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Discussion Starter #1 (Edited)
Hello everyone,

Over the past 5 years, my 2003 XTerra XE 4x4 (160K miles) has seen a steady decline in MPG (250 miles/tank) and acceleration quality. The vehicle struggles to accelerate, especially on hills, and I often find it’s the slowest car on the road when accelerating. It idles around 1000RPM, and accelerates between 3-4000RPM. When I release the gas pedal on a hill or at highway speeds, the vehicle slows down abruptly and rapidly, meaning that I have to keep between 2-3000RPM just to maintain my speed. I’ve already had the following work done over the past 2 years (in this order), with minimal effect:
  • All 4 brake rotors and pads replaced
  • wheel alignment
  • Engine gaskets replaced - engine resealed. Compression tested.
  • ignition and starter fuses replaced
  • ignition wires replaced
  • ignition distributor replaced
  • various sensors replaced (not sure which ones)
  • Catalytic converters x2 replaced. This was due to a code being thrown, and only after the O2 sensors were replaced. Apparently, the CCs were in rough shape when they inspected them - and there were chunks of carbon (or ceramic?) on the inside. I remember one of the mechanics in the shop mentioned this could be indicative of a more deep-rooted engine problem, but the senior mechanic dismissed it claiming that the engine had already been examined thoroughly. I've seen mentioned on this forum that CCs should last forever - is this true?
My mechanic thinks it runs fine, but it just doesn’t feel right.

Any thoughts?? Thanks in advance
 

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Is the Service Engine light on?
Either way I would hook it up to a OBDII to have the codes read. Not all problems will trip the light.
 

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You could try cleaning the injectors, cleaning the MAF, making sure the air filter is clean and that there are no obstructions in the intake system before the filter (rodents like to make nests in the baffles and pipes). Also check your Fuel Pressure Regulator by disconnecting the FPR's vacuum line from the back of the intake manifold with the engine running. If fuel comes out of the line you know that your FPR has a perforated diaphragm and is leaking unmetered fuel directly into the intake (though this usually causes misfires and a code).

You could also pull your spark plugs to see if they have any build up. You can tell a lot by the color of the plugs and the amount of build up on them. If you haven't already, you should change your fuel filter. It's a $14 part that is often overlooked since most newer vehicles don't have a changeable filter. You're fuel filter is on the cross member forward of the fuel tank. Changing it consists of undoing two hose clamps, removing the hoses from the filter and installing the new one. Make sure you use a catch pan as you will lose some fuel. I recommend clamping the hoses before disconnecting them (just tight enough to squeeze them shut, but not tight enough to crush them).

I assume you mean that it slows down when you release the gas going down a hill and not up. Do you have it in overdrive (It should be).
 

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How well does the transmission shift? Delayed, late shifts or early? does it upshift or downshift too easily? The TPS is a big contributor to shifting and runability. Does the transmission complete all of its shifts?
 

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Discussion Starter #6
How well does the transmission shift? Delayed, late shifts or early? does it upshift or downshift too easily? The TPS is a big contributor to shifting and runability. Does the transmission complete all of its shifts?
There may be a delay getting into the top gear. Seems to downshift easily. I think the transmission completes all its shifts, although I’d have to count to be sure.
 

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When you decelerate, ease the trans into neutral see if it still feels abrupt when slowing down or if it seems to coast normally.
 

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Hello everyone,

Over the past 5 years, my 2003 XTerra XE 4x4 (160K miles) has seen a steady decline in MPG (250 miles/tank) and acceleration quality. The vehicle struggles to accelerate, especially on hills, and I often find it’s the slowest car on the road when accelerating. It idles around 1000RPM, and accelerates between 3-4000RPM. When I release the gas pedal on a hill or at highway speeds, the vehicle slows down abruptly and rapidly, meaning that I have to keep between 2-3000RPM just to maintain my speed. I’ve already had the following work done over the past 2 years (in this order), with minimal effect:
  • All 4 brake rotors and pads replaced
  • wheel alignment
  • Engine gaskets replaced - engine resealed. Compression tested.
  • ignition and starter fuses replaced
  • ignition wires replaced
  • ignition distributor replaced
  • various sensors replaced (not sure which ones)
  • Catalytic converters x2 replaced. This was due to a code being thrown, and only after the O2 sensors were replaced. Apparently, the CCs were in rough shape when they inspected them - and there were chunks of carbon (or ceramic?) on the inside. I remember one of the mechanics in the shop mentioned this could be indicative of a more deep-rooted engine problem, but the senior mechanic dismissed it claiming that the engine had already been examined thoroughly. I've seen mentioned on this forum that CCs should last forever - is this true?
My mechanic thinks it runs fine, but it just doesn’t feel right.

Any thoughts?? Thanks in advance
I had the same problems with my daughters xterra, same year and mileage as yours except hers is 2x drive. Knock Sensor was bad so it was replaced. still sluggish on hills, poor gas mileage, and struggled to pass cars on highway. replaced spark plugs and ignition wires and that solved the problem. Plugs looked fine but they were original so I went with what manual says and got new ones. Her fuel pump went out two years ago so it was replaced along with filter and we never realized poor performance at that time but she started complaining a couple months ago.
 
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