Flat spot on acceleration

[expatexplorer]

I have a 2005 V6 4.0L Ford Explorer.

I am experiencing a rough idle issue that is proving hard to debug. Apart from a rough and stumbling idle, you can also detect that the car seems to miss slightly when cruising and hold a steady speed at 100-110kph.

When you accelerate from idle, it seems to have this flat spot at 1000rpm where it feels like the motor has been switched off, then picks up at again at around 1200rpm. It is like somebody has turned the key off.

The other interesting symptom is that I can slowly build up to revs from idle to about 1000rpm, then it drops to 900rpm and creeps back to 1000rpm. It oscillates between 900-1000rpm all day if you hold it there.

I have had the car back to the dealer many times. They tell me that it throws no codes and the scanner reports that all sensors are ok. They have given it a tune up and replaced many things including the harmonic balancer.

When I pick the car up, it runs fine for a short time then reverts back to its old ways, I guess this is the PCM module relearning problem.

To me it sounds like it might be a fault with the TPS or the throttle body, perhaps it has a flat spot on the TPS sensor that is not picked up in any error code. It feels like an electrical issue as it runs perfectly otherwise and the fuel consumption is pretty good. Has anybody come across this problem before? I think the dealership have run out of ideas, if I need to throw parts at it, I want to be throwing the correct parts.

 

[Chris Harrach]

I have a 2005 V6 4.0L Ford Explorer.

I am experiencing a rough idle issue that is proving hard to debug. Apart from a rough and stumbling idle, you can also detect that the car seems to miss slightly when cruising and hold a steady speed at 100-110kph.

When you accelerate from idle, it seems to have this flat spot at 1000rpm where it feels like the motor has been switched off, then picks up at again at around 1200rpm. It is like somebody has turned the key off.

The other interesting symptom is that I can slowly build up to revs from idle to about 1000rpm, then it drops to 900rpm and creeps back to 1000rpm. It oscillates between 900-1000rpm all day if you hold it there.

I have had the car back to the dealer many times. They tell me that it throws no codes and the scanner reports that all sensors are ok. They have given it a tune up and replaced many things including the harmonic balancer.

When I pick the car up, it runs fine for a short time then reverts back to its old ways, I guess this is the PCM module relearning problem.

To me it sounds like it might be a fault with the TPS or the throttle body, perhaps it has a flat spot on the TPS sensor that is not picked up in any error code. It feels like an electrical issue as it runs perfectly otherwise and the fuel consumption is pretty good. Has anybody come across this problem before? I think the dealership have run out of ideas, if I need to throw parts at it, I want to be throwing the correct parts.

I had a problem with a rough idle and the same ossilating issue in my '97 E.B. Explorer. It turned out to be the Idle Air Control valve. I changed it and that was the end of it. Im not sure if the same valve or one similar, is on a 2005 Explorer, but replacing it would be a good place to start. It sit's on top of the engine close to the firewall (at least it does on my '97) and is held in place by 2 bolts and an electrical connecting plug. I got mine at Auto Zone & it was $111.00, (A bit pricey) but came with a lifetime guarentee. Hope this helps.

Good luck.
Chris H.

 

[expatexplorer]

I had a problem with a rough idle and the same ossilating issue in my '97 E.B. Explorer. It turned out to be the Idle Air Control valve. I changed it and that was the end of it. Im not sure if the same valve or one similar, is on a 2005 Explorer, but replacing it would be a good place to start. It sit's on top of the engine close to the firewall (at least it does on my '97) and is held in place by 2 bolts and an electrical connecting plug. I got mine at Auto Zone & it was $111.00, (A bit pricey) but came with a lifetime guarentee. Hope this helps.

Good luck.
Chris H.

Thanks for the tip, it turns out that the 2005 model is 'drive-by-wire' and does not have the IAC valve.

After a lot of research and reading on this site I decided to take a bet and replace the fuel filter. Whilst it was clogged and dirty, it did not solved the problem.

I then took another gamble and replaced the fuel pressure sensor. BINGO ! - fixed the problem. The truck drives like new!

I am guessing that the FPS must have been on the way out and was sending bad info to the computer which was compensating by varying the pressure or flow rate making the revs fluctuate. It was not throwing codes so I was flying blind as to the source of the problem. I guess this is why having a scanner is a must better diagnostic tool than just a reader as this would have shown a problem with the pressure fluctuation.