2003 3.7L - RPM drop when throttling

tester

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Started having a problem where it would lose RPM (gradually drops down to around 1000) and get shudders even though my foot was on the throttle. If I let go of the throttle for a few seconds and then re-press, it would have some power, or if I press the throttle harder. I replaced a dead fuel pump+filter (this was happening before that), a coil pack that the coolant bottle was leaking on (along with the bottle), IAC and TPS. No codes have popped up.

Jeep idles fine, and drives normal for the first 2-3 min, and then all of the above starts happening. Would anyone have any idea what this might be?
 
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tester

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Is it possible that O2 sensors could cause this? I would think it would throw a code (although its probably a good idea to change them out anyway since I dont know when the last time they were changed, if ever).

Im going to try and get it to do it in the drive way tomorrow, that will atleast be a bit easier to diagnose instead of driving it.
 

Artart

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I would rather look at the fuel pump first. That's fuel pump overheating symptoms. Next it's going to cut out when driving. Following. Pump not pushing enough fuel now there is air bubbles in the fuel line causing the shudder. Idle smooth because you basically just need fumes to idle. Most people would say check the sensors first but I would put my money on the fuel pump. Also check for fuel leak.
 

LibertyTC

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Did you buy a Mopar IAC or an after market? & did you clean the port inside of the IAC with throttle body cleaner?
Yes test the fuel pressure.. ignition on-psi reading- running psi and key off for 15 minutes psi reading is?
Rich Condition, See this link: https://www.700r4transmissionhq.com/p0172-jeep-liberty/
 

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tester

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Fuel pressure was one of the things I was more leaning towards, as it has all the symptoms of not getting enough juice. Ill check fuel pressure tomorrow once I can find my pressure tester. I hope it isn't the pump as its literally brand new.

IAC was aftermarket, but I can pull one from another Liberty I have to test.
 

Ksat

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To answer your question, yes, bad O2 sensors could cause your problem. After your first 2-3 minutes, the PCM could be switching from open to closed loop, where it starts relying on info from the sensors to make mixture adjustments. If one (of both) of your sensors is faulty and misreporting it's easy to guess what happens.

Pull the electrical connectors to both sensors, it should force the PCM to stay in open loop. Drive the vehicle and see what happens after your 3 minute window.

If you end up replacing them, NTK brand sensors are the only ones you should be buying.
 

tester

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Tried swapping out the IAC with another one from another Lib, no change (I did clean out the IAC port when I did swap it out the first time).
Unplugged the O2's, and it did the usual just faster.
Couldn't find my fuel pressure tester, so ill pick up one soon.
 

Ksat

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If the problem is pump-related, it might help to check that you don't have power or grounding issue. When testing pressure, make sure to check what it is when the engine is under load, as well.

Even though you said you don't have codes, if you have a live data-reading scanner, it would be prudent to look through the (mode 1) list and see what some of the sensors are reporting.
 

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