Peugeot 307 idles high after about 18 minutes from a cold start

Check / replace engine coolant temp sensor . Should be fault codes if " lambda reading high failing emissions. " which will probably be the cause of fast idle . Check MAF sensor . On a car of that year there can be many causes of engine tapping noise especially if servicing not been properly maintained

Hi Whittingehame,

Thank you so much for your response and willing to help! I have suspected the engine coolant temp sensor, is that the same thing as a thermostat?

No fault codes on both the old and new o2/lambda sensor. Both activate shortly after a cold working within the volt range of .1 to .8.

Is the MAF sensor the same as the EVAP sensor or the petrol purge valve? I spoke to my mechanic today and he said the tapping noise is from the purge valve and to check for any hissing sound coming from opening the petrol cap which would indicate air/vacuum in the petrol tank which could lead to high air to petrol mixture causing the weird high idle after warming up.

I also wondered, failing that to check for leaks using a smoke test and maybe even have a mapper edit the ECU's fuel-to-air ratios and make the mixture a bit more richer or more balanced.

The temp sensor is different from the thermostat and sends info to the ECU on requirements of fuel and other matters and regulates needs . MAF sensor is different from the EVAP sensor .

Hi again Whittingehame,

Thank you for clarifying the the temperature sensor is not the same as the thermostat and that the Mas Air flow Sensor {MAF} is not the same as the as the Evaporative Emissions Control system {EVAP}

I am using Torque pro to read for any error codes {none at all for now} and also read the live data when engine is running.

What's weird is there is no reading for MAF sensor but there is one called 'inlet manifold pressure' reading which I am not sure could be a reading from the MAF sensor?

Also there is no 'temperature sensor reading' but there is a temperature reading for 'thermostat' and 'intake air temperature', I am guessing the 'thermostat' reading is the 'thermostat' reading and not the 'temperature sensor' reading?

And the 'intake air temperature' is the temperature reading of the surrounding environment by the temperature sensor?

Although there are no error codes doesn't mean that something might not be wrong with the sensors you've mentioned, I have also learned the best diagnostic software and tool for Peugeot and Citron cars is using the dealership software called Peugeot Planet 2k {PP2K} and its accessories according to numerous sources on Peugeot forums.
Google search: "PP2000" "Lexia" "Peugeot" to see the kit

I asked the same question on Reddit's Peugeot group and the response was the suspect to be the MAF sensor and to have a scan through the recommended PP2K software by contacting an owner through the database of owners of the kit who provide diagnostic at low cost than dealerships.

I have joined the group and I am awaiting approval:

Or I might have to invest in the Kit hoping will work on Windows 10

In regards to the tapping noise and my mechanic pointing the noise is actually coming from the petrol purge valve and could be the cause of the high idle issue due to too much air going into the ignition area in which case the petrol purge valve might need changing, the recommendation to check was to open the petrol cap and check for hissing or air escaping sound.

I did that today and was surprised as not only was there air hissing out but I could hear the petrol tank giving of creaking sound as if tension was being released. Tried again in a few hours and the same result. I hoped the high idle issue was all due to trapped air and ran the engine to warming level but the high idle at thermostat reaching 80 degrees is still there lol

So I am now suspecting the MAF sensor, temperature sensor, and petrol purge valve

Changed the engine temperature sensor, but still a high rev problem at the thermostat temperature reaching 60 and a:

'P0711 Transmission fluid temperature sensor A circuit range/performance'

fault code on a plug-in V309 diagnostic tool but no errors on Torque pro via Bluetooth.

The next suspect is the MAP than the throttle body. I also suspect a possible leak so a smoke leak test as well.

Check the engine crankcase breather / pipes . If leaking they will be drawing air and engine running lean which can cause high idle

We've tried brake cleaner spray around possible leak areas but non detected, next up is a :

1. smoke test to detect leaks

2. Manifold Absolute Pressure (MAP) sensor

3. Then the whole idle air control valve which is electronics based and integrated with the whole throttle body (has been cleaned thoroughly and checked through Torque pro for any sticking or stopping when pressing or releasing the gas pedal)

I believe the high rev issue is due to a high air-to-fuel mixture leading to a high lambda reading (lean) resulting in an MOT emission failure.

If all else fails my next suspicion is a possible engine knocking issue despite new spark plugs and ignition coils to resolve a cylinder 4 misfire.

The engine was also rebuilt late last summer due to a snapped cambelt so has been thoroughly decarbonized/cleaned, replaced engine head, pistons, cambelt, head gasket, and pumps.

Timing is perfect so are fuel pressure, and engine cylinder pressure.

Ran a smoke test, sealed every leak pre air filter and post air filter all the way to throttle body, new crank case breather hose/pipe. Ran a full scan using peugeot planet 2000 via diag box and the lexia cable kit as recommended by the peugeot community. There were 4 faults that initially showed up, 1 permanent the other 3 intermittent, which no longer do show up. Didn't make a note. All were p(powertrain) fault codes i think. So been looking at the live data, the manifold pressure drops down to 340 mbars when the high idle kicks in, 340 is way below the recommended mbars which is 400 to 420 mbars on idle. I also noticed the battery is at 14.2 volt, .2 more than than the recomended by peugeot planet 2000 which 14v so i turned a lot of power consuming features like heating, ac, hazard lights, beam light on...as the battery drops in volts due to power consumption so did the high rev from 1200rpm to 800...ive got a new throttle body and map sensor to fit but doubt that will fix the issue and that the issue is either a high volt issue or still an undetected leak somewhere or a mixture of one or two of the above mentioned issues

LOAD test your battery after lying overnight , prior to starting . Check your alternator for overcharging . If over charging may have fried your battery and even damaged electrical circuits

Replaced the map sensor, slightly better but not entirely, then fitted the new throttle body which seems to have done the trick!

Been monitoring via the app 'Torque pro', the new throttle body refuses to open up more than 8 to 9 % even when engine seems to be requiring more air{either because of a vacuum leak or normal standard I'm not sure)...

The previous/old throttle body used to open up to 11 and even 13 % leading to a kick in of high revving when engine warm....took a while for the new throttle body to calibrate.

I used the app 'throttle reset' {of which has a generic/universal reset for any brand vehicle and a BMW specific option too} , started to high rev ones so pushed the gas pedal for a few revs then the rev came right back down to normal range +/-700rpm.

I followed followed by engine off for 10 seconds and restart....engine rev on idle seems to be much better now at give or take -/+700rm and does not go into high rev even at thermostat reaching and over 90 hot...

Seems like either the electrical throttle idle air control valve {IACV}, throttle position sensor, or throttle motor, in the throttle body had somehow gone/worn past the recommended range,...

I think now the car will pass the emission test as the air to fuel seems back to normal. I'm going to monitor the situation further and post an update

All good and passed! There was a small leak top side of exhaust pipe leading down from cat which was letting air out, with that sealed, the revving issue sorted with the new throttle body installed, the Peugeot 307 has passed mot and the emissions test, thank you for your support whittingehame

Good you got it fixed and passed . Thank you for updating the forum

Thanks, the process of DIY was daunting to start with, but with your, Youtubers, local garage mechanics, Reddit, online articles, and Facebook (mechanic, Peugeot community pages) I've learned so much about the problem plus more on how cars work. I'm helping people with similar plus other problems and amped up to learn and do more too :-)

Good to hear , keep it up .