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Wonder if anyone could help before I lose the will to live with this issue.

I have a Peugeot 207 1.4 petrol 16v done about 125,000 miles, the car starts perfectly every time, but when the engine is cold I have to sit there for at least 5 mins until the engine warms up, then I can drive off.

If I don’t let the engine warm up, I drive off and the engine is sluggish, pedal to floor and no movement, then it will all of a sudden kick in, if I stop at junction the engine will cut out.

When at Idle also sounds rough until it has warmed up.

I have changed the following:

  • Spark plugs
  • Coil pack
  • MAP sensor
  • Camshaft sensor
  • Variable valve oil solenoid sensor

I have also checked for a compression leak by spraying cold start spray around the vacuum hoses, intake manifold and throttle body area and can’t see any rev changes.

I have no engine management light on and no error codes when scanned.

I have attached a live data scan of a short journey which shows erratic LTFT is this normal?

Anyone else come across this problem before?

enter image description here

One item I forgot to list above was that I have previously checked the coolant temperature sensor and it read correctly, I don’t appear to have an oil temperature sensor on my scanner for this vehicle. I have added a further snap shop with the oxygen sensors also attached.

Thanks for you replies so far

enter image description here

Additional Info

I’ve run this scan, not sure if it helps

enter image description here

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  • O2S2 should be your post cat sensor. I'd expect this to read fairly steady as long as the O2 and cat are working correctly. Also, I thought O2 sensors only had a range of .1 to .9 volts, so I'm not getting why S2 is reading higher and lower than that? Especially when it should be sitting around .5 volts to begin with. With responses like that, I'm surprised you don't have a P0420 code popping for a bad cat. Dec 1, 2022 at 20:58
  • So do you think it could be a bad cat? Dec 1, 2022 at 22:59
  • I really don't know what to think. I'm just saying what I'm seeing is all over the place. Really crazy. Dec 1, 2022 at 23:19
  • It’s been driving me mad for about 2 years! lol is there another scan I can do with other sensors that would help? Dec 2, 2022 at 5:25
  • There seems to be a loose correlation between the weird rpms and the o2s2, which makes me wonder if you have a sticky injector which periodically works when cold and when warmed, works better, so its dumping fuel through the cats
    – Chris
    Dec 2, 2022 at 18:10

1 Answer 1

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I'm not a fan of using fuel trim values to diagnose engine problems, there's a lot of rabbit holes there. The fluctuation of the long term trims is certainly an indicator something isn't right, it's just working out what is wrong from trims has never worked for me, although others may have a better answer. The shifts in the data could be an artifact of the OBD reader, the software you use to interpret it, or the sign of a different issue. Instead I suggest working on the symptoms that are more straightforward, and I don't think you have exhausted the possibilities yet.

In addition to what you have checked already rough running when cold is a classic symptom of a faulty coolant temperature sensor. If your engine's computer has the wrong coolant temperature data then it will give the wrong fuel-air mix and you will have rough running when cold, perhaps poor performance all around and bad fuel economy.

You can check this with your OBD reader, look at the coolant temperature and oil temperature readings when the engine is cold, they should match or be close to the outside air temperature. If one or the other isn't accurate check the connection and replace the sensor as needed.

It also is worth checking your idle control valve and EGR valve as those can cause rough running and idling, although that would usually be consistent whether cold or hot.

Once you have the rough idle fixed have a look at the trims again, if they are back to normal then all good, if they are still fluctuating you may have something else going on.

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    I can see the STFT being erratic, but the LTFTs? They should be fairly steady with small changes, right? Not sure what that would point to, but its saying something to me. If I'm reading the graph right, the LTFT are hitting 100% routinely ... that's crazy. As you state checking the temp sensors is a good move, no doubt. Dec 1, 2022 at 14:32
  • I'm not saying the long-term trims being erratic isn't the sign of a problem, I'm saying trying to work the problem out from the trims IMO isn't the way to diagnose anything @Pᴀᴜʟsᴛᴇʀ2. I've edited for clarity.
    – GdD
    Dec 1, 2022 at 14:37
  • Oh, wasn't complaining about anything you've stated ... just pointing it out. Some weird stuff going on is all I was getting at. I agree with your assessment. Dec 1, 2022 at 15:11

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