95 geo tracker idle problems

[cmays03]

ok i have a 95 geo tracker with a 16 valve in it. I just rebuilt the motor. now i have an idle problem. it idles good for a bit then starts to studder then idles back up to normal. any ideas on what it could be.

[jtgh]

that's real hard.
the thing is, the car may be leaning out and cant idle
or
it could be flooding and fouling the plugs (tune up ever ?)
only your nose or 4/5 gas analysis will discover it
read the spark plugs.

color? is the shade tree way , crud but can find gross conditions.

is it hunting. that is the correct response of a working ISC (idle speed controller)
when the ECU tries hard to increase idle and it is starving for fuel, then the fuel catches up and the idle ISC has gone too far ,now, so it must now correct the problem
and the cycle repeats.

or it could be an air leak but that would make it lean too. as per above.

it could be abad o2 sensor.
the problem we have is that this car has no scan tool.
so we are a tad blind.
check engine light on, at key one ,no start and off after running.?

cheers

[cmays03]

no trouble codes. only code 12. new plugs wires cap rotor. timing is dead on. rpms 800. did it on the last motor also. i'm thinking a sensor. its jsut a toy so not a big deal just wanted to get some ideas from here.

[jtgh]

could just be the lack of a tune up for 60k miles or more.
there are 2 sevice points, 30k and 60k. minor and major.
most ppl ignore these.

or it could be a sticking iAC


the worse case is a bad maf, a maf that lies and says, there is too little air coming in the air horn.
ecu then mixes insufficant fuel, but the working 02 will correct for this up too 15-20%.
if the maf drops goofs up too much ,then it wins and car goes lean.
(the rules for this are no where and very by car, ecu and year)
but books say ,watch out for any sensor that goes way off track (no pun)
the O2 sensor is very crude and is only a switch.
too rich, too lean. is all it says.

[jtgh]

tricks to add fuel

pull o2 sensor elect. conn. (ignore CEL lamp)
doing this will
make car go to 13 to 14:1 ration and run great ,just a little rich.
if car goes leaner, MAF is toast.
or massive air leak.

with o2 pulled the EFI goes to the intrinsic AFR. (air fuel ratio)
the O2 is designed to Pull fuel out , of the equation for fuel.

this adds fuel , if EFI is working correctly, it may not.
im trying to think shade tree here.

one last trick is pull only the maf sensor conn elect pllug.
again, ignore CEL glaring away.
this time the EFI will mimic the MAF, using the TPS and the Map sensor and RPM.
it will do so , poorly.
but if a lean engine becomes rich, the maf may be toast.

test 2 on maf
rap it with back side of screwdriver
GM says to do this and listen if rpm (idle) rises . if it does maf is toast..
paraphrasing here.

good luck there are some things to play with.

[deeznutts77]

mine was doing that tooand i changed the iac thing "not it" and forgot i unhooked the collant line that goes into the tb "fixed it", so if you need a good iac i have one.

[cmays03]

well i have been missing with it and its blowing out some blue smoke and black smoke so thats telling me that either the rings are not seating right or something like that and that its running rich. i guess i will have to check the tps iac and a few others.

[GoGeoGo]

is the idle supposed to be around 800 rpm? mine doesn't go below 1000rpm and when it does, the engine shakes, along with the rest of the car, and the rpm bounce a round between 800 and 300 and then go back to 1000rpm

[cmays03]

yeah i idled mine down to 800 but gonna idle it back up just want to check some sensors first. gonna do that tomorrow cant work on it today.

[jtgh]

if the engine is running rich, it has issues.
if it runs rich it washes the oil off the cylinders and burns more oil and causes excessive wear on rings and cylinders.
this motor can be (ecu really) be stuck in limp home and in that mode , it purposely
runs rich and retarded, and the MPG drops to 15-20.

tune up.
check compression.
check vacuum (steady at about 19 inches HG)
then sensors.

this fools many folks, it runs , how can it be bad.
one word "limphome mode" it was designed to get you home safely , not run like that for a decade. hahahahahaha

bad engine.
bad EFI. (efi cant compensate for former (just a little) so engine must be evaluated.

if your motor shakes when you go to low in rpm ( trying to see 800 huh)
then it is sick.
motor has dead cyclinders.
motor is runing lean. (starvation)
motor is so rich it is fouling plugs. ( called loading up)

idle is the last thing that works correctly on all EFI engines.
all else must be correct first. ( says this 50 times through out FSM )

its just a symptom of something more serious.

but some get lucky clean the ISC and all is good.
cheers.