Kia Optima EGR Replaced, Still Losing Power: Case Study
Kia Optima 1.7d (2012 – 73,046 miles)
Reason for booking in…
‘Engine shakes quite abit when idling, I’ve got loss of power with not much acceleration especially going up hill and it used to fly up hills, I’ve had EGR valve replaced but it’s not restored my power so I think maybe a clean would do it some good and fix the issue.’
Initial inspection found no obvious issues in the engine bay with no excessive rattles and shakes, but a lot of vibration from the carbon present.
Initial code read found a historic code for…
P0403 EGR Control Circuit
Live data showed all temperature and sensor values showing acceptable figures.
Why Was the Kia Optima Still Losing Power After the EGR Valve Was Replaced?
A Kia Optima with the EGR replaced but still losing power is a familiar pattern to us, and it’s exactly what turned up on this 1.7d. This car had already had a new EGR valve fitted after the P0403 EGR control circuit code came up, but the vibration at idle and the drop in power under load hadn’t gone away.
That’s because replacing a faulty EGR valve doesn’t always solve a loss of power on its own: carbon build-up in the intake and EGR system can restrict airflow and unsettle combustion long after the valve itself has been swapped out. As Professional Motor Mechanic explains, excessive carbon build-up inside the EGR valve and cooler is the most common cause of EGR-related faults, and it’s made worse by repeated short journeys at low speed. That’s exactly the build-up an engine carbon clean is designed to remove, which is why this Optima only smoothed out once the clean itself was carried out, not from the EGR replacement alone.
On with the clean and it soon smoothed out, quietened down a lot and by the end it was quiet, smooth and responsive again.
Review from the owner…
‘Adrian was very polite and great to talk to, gave me loads of information which I have found useful, after the carbon clean my cars running superb no engine vibrations inside car anymore, engine smooth and quiet especially at higher speeds and more responsive acceleration, can’t recommend enough will definitely be using this service again ‘
Frequently Asked Questions About Kia Optima EGR Replacement and Power Loss
I’ve had my EGR valve replaced but I’m still losing power. What could be wrong?
A replaced EGR valve fixes the valve itself, but it won’t clear carbon build-up already sitting in the intake, EGR cooler or combustion chambers. That build-up can keep causing vibration and a loss of power until it’s removed with a proper engine carbon clean.
Why does my Kia Optima vibrate or shake at idle?
Vibration at idle on a diesel like the Optima is often linked to carbon deposits disturbing smooth combustion. Once the excess carbon is cleaned out, idle quality and smoothness usually improve straight away.
What does the P0403 EGR control circuit code mean?
P0403 flags a fault in the EGR valve’s control circuit, often triggered by carbon fouling affecting the valve’s movement or signal. It can appear even after the valve has been replaced if surrounding components are still carbon-clogged.
Will an engine carbon clean fix loss of power going uphill?
In many cases, yes. Carbon build-up restricts airflow and reduces combustion efficiency, which is felt most under load, such as climbing hills. Removing that build-up with a professional carbon clean often restores lost power and responsiveness.
