Rebuilt ECU, now low idle

[Beanbo92]

Short story, got my 92, geo tracker, 3sp auto, 8v, 4x4 about 3 years ago. In the 3 years iv done new timing procedure to fix the worn shaft cog per fixkick and has be great since. Recently I've developed a shudder under load, new plugs (gapped to .028) and wires about a year ago. All research lead me to the ECU, took it out and found out it was for a manual transmission. Got the right rebuilt ECU
From a FB group member. The shudder I found out was from a broken plug wire, fixed it. Put rebuilt ecu in, now (cold start) I have to keep my foot on the gas for less then a minute or it will cut out. After that minute is idles like normal at 750rpm. Could this be a problem with the ecu? 
Tried to keep it short but wanted to give as much info as possible.

[fixkick]

Short story, got my 92, geo tracker, 3sp auto, 8v, 4x4 about 3 years ago. In the 3 years iv done new timing procedure to fix the worn shaft cog per fixkick and has be great since. Recently I've developed a shudder under load, new plugs (gapped to .028) and wires about a year ago. All research lead me to the ECU, took it out and found out it was for a manual transmission. Got the right rebuilt ECU
From a FB group member. The shudder I found out was from a broken plug wire, fixed it. Put rebuilt ecu in, now (cold start) I have to keep my foot on the gas for less then a minute or it will cut out. After that minute is idles like normal at 750rpm. Could this be a problem with the ecu? 
Tried to keep it short but wanted to give as much info as possible.

cars are complex so problems go deep and long all that is normal for SURE 28 year old  cars,  very few even run at all now.
the MT ECU runs ok but TCC lockup overdrive is dead 3sp is hyramatic so only TCC is electric.,  so does the old ECU MT run ok? now?
you have 2 ECU so you can answer your own question there.

the ECU must work and operate the dashpot,  started up, the DP runs for 5 to 15 seconde cold started and retracts, does it?  2 person test, one at key one looking DP vacuum dealybob on rear of TB.  it is engaged,  key off, it holds the TV valve open  no started and for up to 15 seconds after.  that is your 1st air supply.
the 2nd air supply (of  4) is the iAC is wide open in the base of the TB this gives you 1500RPM  cold, near.  if dead , this IAC therm wax device then you the human
gets to be the IAC, ECU does nothing to the IAC<  3 on the list is hot idle iSC but only if it sticks open cold and is not your issue, and the air bleed screw.from center of TB air horn it is, you hood up fact it and it is dead center, most have plastic cap this is hot IDLE ISC duty cycle settings, (calibr) at 50% but does give some cold air cold start,  (seen some cars person with vacuum leaks , screwed the bleed closed, then later cured (hoses bad) not the bleed is set wrong.
monkey rigged.

Refurbs on this ECU is mostly caps, most parts in side are not made now. (cept caps and resistors) so super hard to fix other than caps.
I can do transistors subs but the hybrid chips are unobtainable status.
having a spare ECU on any near 3 decade car is  prime idea.  (I'd keep the MT sure would and beats a tow home say 100 miles deep in the woods.

The ecu controls ISC and DP,   that is it for RPM
and then spark advance, is the DLC number pins empty?  must be.
extra air also can be stuck in limp home, is new ECU showing 12 codes for normal this is first.  always.
in in limphome, it will flood and throttle foot adding air is the only cure,( fake cure, that is band-aid)  limphome is the #1 cause of many  of these cars getting near 15mpg,  horrid mileage and glowing red CAT, and then it melts.  code 12, a must, is it?

DTC=12 good. all others bad.

[Beanbo92]

The mt ecu did run ok. I jumped the wires yesterday with a/t ecu and code 12 popped up.

[fixkick]

The mt ecu did run ok. I jumped the wires yesterday with a/t ecu and code 12 popped up.

does the DP work,  dash pot,  (aka. cold start fast idle device,  it must be extended (has a hidden internal springt_) that holds the trottle valve (TV ) open
even parked key on pock and even cranking and even for 15 seconds first started up.
the ECU runs that thing, via a VSV valve.
this is first.  this device, if dead the engine wants to flood, and foul spark plugs started.

the using foot, you said, well how much foot is that 1/2 or full throttle. as the later mode , causes CUT FULL mode, aka,  clear flooding mode.
or just after it starts only is the problem and  needs right foot,. action.  but if yes, that, then how long, is that, 1 seconds or  minutes/?  need to know all those details to know whats up.
sure seems like bad ECU,  the MT runs the engine the same way as the A/T.
but that assumes the wiring from the shift lever on the 3sp makes it to the ECU, as there AT start wire there, no MT harness has that.
the A/T psu, knows the car is in park and when set to drive, on the stick lever, goes to aggressive idle mode that no MT made can do.
but lets start at the DP.

its on the left ide rear here.right now on the bench it is holding the throttle TV open,  in fact if operated on hot engine rpm is 2500 just it, but that is only test.
2500 rpm calib, is the top with painted screw here, not the black plastic CAPPED no touch screw below.
I cant see your car nor see what is missing and for sure if this thing  is dead, or jerry rigged. in some way , seen on many super old cars.
the ECU controls this 100% nothing else. it must work.
one test on this old TB, is injector leak test, see it spray hot running, (top horn pipe off) and then cut the key, off, 2 persons again, and see if the injector cuts all  fuel  key off in INSTANTLY, key off,  it must. or engine will want to flood next start, this is  all normal tests on all FI cars and lots and lots more tests.
good code 12, means no shorted or dead sensors. not that they work right ever just NOT DEAD.
TB rear view.

[fixkick]

IAC is bottom thing with water hose and welsh plug.
ISC is top things with 2 pin connector (ECU runs idle hot, all the time)
injector O-ring pair not cracked, wow 28 years is 2nd wonder of the world not, really, see leak test above.

[fixkick]

IAC is bottom thing with water hose and welsh plug.
ISC is top things with 2 pin connector (ECU runs idle hot,  all the time)
injector O-ring pair not cracked, wow 28 years is  2nd wonder of the world not, really, see leak test above.

elaboration on this car this ECU and old EFI systems brick dumb they are.(then back to 1988 cars ECU are dumb and slow CPU and is why it is dumb that 1 thing)
transmissions aside, spark aside , carbon core spark wires are junk, get mag core wires for  even stronger spark.
spark timing not off,  150,000 mile slipped timing cam belt no changed at 60k per the book and the book does not lie,  as did it tell you spark wires at 60k for carbon crap.
one more given: compression is at 160psi not 50. cat not metal (if engine has full power cat is not melted)
if you think 40HP is full power it is not,80HP is. (only driving a good Sidekick answers this)8v

just EFI.  (topic)
think of ECU as 3 or 4 ECU's it is really they are called major modes.

1: cranking, is a very special mode,  due to VACUUM huge nasty bouncing actions, the MAP sensor is useless. here,  and is prime sensor here. but no now.
that means that the air supply now is UNKNOWN,  so is fixed in memory of the ECU. it knows the air supply is fixed by 3 devices, and ASSUMES that. (addition)
If the air is missing it must flood (or goes horrible rich) and wants to STALL, no engine runs lacking air (oxygen)
2:then when the crank shaft hits about 300 RPM the ECU detects (OMG) Im running now, and the MAP goes ONLINE. ( it waits for stable vacuum + rpm)

if the MAP sees no air supply (crazy high vacuum is that) it too will get lost,  setting very very very tiny injections and lean and stalls. 

3:then there is hot RUN mode and #4:last acceleration mode hot and cold. all very very different and can be thought of as 4 ECUs.  for clear diagnose.

so if hard to crank and start look for air missing.
if after start 1500 RPM is missing ISC dead, this will never end.


the IAC can be tested in hot pan of water at 180f as it opens at 150f (starts) and opens fully at 180f and must, or starting will never ever be fun.
the IAC has wax pellet inside, just like water thermostat has,
but lasts longer that 10 years,  of the latter, after 20 years of 20,000 thermal cycles it dies. most would be 40,000 cycles 4 trips a day .
as many things do. even that old DP.

1 question are spark plugs wanting to foul out, with carbon? or  green  antifreeze  or soaked in raw gas?) spark plug reading tests, worked in 1900 year to 2020. all valid, but not lead fouled that is gone. just that.  

now monkey rigged cars:
seem these vast times
car run in limphome for 5 years, or worse  backup mode
the PO a monkey , does evil things,  not fixing true cause, but tries to hide it by messing with all screws marked do not touch. (all 3 of them)
one more on a 16valve G16 we saw a guy that jammed bamboo slivers inside the FPR, valve,  to raise fuel pressure over spec to hid clogged injectors. wow, that was hard to prove but a fuel pressure gauge,yah did.

yah, stuff like that, is crazy common on old cars for sure 28 years old. seen every dirty trick in the book me, but love to see more, love to  crazy stuff, for fun.

wars are won by doing monkey rigs (jerry rigs)  and I like to see what they did.  Bailing wire, Sealing wax and the like.
not saying yours is, ok, just to be aware of it and the CEL lamp removed bull.   like that.
we already see wrong ECU, so we know the PO was , as they say a fancy dancer. " walk on the wild side"?

cheers and good luck, my topic today, lost AIR.

[Beanbo92]

The cold start procedure as of now is, crank car, idle goes to 1200 rpm for 2 secs then goes straight down to about 550-500. I hardly keep my foot on pedal to keep it at 1000 for no more then 45 seconds after that is goes to 800 and idles like normal. If I don't keep foot on gas it will cut off. I did replace the cat not long ago and the old one seemed to be fine not clogged. I'm trying to upload images from my phone but files are to large. The black cap is still on the bolt is the white painted screw on the other side of the black cap screw.

It's been pouring off and on here in sc, trying to diagnose between rain periods. I do appreciate all the help very much.

[Beanbo92]

I'm assuming the dashpot isnt working due to not high idle for 15 secs. But il try and get someone over so I can do the 2 person test. When the m/t ecu was in it would crank up idle to say 1500 or so stay there for 15-20 secs then go slowly go down to normal idle.

[fixkick]

I'm assuming the dashpot isnt working due to not high idle for 15 secs.
But il try and get someone over so I can do the 2 person test. When the m/t ecu was in it would crank up idle to say 1500 or so stay there for 15-20 secs then go slowly go down to normal idle.

the DP lasts from 5-15seconds all ECU math on coolant temps (ECT sensed).  colder the engine the longer the fast idle,  for this short run device, (seconds)
the IAC is 100% thermal device, and takes a long time to get 150F water temp.   this device is not ECU controlled at all, it is pure thermal device , in the the base of the TB,  a cold engine this device if open letting in air ,  for about 1500 RPM cold idle.  (active for a long time.  lets say the water temp is 60F and you start the engine, and the engine warms up, the IAC closes at 150F and for sure 180F (thermostat does the 180F regulation)
the 1500 rpm walks down to a point that the ISC (electric) takes over. at 800rpm. +-50rpm (750 to 850Rpm is spec hot RPM all ISC controlled (+ECU runs this device)
that is how it works.
if the MT can not run the DP, the the transistor is bad in the MT, tha DOES THAT.  (isc DRIVER) TRANSISTOR Q100 RUNS THE ISC IF ISC IS DEAD, and not jammed with gunk as most are this old, the Q100 is bad.
https://fixkick.com/ECU/transistors.html

this is my transistor bad page on the 56Bxx series ECU (usa only)

you skipped test #1 , the ONE PERSOn test.
1: open hood. key in pocket, engine off.
2: look at DP plunger it holds the TV open, with its plunger rod, it holds it open say 0.016" they all do this parked, and stays like that for up to 15 seconds started..
look closely, or use vacuum tool test the diaphragm in the DP, make sure it even works at all.  do the diaphragm leak down test, we do to all diaphragm vacuum devices on all cars.  (cold start fast idle device, DP, is extended by default , key off)

learn that fixing one problem of 5 can un mask other problems.  (one hides the other, is very very common on any car with EFI 28 years old)
on newer cars OBD2 tests are not even done until lower order failures (DTC) are cured first. so are even more complex. (hiding rule)
The next test and next device is MR. IAC, it is #1 device, of cold start air supply and cold idle.  
can 2 wrongs make a right,, sure can in electronics, (casual looking) if the ISC is bad and stuck open you dont know the BAD IAC is there, see?
or old ECU has bad ISC port hiding the fact that the IAC is dead. 2 wrongs = right.  see?   life is full of surprises, looking deeper, (peeling the onion)
what will be , will be....

iAC tests....

the IAC is here.  inside the TB throttle body. " Idle AIR controller" thermal,, (look ma' no ECU)
it is open at all times cold. cold water.   the colder it gets the more open it is, and at 150F it closed and stays closed up to 180F
all data below is MINE this is my work to learn what it does, with a way to measure the distance (#60 drill set shanks used)
using 3 tests cases.  a refrigerator 40f (next to milk ) and -10F freeze (next to steak) and hot water pan, on stove. tests.  I did 3 tests.
the gaps are learned using number drills as feeler gauge. see? checked on 2 cars that ran 100% perfect and no failures  of any kind.


SUzuki has no dreams of this lasting 3 decades, 10 maybe, 20 with luck but 30?
[img] https://fixkick.com/sensors/sensor-icons...ermo1w.jpg[/img]


maybe the other MT ecu has failures too, that hide other failures, like DP and ISC.
we use tools to learn this, it is not ever easy, lacking new spare parts,  used parts can be bad.  there are no new ECU now. zero.
we test the DP at its VSV for proper operation, then check IAC is open, one can blow air in to its air ports and see if they flow air cold.
sure can.


the IAC sucks here from here.
all do. cold,,  we learned all this buying used parts bad,  then we learn to test that on all used parts and if good , we win. (used parts must be tested)
 

the other hole that sucks air for IAC is here (in my slide show TB) as you can see this is harder to do air horn and upper body of TB removed



IAC can fail stuck open or closed,  many do stick open and hot RPM is like 3000 RPM or more.  lots do after 3 decades. if not now soon.
all FALSE leaks cause too fast idle not too low like yours.

TV = throttle valve of fly plate as in Butterfly plate (engineering term latter)

the bottom photo AIR port IAC is for IAC and the bleed air screw, both, so I close the bleed screw counting turns till closed writing that down on paper and then test for air flown in hand, (lips to port) cleaned,  the later put the bleed screw back, to its correct setting, (factory)
the air bleed screw is here this is ISC calibration screw for 50% setting.,.  




this topic is about lack of start up and cold idle air supply.  all cars made now do this, same thing using similar devices, ISC for sure)
most cars use  single valve now, that runs hot and cold air supply (idle air) and is smarter and faster and has no need for this IAC thing nor bleed screw.
the smarted cars (ECU) alto calibrate the TPS, and ISC,  look ma' no screws to fiddle, on new cars and no spark timing either, fixed.
this is the dark ages of ECU, old slow dumb and the mech needs to be smarter  and work harder to solve problems, in fact most shops will refuse to work on cars this old. due to all the above.

good luck find what is wrong.
PS:
Most these cars this old , in 1 hours of labor and testing is see 5 things wrong, some can be very hard to cure lacking SUzuki parts,  many are not sold now. new.
at all.
Suzuki went bankrupt here and in canada. log ago, do not sell cars a all here. USA.
Toyota parts do not fit, not these key parts.

is your ecu refurb , from ebay or top car store from CARDONE 1,  rebuilt the latter is prime the former is a joke.

some fleabay sellers think a refurb is dust off.  they grab it dust it off and sell it as  refurb, ( BS)

[fixkick]

or as some would say what is NOT Bad now.?
30 years of wear and tear.
what is not bad is the real question.
We only see 1 of these cars on the road here per year, just 1, and my wife says, look there, a GEO cracker, (her cute name for it) Saw one Jan 2020. 2dr, ratty.

takes air to run an engine, all EFI cars have resources to supply that, and driver is just holding the key.