigator of that event (and your foot sure)
if the fuel pressure was low, WOT would fail and the maf will not cure the lean, do to lack of pressure at the injectors)
on old FPR, that sticks , can stick at any point, if it sticks open fuel pressure is low all the time.
the 16v FPR gets tortured to due to every time you move your right foot it moves with you (Vacuum) at WOT the FPR adds 6 more PSI fuel pressure (depends on altitude)
one idea is to keep watching pending codes some times, the DTC are hidden there. (marginal failures that speak loud))
i guess the key here is , bog or misfire, the cause.
are spark plugs still white?
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