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2004 Mustang GT running lean, poor idle, loss of power

20541 Views 12 Replies 3 Participants Last post by  AdmiralSavage
Hello everyone. I'm new here so bare with me but I will be extremely grateful for any help I receive.

I got my 2004 GT about a month ago and it has roughly 190,000 miles on it. It started with code 0301 (misfire on cylinder 1) so I replaced the coil and plug, problem solved.

Shortly after it threw code p2195 (Bank 1 Sensor 1 Stuck/lean) and started idling pretty rough at stops. After reading a bunch of forms I was pretty convinced the rough idle was a misfire so I replaced all the coils and plugs and had no results. A family friend replaced both sensors on bank 1 and the code went away and the car was running normal, (no rough idle).

A few hours after I got rid of code 2195, code 401 pops up (egr insufficient flow) and the rough idle comes back. What I found was a brittle egr vacuum hose taped together so I replaced it with a soft line, deleted the code, and it hasn't come back. A significant amount of carbon did fall out when I removed the line from the egr diaphram.

I went awhile without any check engine lights but recently I started throwing code 2270 (bank 1 sensor 2 stuck lean). This is one of the sensors that has been replaced.

Right now the car's idle has awful shaking and surging that gets worse with the a/c on. For the most part I don't feel it when the car starts rolling. I do not know what type of o2 sensors were put on the car but the family friend who builds drag racing engines and is a mechanic very familiar with fords said they were "racing o2 sensors" and they would work fine. So I didn't second guess it but probably should have figured out what brand they were now knowing that if they are bosch sensors my car wont like them.

If these were bosch o2 sensors would it cause my car to run this poorly?

Here's a list of what I've tried.

- new coils and plugs
- cleaned maf sensor
- replaced fuel filter
- checked for vac leaks with carb cleaner (I couldn't find anything)
- ran injector cleaner
- replaced the o2 sensors on bank 1

The car definitely had heavy modifications on it before but it looks like the previous owner put everything back to stock accept for the cold air intake and it is h piped. There is an extra pulley with nothing on it that looks like went to some kind of forced induction.

I'm stumped.

I don't want to bore everyone with too much writing so if you are missing any information that would be useful let me know!
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You are making one of the most common mistakes most ppl make working on a PCM controlled car. That is assuming that an O2 sensor DTC means a bad O2 sensor. In the vast majority of cases, an lean O2 DTC means a vacuum or exhaust leak.

Don't over look the PCV system. When was the last time the PCV valve was replaced?

For the EGR related DTC, clean the EGR passageways in the throttle body.

Note, if there is still a leak to/from the DPFE lines, this could also be the source of the the exhaust leak.

Does this car have a non-stock cam?
I'm not sure if it has a stock cam or not. What would be the easiest part of figuring that out? I've looked pretty hard for a vac leak but have had no luck, I might just pay a shop to look for one. Wouldn't an exhaust leak be more likely to make it run rich?
An exhaust leak will make the motor run RICH. However the PCM will think that the motor is running LEAN.
My spark plugs are chalky white though? wouldn't they be black if it was actually running rich.
If the motor is actually running RICH, then the plugs would be black.

Does your motor use/burn coolant?

If the plugs say lean, then the odds still favor an intake leak. Don't cut corners here. Check anywhere air can enter. Valve cover gaskets, Injector O-rings, PCV valve (don't ignore this as it's on the same side).
The elbow of the pcv line that goes into the valve cover kinks when the engine is turned on, could that be causing this big of a problem? I can hear a small hiss when the car is running that will completely go away and come off intermittently. I've tried spraying carb cleaner and I even tried the cigar smoke trick trying to find a leak but no dice.
Oh and I don't think it's burning or using coolant. I checked it's level today and it was full. It did look like it had a little bit of debree in it though.
Thank you wmburns for all the input you have given me so far.
I replaced that pcv elbow with one from autozone but it sucked flat even quicker than the other one so I swapped it back. Also I found a bolt missing from the intake manifold behind the throttle body. Could that be an issue at all?
Re-reading the P2270 DTC and the DTC calls out the REAR O2 sensors. This DTC could be caused by:
  • removing the cats
  • excessive oil consumption
  • coolant in the exhaust
  • modifications affecting the rear O2 sensors such as anti-foulers.
  • blocked or bad cats
  • wiring fault to the sensor
  • swapped O2 sensor pigtails

Have the cats been removed as part of the H-pipe install? If so, this is the source of the P2270 DTC.

To everyone reading this post. In latter model year Fords, the PCM programming is much smarter. The PCM runs a test that creates a rich condition to CONFIRM that the rear O2 sensors are working. That means that some O2 eliminators won't work on the 2004+ model years.
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I was out of town for the weekend, I'l check if the cats were removed in the morning. It had to pass texas inspection though so I'm guessing it definitely has the cats.
Hey WMBURNS, I replaced the o2 sensors the other day. The replacements on bank 1 were bosch sensors, swapped them with new motorcraft sensors.

I did learn while replacing them that the rear cat's have been removed. Maybe I have a clogged cat? This morning I heard rattling from the rear end at a red light. After that I couldn't replicate that sound at any other light. When I put my hand over the exhaust, the passenger side blows a little hot while the driver side doesn't blow much heat at all. I'm not familiar with exhaust problems at all and appreciate your input!
Im having almost the same problems as you, i even put in a stock 4.6l engine since the other was heavily modified. I have replaced pretty much every sensor on the car. The car will not hold an idle and smells rich, my fuel trims looked really high. I was getting a code for bank 2 lean, p1151 and also p1401 for the dpfe sensor. I checked for vacuum leaks i could not find any after spraying carb cleaner all over the engine bay. Ive replaced o2 sensors also, the problem persists. The car will idle around 950rpm without ac. When i turn the ac on it will start to idle at 700 immediately. Sometimes the idle will surge up and down on its owm and stall out the car. Only thing i can think of is a failed pcm???
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