I have 97 4.0 xj, when cold, the engine sumbles a little and pops out of what sounds like the intake, my issue is gone when I floor the gas...usually goes away within a mile...but at full temp...if I turn it off for a few minutes...it will pop again a little for a minute or two....once in a blue moon at idle it fluctuates , but only rarely....I put on a 99 intake, mustang injectors, accell plugs cap and wires and just had the head redone with new seals...I also put on a header...conical air filter....new o2's...also ,,,I have a NSS code and I installed a new NSS...but I think someone bypassed it as if I unplug it it still operates 100%..lights starts in each gear and all...not sure where its jumped...its not at the plug areas...I see nothing on the computer on the fender...will this add to it?

Thanks!!!

 

I get the same popping noise accompanied with a stumble from time to time. If I let off of the accelerator for a second and then get back on it, the noise and power loss are gone. Interested to see what everyone thinks.

 

timing might be a little off.. it's easy to mess the timing up when putting the head back on.

 

Ummm...... No.
Only way to screw timing up would be to mess up the plug wires and that would not go away when it warms up.

 

if its popping at intake pretty sure its running lean, any cels

 

I have a CEL from the front O2 sensor. Have replaced it twice, pretty sure there is a problem on the wiring as it keeps coming back.

 

yes check wiring any defects could cause voltage to sensor issues and mislead ecm

 

the firing order and wires are straight....the only CEL code is p1899 for NSS. I was thinking vaccum leak? but where? the none used vac ports are capped off... and as far as the NSS what would a bypass look like...butt conn? thanks

 

Fuel delivery issue.

 

but its only at start up...the injectors are clean and working...and I have proper fuel pressure on the rail gauge...

 

this is driving me nuts.

 

OK now I am getting code p1302 in addition maight have been a P1320 a little dislexic..the one for the distributor....any thoughts are welcome///

 

fixed the nss , changes the ICV...nothing...no codes at all...hall effect? TPS ? but with no codes?

 

stop using Bosch o2 sensors... get NTK's in there. Bad o2 sensors CAN make your jeep run lean. also, your code sounds like a weak spark or bad Crankshaft position sensor.

 

i dont see where he mentined Bosch; but Bosch makes great parts. in fact theyre OEM parts for a LOT of different car makes. at any rate; hes on his 3rd o2 sensor with no change; its going to be a waste of time and money to replace it again.