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FixItMan
FixItMan, Master Technician
Category: Jeep
Satisfied Customers: 17340
Experience:  AA DEGREE AUTOMOTIVE/DIESEL TECH
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My exwife has a 2004 Jeep Liberty sport with a 3.7 Liter

Customer Question

My exwife has a 2004 Jeep Liberty sport with a 3.7 Liter engine (it's also 4x4). Occasionally when it's started, it acts as if it wants to die. She bumps the Gass peddle a couple times and after 30 seconds or so it starts to run fine again with no more
problems until it has been shutoff for 20 minutes or so and is restarted. Having worked on cars most of my 52 years, I've ran computer diagnostics on it. The computer reports that a couple of the oxygen sensors are bad even though 3 of them have been replaced.
Any idea?!? Or any questions I can answer to help lead you in the right direction?
Submitted: 1 year ago.
Category: Jeep
Expert:  FixItMan replied 1 year ago.

Hello, my name is Bobby. Thank you for the question. Most of the time this is caused by an overly dirty throttle body. I would check and see if it is dirty. If it is then clean it and see how it runs. If it continues then you may need to check the signal from the TPS to see if it is reading correctly. Have these been checked?

Customer: replied 1 year ago.
I've looked at the throttle body somewhat but didn't really suspect it. What arrears need inspected and if they are dirty, what do you recommend for cleaning.
Customer: replied 1 year ago.
Sorry, auto correct. What areas should be inspected.
Expert:  FixItMan replied 1 year ago.

The main thing is the throttle plate and bore. If there is even a little build up between then this will occur. The absolute best way to clean it is to remove it and thoroughly clean it with throttle body cleaner and wipe it out with a lint free cloth. If you do not want to remove it you can clean it as good as possible with it still installed on the engine. Just make sure that the key is off and that you open and close the throttle plate slowly as fast motions can damage it.

Customer: replied 1 year ago.
What about the TPS. I have a diagnostic computer that I can hookup to the Jeep and watch the signal real time (if that sensor is available for monitoring). What should I expect to see on the monitor and if I can monitor it, is there a test to perform to check it?
Expert:  FixItMan replied 1 year ago.

Really the main thing you want to see is a nice and even increase and decrease in voltage or angle, however your scan tool reads it.

Customer: replied 1 year ago.
What about the analog check in case it can't be viewed?
Expert:  FixItMan replied 1 year ago.

Either way you want a nice and smooth increase and decrease in the signal.

Customer: replied 1 year ago.
Ok, it's 1:30 AM here. I'll check those first thing tomorrow and see what happens. I'll get back with you afterwards. Thanks much for your response!
Expert:  FixItMan replied 1 year ago.

No problem. I will look for your response. Have a good night.

Customer: replied 1 year ago.
Ok bobby, here's where I'm at. I spent the day working on the Jeep. I took the Throttle body apart and cleaned it, replaced the Throttle position sensor, replaced the Idle Air Control Valve and yet it still does it. I do, however, have some additional info that may help or it may just add confusion into the mix. I checked the codes again and got 4 of them. The one that interests me most is the:
P0300 Random Multiple Cylinder Misfire detected.
the others were:
P0138 O2 Sensor circuit high voltage bank 1 sensor 2
P0158 O2 sensor circuit high voltage bank 2 sensor 2
P0032 HO2S heater control circuit high bank 1 sensor 1I'm assuming the last three are probably because of the misfires. I may, however, be able to give you a better description of what's happening. When I first start the Jeep, it runs fine. After about 2 or 3 minutes of idling it starts to run rough and gets worse, sometimes to the point of dying other times not. Once I give it some gas and get past the point of rough Idle, it seems to stop doing it until I shut it off for 15 to 20 minutes. After that time period I can start it up and it runs good for the 2 or 3 minutes like I said earlier then starts acting up again. Any thoughts?
Expert:  FixItMan replied 1 year ago.

Can you tell me if your scan tool reads live engine data? If it does then please tell me what the fuel trim readings are when the vehicle is acting up.

Customer: replied 1 year ago.
It does read live engine data. All of them are abbreviated. I'll record the data and post all results tomorrow.
Expert:  FixItMan replied 1 year ago.

No problem. What I am looking for is LTFT and STFT.

Customer: replied 1 year ago.
If I remember correctly it said overload fault but let me get recordings both running good and acting up and I'll post.
Expert:  FixItMan replied 1 year ago.

Sounds good. I will look for the post when you can get to it.

Customer: replied 1 year ago.
Ok bobby, here are 2 files for you to look at. They should be self explanatory. Let me know if you see anything of if there's anything else I can send you.
Expert:  FixItMan replied 1 year ago.

I am away from my PC at the moment so I cannot open them. Once I get back to it I will check them out and let you know what I think.

Customer: replied 1 year ago.
That's fine. Thanks.
Expert:  FixItMan replied 1 year ago.

Be back in a bit.

Expert:  FixItMan replied 1 year ago.

From those readings it looks as if the engine is running rich when the problem is occurring. From what I can tell the MAP sensor seems like it is not reading correctly when the problem is occurring. I would remove it and make sure it has a good vacuum source. I would also tap on it with the handle of a screwdriver when the engine is running and see if the idle changes at all. If it does then replace it.

Customer: replied 1 year ago.
I'll have to double check (and you know more about it than I ) but the MAP sensor on this is electronic (or am I thinking Mass Air Flow Sensor?).
Customer: replied 1 year ago.
Nevermind, forget that last question. I'll check it this afternoon. Thanks.
Customer: replied 1 year ago.
As you can see from these pictures, there,s no way to check the vacuum (unless I measure complete system vacuum). Replacing to see of this resolves the issue, I'll let you know what happens.
Customer: replied 1 year ago.
Here is the second picture.
Expert:  FixItMan replied 1 year ago.

Did you tap on it while the engine was running?

Customer: replied 1 year ago.
or at least the best I could, It's in a tight spot). Since it sidn't make any difference I just went ahead and replace it. So far it hasn't done it but I'll give it a day or so to see if that really took care of it.
Expert:  FixItMan replied 1 year ago.

Let me know what happens and we can continue if needed.

Customer: replied 1 year ago.
That still did not take care of it, what's next.
Expert:  FixItMan replied 1 year ago.

Do you happen to have a vacuum gauge? If you do can you tell me what the vacuum is at idle and what it is at 2500 rpm and also how stable it is.

Customer: replied 1 year ago.
I do. I'm out of town for the weekend but I'll check when I get back.
Expert:  FixItMan replied 1 year ago.

Thank you. Have a great weekend.

Customer: replied 1 year ago.
Vacuum test reads 18 in Hg consistently. No variation.
Customer: replied 1 year ago.
NO variation at idle.
Expert:  FixItMan replied 1 year ago.

My last options are that the throttle body itself is failing or you have a programming problem. Will it typically always idle fine again if you rev it a few times?

Customer: replied 1 year ago.
No. Actually when you try and rev it up it doesn't want to accelerate. I did notice while checking the vacuum, it seemed to run better when I pulled the vacuum line off to run the test and when I tried to put the vacuum line back on it actually killed the engine.
Customer: replied 1 year ago.
Curious, a couple times now you have mentioned the throttle body. What I call a throttle body was a cross between a carburetor and full injection spaying fuel into the engine. This is fuel injected and the only thing the "throttle body" does is supply air.
Expert:  FixItMan replied 1 year ago.

Yes, the throttle body controls the amount of air entering the engine. From what you are saying it sounds like the throttle plate itself may be hanging up. Does it have a throttle cable on it or is it all electric?

Customer: replied 1 year ago.
It has a cable. I've watched it when acting up (that's where we started with this) and it's not hanging up. The plate soesn't even have to move.for the problem to start. Start the vehicle and let it idle without touching the gas pedal and it starts acting up.
Expert:  FixItMan replied 1 year ago.

I went back through our discussion to see if we talked about the idle control valve. Have you checked this?

Customer: replied 1 year ago.
I've changed the throttle position sensor, Idle air control valve and MAP sensor along with disassembling and cleaning the throttle body.
Expert:  FixItMan replied 1 year ago.

Besides the possibility of a fuel pressure issue, which I think is unlikely, I think that the computer needs to be reflashed. I think that there is a programming issue.

Expert:  FixItMan replied 1 year ago.

Besides the possibility of a fuel pressure issue, which I think is unlikely, I think that the computer needs to be reflashed. I think that there is a programming issue.

Customer: replied 1 year ago.
I put a fuel pressure gauge on the fuel rail and the pressure was at 60. It did oscillate between 60 and 65 but that was it. I can't see a computer flash being the issue as that would be a constant thing and not intermittent. Any other ideas??