Throttle increases when idle & fluctuates when driving.

[jtaling]

Hi,

I have been trying to sort out this problem for months and have ran out of ideas so any help will much appreciated!

The problem-
When the car is started it will run at around 1,100rpm then slowly increase to about 2,300rpm and stay idle around there.
Once you start driving you wont notice much effect when its in gear (occasionally it can slightly accelerate by itself when in gear) but the moment you push the clutch in the throttle will jump to about 3,000rpm and go back to 900rpm and jump back up to 3000rpm all in the space in a second or two! It will keep doing this until you put it in gear again and start driving!

The solutions I have tried already-
-We have cleaned the throttle house body a couple of times but this seemed to have only made the problem worse.
-The accelerator pedal has also been replaced but has been no help
-Called the AA to have a look at it and they found nothing
-Took it to a Renault dealer for a system reset and hasnt helped. Also the CLIP is able to find any error codes.
The dealer said it probably could be a lose wire somewhere??

About the car-
Car-Renault Megane II 1.4 Dynamique 3-door
Location-Buckinghamshire UK
REG-05
Date purchased- 1/3/2014
Mileage-46,000



Many thanks for your help and will be happy to provide any more details if I've missed out any!

[fredcamp2]

The problem your encountering with your megane is much more than likely a wiring problem interference from another circuit a very common problem on these is the wiring at the metal cage on ecu gets chaffed & certainly causes the over revving. This has to be checked out starting at the 6 terminal pedal sensor clearly marked 1to 6 the wires from pedal sensor has to be checked at the ecu corresponding pin no's Can you post up your engine code starting with k4j ??? Hth fredcamp2

[jtaling]

Thanks for the reply and the help!

The engine code is k4j 732! Am not too sure what you mean by the corresponding pin numbers?

Again thanks for the help!

[AlexB]

Is it a kind of vroom-vroom at the red light syndrome? I had this in a TTS when a valve in the crankcase ventilation circuit failed. Audis and VW are notorious with this.

The other things to look at are a possible air leak into the intake and O2 sensor faults. Use OBD live data to analyse the problem, look at the fuel trim values first. Don't rely on the dealers or anyone else who use OBD only for the trouble codes.

[fredcamp2]

The acc pedal sensor has a 6 terminal plug clearly marked 1-2-3-4-4-5-6
No 1 signal return wire to ecu pin no bf3 wire colour beige
no 2 5v feed from ecu pin no bf2 wire colour brown
no 3 5v feed from ecu pin no bg2 wire colour green
no 4 signal return wire to ecu pin no bh2 wire col0ur violet
no 5 earth wire at ecu pin no bh3 wire colour violet
no 6 earth wire at ecu pin no bf4 wire colour orange
As you can see from these there are 2 5v feeds 2 earths & 2 signal return wires to the ecu. The throttle valve control unit also has a 6 terminal marked 1 to 6
no1earth at ecu pin no bg4
no 2 ecu pin no bg3 signal return wire
no 3 12v feed from ecu pin no bm4
no 4 earth at ecu pin no bm4
no 5 5v feed from bg2
no 6 signal return to ecu pin no bd3
I would recommend this wiring be checked out by a competent person. Acc pedal sensor at key on throttle valve fully open 3.5-4v at ecu pin no bh2 Acc pedal sensor at ecu pin no bf3 key on throttle valve fully open voltage should read approx. 1.75- 2v's
Hth Regards fredcamp2

[TAS]

Before getting too involved.
Can you plug clip in and look at the alternator load % in the UPC. Is it up around the 99% mark all the time?

[jtaling]

Thanks for all the replies!

Fredcamp2- all the wires seem to be working okay! they all seem to be conducting anyway! just a little error i spotted was the no 4 throttle valve should have gone to m3? it seemed to work there. Thanks for the help though and any suggestions what to do next maybe?

TAS & ALEXB- I dont have a clip but am using the torque app with an obd reader (elm327). What sort of fuel trim values should i be looking for? And also am I able to look at the altenator load % with an obd reader? Thanks for your help too!

[fredcamp2]

Can you elaborate more how you checked the wiriing hopefully not by doing a continuity check car wiring has to be checked out by carrying out a load test I'm quite aware the alternator on these has to be configured to the (upc) engine bay fuse fusebox I can not see this problem tied into the alternator. Can you explain how exactly this wiring was checked out Regards Fredcamp2

[TAS]

I think you can only read the alternator load % using clip or autologic.
Most idle problems on these end up being a faulty throttle body.
I have had a couple cars that have come to me from other garages with idle problems after they have checked all the usual things and I always check the load and make sure the correct alternator type is input first as it only takes literally 5 mins. If the load output is excessive the injection computer increases the idle to counter for this and does not throw up any fault codes.
This isn't a really 'common' issue but it does happen so please don't dismiss it and obviously it's not a 5 min task for yourself because you don't have clip. If you manage to find someone with clip check it and have the values reset.

[fredcamp2]

Tas please take note to check out alternator is best done using a oscilloscope which shows the presence of a square pulse signal calibration 2.5v/div time base 2ms/div. 70% of faults on these are certainly down to wiring problems or faulty earths could be interference from other circuits It would do no harm to check out the status of both clutch & brake

[jtaling]

Hi fredcamp & TAS!
Apologies for the late response. Had to go back to university for a little bit. But back now and it turned out it was the alternator! So many thanks for your help! Saved a lot of money!

Unfortunately while replacing the alternator my dad short circuited the car and we think we need a new ECU. The car runs absolutely perfect now but suddenly and randomly will jump up to 3,000-3,500 rpm and stay there. Pressing the throttle wont make any difference and the only way to stop this is by turning the engine and also removing the key! We have been looking for 2nd hand ECU's and were wondering which numbers need to match. We have found nearly identical ones (in the photo the red boxes with have matched) but have only been able to find ones ending in 2A whereas ours ends in 2B. Does this matter?

We have also been looking at maybe getting a 'unlocked' ECU from https://www.cartechelectronics.com/ to save replacing the key and etc. Is this a good thing to do?

I will post this as a new thread aswell. Many thanks for you help again!