Hard Starting

OK
I have a 99 GC with the 4.0, recently it decided not to start when cold unless the gas pedal is fully depressed. Until it warms up idles around 1100 rpms. When warm idle runs around 725 and GC starts normally w/o depressing pedal. Recently replaced the AIC so i doubt it's that, any one have a solution?
Thanks

OK
I have a 99 GC with the 4.0, recently it decided not to start when cold unless the gas pedal is fully depressed. Until it warms up idles around 1100 rpms. When warm idle runs around 725 and GC starts normally w/o depressing pedal. Recently replaced the AIC so i doubt it's that, any one have a solution?
Thanks

Well replace the IAC (Idle Air Control) Valve again, thats deffinately your problem.

Remember to disconnect the battery before removing/replacing the IAC along with any other electrical component on jeeps.

OK the IAC is less than 3 days old.
Was replaced B/C IAC pinion was not extending nor retracting (hard start with rough idle).
Now has no start cold except if pedal is floored, When warm(ish) starts normally
Yes the battery was removed prior to replacing IAC and left off for several hours to allow computer to reset and allowed to idle for some time to allow computer to reset/learn.
Should i start looking at the TPS?

OK the IAC is less than 3 days old.
Was replaced B/C IAC pinion was not extending nor retracting (hard start with rough idle).
Now has no start cold except if pedal is floored, When warm(ish) starts normally
Yes the battery was removed prior to replacing IAC and left off for several hours to allow computer to reset and allowed to idle for some time to allow computer to reset/learn.
Should i start looking at the TPS?

No the TPS will not effect the starting of a vehicle, irratic idle and other driving problems but not starting.

Did you adjusted the pintle according to the specs in the instructions that came with the new IAC Valve.
I know for my 94, the instructions said to adjust te pintle to 1-1/8" from the mating surface of the IAC to the very tip of the pintle. To adjust just slide and hold the inner sleeve in (it's spring loaded) while turning clockwise/counterclockwise until adjustment is made.

I don't think it's adjustable on the 99+ GC's
On the New one, the pintle doesn't appear to adjust and the box had no installation sheet.
I know what your talking about my old 87 was adjustable by screwing the pintle in and out of the IAC body.
Checked the GC shop manual and it doesn't have anything about adjustment when replacing.
I'm thinking the TPS might not be sensing throttle plate closure and is causing the IAC to fully expand blocking the air passage.

I would make sure your battery passes the load test and terminals are clean, WJ's terminals like to corode a lot. When it starts in the morning does it run rough? I have seen injector leaking down and flooding out cylinder. And of course good old fuel pump check valve o-ring. 99 is famous for that, if oring thorn bad, it lets fuel bleed down inside the tank and puts air in fuel line, it takes a while for it to work air out, so when you give it gas the injectors pulse faster helping air to come out and start. The best way to check for that is to install fuel pressure gauge and perform bled down test. Good luck

Ok
The "new" IAC was defective (that's another story) and i installed another IAC
same symptoms No start cold (at least 1/2 hour engine off) except if peddle is floored, starts fine warm but now idles rough and stalls when cold, smooths out warm. Replaced the TPS as back probing wires, voltage was off. Shop manual calls for .4 volts closed to 4.5 WOT i had .7 closed to 5.15 open. Did Fuel pressure check # were within Shop manual's #s except had slight fluctuation in needle from about 47 lbs to about 53 lbs at idle.
Any ideas where to go from here?

Sounds to me you did runing fuel pressure test, you need to perform fuel pressure bled down test, leave fuel gauge hooked up after turning the Jeep off(ign off), watch how fast the pressure bleeds down, how low does it drop in 10 minutes?

Sounds to me you did runing fuel pressure test, you need to perform fuel pressure bled down test, leave fuel gauge hooked up after turning the Jeep off(ign off), watch how fast the pressure bleeds down, how low does it drop in 10 minutes?


Gorby
Did both running and pressure bleed down (should have said that sorry).
Pressure drop @ 10 minutes was almost none (stayed about 46 lbs). After about 30 or so minutes dropped to about less than 10 lbs but still had some pressure maybe 3-4 lbs.
All within Shop manual #s and when key on w/o start immediately jumped to about 49 lbs. stayed there with slight fluctuation and engine running @ idle.

What happens to the fuel pressure after 45min? it shouldnt drop to 0, and what fuel gauge looks like after sitting for an hour and trying to start it without pushing acelerator pedal. Like i said before, make sure you have clean battery terminals and battery passes the load test. I think it's fuel pressure related and posibly one of the two, it's either fuel injector bleeding down and flooding out cylinder or like i said check valve oring inside the tank. I would unbolt fuel rail four bolts and poped it out of intake with injectors about 1in,cycled the key(without starting) and watch fuel injector ends, if one is bleeding down you'll see fuel squirtng out of end. You said it only happens 1/2 later, pressure droped to 3psi 1/2 hour later, thats low. If the injectors check ok, it's got to be fuel pump o-ring. Kit is only $20 from dealer. Try that.

OK it looks like i found the problem, I hooked a scan tool to the jeep and found that the coolant sensor was reading -15 when cold overnight. Replaced the CTS and now jeep seems to be starting w/o issue, left for several hours and overnight. Now CTS reads 87 degrees after replaced and engine cold overnight. Hopefully the problem is solved but only time will tell.
Thanks to Dksob81 and Gorby for your help.

good diagnoses. coolant temp. sens is the most likely cause. when you floor it, it sends cpu into flood mode temp. bypassing sensors causing start emp. the rough running is because cts inputs to cpu to enrichen fuel mixture.