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Discussion Starter · #1 ·
What's up guys,

My problem with my 2002 Mustang is that every time after like 30-60 minutes of non stop driving, it starts to buck and jerk. The best way to describe it is if it's being choked. When starting from a cold start, it'll run fine with no trouble. Only when it has been driving for a while, this happens.

It gets to a point when I press on the gas pedal, it won't accelerate and the rpms would stay at 2000rpm. And at stops, the rpm's would bounce from 900 to 300 until dead. But if I parked and shut off the engine for a minute or so and start back up, it will drive fine again until it will jerk once more.

In short drives it'll never show, but for long drives it does. So far I have read a few forums to get something close to my experience. Hearing it could be from the mass air flow sensor and idle air control valve, to my coils and fuel filter. But i do believe its an eletrical issue. If its mechanical, this problem would stay rather than go away for a while just by turning it off briefly. So far what I have done was clean my mass air flow (It didn't show much filth but clean it anyway.) clean the throttle body and clean the idle air control valve. And the problem still persists. Recently check my codes, came back with P0135 (O2 Sensor Heater Circuit Malfunction Bank 1 Sensor 1) and pending P0174 (Fuel Injection System Too Lean Bank 2)

I replaced the O2 sensor upstream on the passenger side but no change. And along with checking codes everything was cleared but misfire.

If it is the other issues like the spark plugs, the coils or the fuel filter I'll give it a look over. Or would it be my throttle positioning system acting up? Or the PCV?

The mustang haves 175k miles on her; bought it that way. And only mod it has is a cold air intake.

Any help on this issue will be greatly appreciated. I do wish to just really enjoy the mustang on long Sunday drives without this killing my enjoyment.
 

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First, double check that there are no vacuum leaks, and make sure that all of the connections on the CAI are securely fastened.
Next, replace the fuel filter.If the problem still persists, do a fuel pressure test after driving the car for an hour to replicate the conditions that are causing the stumbling.
The fuel pressure at idle should be 35-55 psi. It should hold the operating pressure for five minutes, and lose less than 5 psi after the engine is turned off.
 

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Discussion Starter · #3 ·
First, double check that there are no vacuum leaks, and make sure that all of the connections on the CAI are securely fastened.
Next, replace the fuel filter.If the problem still persists, do a fuel pressure test after driving the car for an hour to replicate the conditions that are causing the stumbling.
The fuel pressure at idle should be 35-55 psi. It should hold the operating pressure for five minutes, and lose less than 5 psi after the engine is turned off.
Welp. I'll be damned. It was the fuel filter. If the owner didn't replaced the filter for so long that when I tilt the old filter, it spills black dirty gas, I definitely need to overhaul everything else. Thanks a bunch!
 

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Discussion Starter · #4 · (Edited)
First, double check that there are no vacuum leaks, and make sure that all of the connections on the CAI are securely fastened.
Next, replace the fuel filter.If the problem still persists, do a fuel pressure test after driving the car for an hour to replicate the conditions that are causing the stumbling.
The fuel pressure at idle should be 35-55 psi. It should hold the operating pressure for five minutes, and lose less than 5 psi after the engine is turned off.
Well after fuel filter replacement, 3 weeks later the problem came back. I bought a fuel pressure reader and at idle it holds 38psi. And it slowly loose 10psi after half an hour when its off.

Would it be possible that the fuel pump is next to change?
 

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Still the same symptoms? Hesitation after the car has been driven for a while?
Did you do the fuel pressure test after the car developed the hesitation?

The fuel pressure is kind of low. My theory is that the pump could be weak, and after it runs for a while, is not developing enough fuel pressure to properly run the engine. That is just one possibility, though.
Before changing the pump, you should check to make sure that there are no vacuum leaks. With the engine running, you can carefully spray some carburetor cleaner around all of the vacuum lines, the intake manifold, and anywhere that could potentially be a source of a vacuum leak. If there is a leak, you will notice a change in the engine idle when spraying the area where vacuum is leaking.
 

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Discussion Starter · #6 ·
Still the same symptoms? Hesitation after the car has been driven for a while?
Did you do the fuel pressure test after the car developed the hesitation?

The fuel pressure is kind of low. My theory is that the pump could be weak, and after it runs for a while, is not developing enough fuel pressure to properly run the engine. That is just one possibility, though.
Before changing the pump, you should check to make sure that there are no vacuum leaks. With the engine running, you can carefully spray some carburetor cleaner around all of the vacuum lines, the intake manifold, and anywhere that could potentially be a source of a vacuum leak. If there is a leak, you will notice a change in the engine idle when spraying the area where vacuum is leaking.
Aye I forgot to mentioned that i did do a vacuum check and there is no leaks. I did think that maybe the socks that are on the pump is dirty along with the pump slowly dying. I also been told to run a full tank of premium twice to see if it helps. Ill report any updates along the way.
 
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