PLZZ HELP Idle problems and stalling

[mikeyost]

Please help another problem which i am stumped on, i have a 1988 jeep cherokee 4.0L manual transmission and gosh, thats pretty much the word i have to descibe the pain i'm in "gosh"

What seems to be happening is that when its "COLD" when i just start it the idle seems to be "okay" but i'll drive it for like a minute or so and as i put it in netrual the idle goes crazy..... some times it will die, and i'll have to crank it for like 15 seconds and it starts up and it seems to run okay, but the idle is still a little buncky, i have also noticed some hesitation on acceleration. its deff not the
Fuel pump
fuel filter
air filter
distibuter cap
wires
spark plugs
doubt its the fuel injectors, ive put fuel injector cleaner in it. (undertand this may not fix the injectors)
because this system is fuel injection i have no clue what this may be "DAMN COMPUTERS ARE RUNNING THE SHOW I DONT KNOW WHATS GOING ON"
plzzz help me i have never had a mechanic work on my truck since i bought it, and i ant going to start now

 

[MudderChuck]

Things that affect idle are:
O2 sensor, tries to keep the proper mix
Temp. sensor, lower left of motor, keeps idle up a while, until motor warms up, deactivates EGR until motor warm. O2 sensor, temp. sensor and knock sensor have a common wire harness, that runs down front of the motor (extension of the fuel injector harness), often gets cooked on hot parts.
Idle motor on the throttle body, tries to keep a constant idle/air fuel mix.
Vacume leaks, will make the idle high, hunt and irregular. Anything from a cracked/broken/disconnected vacume line to a bad intake gasket/sometimes the brake vaucme booster hisses and looses vacume.
EGR valve stuck open, funcky idle and stalling. You can watch the EGR function on a warm. motor by working the throttle and watching the rod move near the base of the EGR (Usually works at mid to high RPM; but not at full open throttle). Cracked diaphram (vacume leak), weak springs in EGR, idle and missing/bucking.
TPS throttle position sensor, messes up idle, sometimes high idle, also sometimes affects shifts in the transmission. MAP sensor and TPS are interelated, one messes up it affects the other.

The position of the EGR solenoid (left fender well inside edge) is normally open, the computer (temp. sensor) shuts it (supplies power, activates it) so the EGR won´t operate when the motor is cold (doesn´t work well). Try plugging the vacume line at the EGR with a 1/4" screw and take a test drive, if things improve, the problem could be the EGR, the solenoid or the temp. sensor. Stuck open/hanging or improperly seated EGR. You can sometimes get a little finger in the slots at the base of the EGR and push the diaphram a little, to get a little feel, how smooth it perates. Easy to tell if it´s sicky if you remove it and work it by hand some (will probably need a new gasket).

 

[XJNick]

Hi,

You forgot to say what model year we are talking about here.. makes a big difference in the way of the electronics.

Also, NOTE that the oxygen sensor only affects how the Jeep runs AFTER the engine has warmed up to operating temperature. Until then, the computer is stuck in an Open loop mode and ignores the 02 sensor. :mrgreen:

-Nick :!:

 

[graewulf]

I assume from your list of "it's definitely not these" means that you replaced all of these parts recently, not just looked at them (all except the fuel pump, this is the only part you listed that you can actually test). Especially the ignition parts, you can't properly test these, all you can do is replace and see if it makes it better. often problems are not visually apparent. if you actually let it warm up before putting it in gear, does it stall/behave any differently before warming up? It is possiblte that the choke is sticking closed, try stomping on it to open the choke up and/or moving it by hand. idle motor/tps would be my guess if the rest are working properly.