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rough idle shunting

coleb

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hey there i have a 1994 vr 5L with an idling problem. its got a sort of a miss but dont brake down when i rev it. when im driving it shunts at low revs when im going 60 km at about 1500 rpm and at 100 km at about 1800 rpm. iv replaced spark plugs leads fuel pessure reg most vack hoses (map sensore etc..) iv had it on a scan tool no codes only sus thing is that at idle the oxygen sensore reads rich all the time and then when i bring the revs up it starts working fine (rich lean rich lean etc..). not much mods just a 192 kw chip that bumped my rev limit up 1000 more revs it was tested befor i used it and worked good. iv had carby cleaner out looking for vac leeks but found none. its been realy buging me so if neone can help would be great thanx
 

coleb

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sorry one more thing it is back firing in second when i plunt it then let the revs kum down most time thanx
 

db_notso

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EFI EARTH CAN WORK ITS WAY LOOSE BEHIND THE DRIVERS KICK PANEL
but miss would be random... OR no start and no injector pulse

if you have acess to a data display tool then check if at idle you loose any signals e.g. crank (mainly), ignition signal blah blah balh

at idle what exactly do you mean " sort of miss"
 

coleb

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um its hard to exsplane its like a very mild lumpy cam. but deff dont have cam upgrade yet.
 

db_notso

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revs going high and low?

has it idled high low since anything was swapped or changed or modified?

fuelpressure steady at idle?

does it rev high low if you hold the revs up with accelorator in one position say 15oorpm?

air flow sensor maybe..
or the metering of fuel, pressure reg leaking into vac hose
failing 02 sensors (unplug them and it sets to a default measurement of rich)

could be a number of things like a vacum leak in fuel evap system
or any system using vacum heater hose brake booster
 

coleb

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the revs only drop dont go high and you feel it thru the car.
i dont have a air flow sensor.
fuel pressure reg is new i replaced it.
iv looked evry were with carby cleaner for vac leeks.
but could be in brake booster or in fuel evap mabe. is there a way to check them?
ill cheak the oxygen sensor to moro.what will it run like if i unplug the sensor?
and yes it duz rev funny when i bring the revs up to about 1500 rpm.its hard to get it to do it tho needs to be right in the right revs.
 

db_notso

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but could be in brake booster or in fuel evap mabe. is there a way to check them?
block off the vacum hose to it at idle and see if changes

ill cheak the oxygen sensor to moro.what will it run like if i unplug the sensor?
lower power engine light on but a useful tool to confirm its fuel meauring related
some people will even buff old 02 sensors (lightly) to make them read better
02 sensors have two types and different lifespans
a heated 02 sensors lasts about 160,000km's a non heated lasts about 100,000km's
there are some different opinions on how long they last but normally if there buggered will only affect car at idle and at cruise (highway light throttle)
OR they set a code adn engine light on

yes it duz rev funny when i bring the revs up to about 1500 rpm.its hard to get it to do it tho needs to be right in the right revs
this indicates it is a problem with maintaining a steady measurement of wither air or fuel
soz i get jumbled with models sometimes do you have a map sensor
 

Michelson4301

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What is your idle vacuum doing. Common these days that the cam lobes have worn off the shaft.
 

coleb

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yea have map sensor. i had the car on a scaner at work and the oxygen sensor stayed on rich in till i brang the revs up then it started to fluctuate from rich to lean is this what thay do? i thort thay fluctuated all the time.

hey michelson4301. i havint checket idle vacuum. how would i go about checking that
 

db_notso

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yes they are supposed to go rich lean at a steady non idle rpm

you would need a vacum gauge to check that
then check if it maintains a steady vacum which it wont if revs are constantly dropping lower
and i dont think it would explain the fault at only certain rpms and speed of car unless it at heavy vacum e.g. as stated idle and cruise (partial throttle)

but this fault would affect the map sensor reading as it measures vacum to determine throttle position (basically)
would still lean towards trying a wreckers map sensor...
they are piezio electric (spelling meh who cares) and wear out over long period of use

if not this i would lean towards a sticking injector or blocked fuel filter possibly but rae to affect only certain amounts of load (throttle )
 
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