Idle issues

[Junglekat90]

I built a stroker out of a 96 cherokee 4.0. It is all wired up and cranks. The motor does not want to idle. It starts with the throttle slightly open but as soon as you let off it dies. There has been a few times where it will run for a 10-20 seconds by itself at around 1200 rpm but then dies. I have checked all vac lines for leaks, checked all the grounds, changed the iac still no help. One note I am not running a fuel pressure regulator Im not sure if that could be the cause of this. Ive been trying to fix this for weeks now and nothing seems to be working. Any suggestions?

[SilverXJ]

If you aren't running a fuel pressure regulator, what is the fuel pressure on the rail? ~80psi?

[Cheromaniac]

I built a stroker out of a 96 cherokee 4.0. It is all wired up and cranks. The motor does not want to idle. It starts with the throttle slightly open but as soon as you let off it dies. There has been a few times where it will run for a 10-20 seconds by itself at around 1200 rpm but then dies. I have checked all vac lines for leaks, checked all the grounds, changed the iac still no help. One note I am not running a fuel pressure regulator Im not sure if that could be the cause of this. Ive been trying to fix this for weeks now and nothing seems to be working. Any suggestions?

Since yours is a '96 model the fuel pressure regulator is part of the fuel pump/sender assembly that's in the tank, and your fuel system is returnless.
Check the fuel pressure at the Schrader valve and see if it begins to drop before the engine dies.

[Junglekat90]

I have a regulator now installed and I still cant get it to idle. Me and my Dad are running out of ideas to what could be wrong. There are no vacuum leaks, the TPS is new, IAC is new, cam position sensor is new, crank position sensor is new. One thing holding us back is the gauge for the regulator hasnt come in yet but we have tried adjusting it with 1/4 turns in every direction and still cant get it. We are beginning to think that there is something wrong with the computer. Can this be possible?

[jeepxj3]

So if you hold the TB slightly open, it will idle fine and not die?

If so, you can adjust the TB to slightly open or drill a hole in the TB plate to let more air in.
Is your PCV elbow clogged or open/passing air and connected to the intake manifold?

Post a picture of your fuel rail and the fuel line connections.

[SilverXJ]

Yes, if it is idling by cracking the throttle then you don't have enough air bleed in the throttle body. You can crack the plate open a bit more with the set screw to allow a bit more air past. Or drill a hole in the throttle plate. Start with a 1/16" and see if that helps.

[Junglekat90]

I have tried to leave the throttle plate open and it idles around 2000-2300 rpm. when i try and close it some to bring the idle down it wants to stall out. I bought a new ecm and am going to try that before i drill any holes in the throttle plate.

[Junglekat90]

New ecm didnt change anything. fuel pressure sitting at 45. Worked up to a 1/4in hole in the throttle plate and it stays running but around 2000-2300 rpm. Does the computer need to be reprogrammed since the stroker will be putting out more horsepower/torque?

[jeepxj3]

New ecm didnt change anything. fuel pressure sitting at 45. Worked up to a 1/4in hole in the throttle plate and it stays running but around 2000-2300 rpm. Does the computer need to be reprogrammed since the stroker will be putting out more horsepower/torque?

1/4" hole and 2000-2300 rpm, you have something else going on. Vacuum leak somewhere. Elbow to MAP sensor? Any codes?

[SilverXJ]

1/4" is too big. 1/8" Should have been enough. What camshaft are you running?