High idle after engine swap on Citroën C3 1.4 petrol 2005 (TU3JP/KFV)

[Nadzag]

Hi everyone,

My 2005 Citroën C3 (TU3JP/KFV engine) has a high idle, staying stable around 1,500 RPM, after an engine swap. I’ve already tried several things:

-Cleaning and swapping the throttle body
-Checking for vacuum leaks
-Swapping injectors
-Swapping the MAP sensor
-Checking CTS, MAP, O2 sensor values (ok)
-Measuring compression, which came out fine

No fault codes.

At this point I’m a bit lost and not sure where to look anymore. Maybe I should just drive the car like this for a while. I drove it shortly and it has power and feels normal, but the idle stays high when stationary.
It has a new belt but could it be a timing issue? If anyone has ideas, feel free to share! Thanks.

[mickthemaverick]

Have you checked that the throttle is not sticking just a tad open?

[Pete_D60]

When you connected everything back up after the engine swap, are you sure throttle cable routing was the same? Possibly the cable is restricted and not free to fully release the throttle.

Try disconnecting the cable from the throttle body and see if the idle drops - if it does, routing sounds like the problem.

[Nadzag]

It is drive by wire, so there's no cable. The throttle valve is a bit open yes, but what's causing the ECU to force it a bit open? Do these intake manifolds crack easily?

[mickthemaverick]

Maybe your throttle position sensor is playing up, have a look at this video: You may get some ideas from this video, the throttle calibration starts at just after 5.5 mins.

[i5xp]

Is the battery good? I've heard some ECUs increase idle when voltage is low, maybe some corrosion on wires or fuses? Have you had a Lexia on it?

[ozvtr]

I do not know how the engine ECU determines the idle speed. But I assume that either;
1) it is fed back from the crank angle sensor and uses the actual RPMs of the engine to adjust the position of the butterfly.
2) it is determined solely by the position of the butterfly as reported by the two potentiometers inside the E-throttle. I.E. It just goes to a certain spot and stops.
For the kiddies playing along at home, there is no "idle stop" for this throttle. It is driven from fully closed to fully open by the engine ECU. And it does NOT use a classic DC motor and gearbox!!

It should be possible to remove the air filter and push on the butterfly, while the engine is running. If the butterfly will not close it's possible it's stuck. Under normal circumstances there is a spring that returns the butterfly to fully closed when power is removed from the throttle body. You could also just look in there with the engine off? If the butterfly doesn't fully close that may explain something. The butterfly is driven by the engine ECU and you should be able to move it. But if the throttle is powerful enough, you may not be able to open or close it as the engine ECU will be fighting you. I have not had the reason to do this, so I don't know.
I would not hold the butterfly against it's will for too long as it is driven by the engine ECU and you don't want to blow up the driver transistors!
If the butterfly IS fully closed with the engine running you definitely have a vacuum leak!
If the butterfly is partially open and closing it does not shut down the engine, again you have a vacuum leak!
Otherwise the engine ECU is driving the butterfly open too far for reasons that I cant explain.

[ozvtr]

D'oh!!
After thinking about it, there is bypass air from the front of the throttle via the PCV on the top of the rocker cover to the inlet plenum!
If the butterfly were completely closed you would still get air into the engine! Is that what determines the idle? This air bleed?
Try blocking the throttle off completely at idle and see what happens.

[Nadzag]

Is the battery good? I've heard some ECUs increase idle when voltage is low, maybe some corrosion on wires or fuses? Have you had a Lexia on it?

Battery should have enough voltage and it has 640A. Might check the wires and grounding though.

[Nadzag]

D'oh!!
After thinking about it, there is bypass air from the front of the throttle via the PCV on the top of the rocker cover to the inlet plenum!
If the butterfly were completely closed you would still get air into the engine! Is that what determines the idle? This air bleed?
Try blocking the throttle off completely at idle and see what happens.

I tried that before and it just shuts down when covering the throttle body. I thought maybe air entered through the PCV. Its really strange, today it was staying stable at around 1.8k rpm while stopping at lights when test driving. And yesterday 1.5k rpm although it was idling stationary in the garage.

Also when cruising with no acceleration, the rpms hang around that same rpm range 1.5-1.8k, cruising like that. They don't drop below only in the higher gears it can drop to 1-1.1k rpm.

I will continue to look for vacuum leaks. I am really suspecting the intake manifold.

[Nadzag]

PROBLEM FIXED: thin metal U shaped rod connected to the accelerator pedal was bent forward, which caused the pedal to not fully return to the idle position. So the pedal was blocked at 18% throttle.

Always check the simple things first fellas

Thanks for your input.

[mickthemaverick]

I refer you to my first post up above!!

Have you checked that the throttle is not sticking just a tad open?

[ozvtr]

I tried that before and it just shuts down when covering the throttle body.

Thanks for letting me know about that. I would have assumed that bypass would have kept the engine going. FYI, that shows there are no vacuum leaks!

I will continue to look for vacuum leaks. I am really suspecting the intake manifold.

If you did not find the piece of metal you would have been stuffed as there is actually nothing wrong!! Therefore nothing to find.

[Nadzag]

I refer you to my first post up above!!

Have you checked that the throttle is not sticking just a tad open?

For some reason I thought you were referring to the actual throttle butterfly valve sticking rather than the pedal itself. Thanks for your response mate. And thanks to everyone else.