My 2003 Ford Focus 2.0 has developed a rough idle without a check engine light (CEL). This is an easy fix that anyone can do themselves with a few simple tools.
There are eight parts to check that can cause a rough idle with your car.
- Dirty Idle position valve – (IAC or IPV) very common
- PCV valve or faulty hose – common
- Vacuum leak
- DPFE fault- very common
- Mass Airflow sensor dirty or failed – common
- The throttle position sensor is faulty.
- Spark plugs, leads, and coil.
- Head gasket Coolant leak into a cylinder – Expensive repair not common.
- Bad Vibration caused by worn engine mounts.
Each will cause your car to splutter in the idle position. Usually when your car warms up the idle will improve.
Ford Focus has a history of developing cold rough idles. This is a well-known fault that you can repair yourself. Don’t take it to the mechanic, it will cost you hundreds. Fix it yourself. So let’s go over how to repair each of the 8 idle faults.
Table of Contents
- 1 1. Car idles rough but drives smooth fix.
- 2 2. 2003 Ford Focus Mass airflow sensor clean. (MAF)
- 3 3. Ford focus rough idle no check engine light check the PCV
- 4 4. Check for engine vacuum leaks.
- 5 5. Check the Differential Pressure Feedback of EGR
- 6 6. 2003 Ford Focus Spark plugs, leads, and coil.
- 7 7. Throttle position sensor fault
- 8 8. Head gasket Coolant leaks into a cylinder
- 9 9. Bad vibration Worn Engine mounts
- 10 Conclusion.
1. Car idles rough but drives smooth fix.
This is a common problem with older cars. Because the car idles rough but drives smooth points to an air/fuel mixture problem.
The first part to check is a device called the Idle Control Valve (ICV) (IAC) or Idle air control valve. This little air solenoid will open and close the air mixture going to the engine during an idle condition.
The problem is over time carbon and other dirt particles get stuck in the Idle control valve causing the valve to stop working in either the open or closed position.
If it is stuck in the closed position you will get a rough idle, engine shake, and the car may even cut out and stop. If the Idle control valve is stuck in the open position you will get a fast-revving engine in the idle position. Both conditions are not good but will cause the car to run smoothly when you start driving fast.
Another problem could be worn motor mounts. It is best to clean the Idle control valve first to see if that fixes the shake. Motor mounts can then be replaced if the engine shake continues.
Ford focus rough idle fix
To repair the Idle control valve you can either repair it or replace it. I prefer to repair the valve as it only takes a 1/2 hour to remove the valve and clean it out. It is easy with a second person to help you.
Start by removing the MAS airflow sensor cable. The electrical cables are clipped into place so press down the tab and remove the electrical socket.
Take apart the air filter box and tubing to the engine throttle valve.
Remove the PCV air hose to give yourself more room to work.
Pull out the electrical connection clip that is attached to the idle control valve. It is tucked behind the manifolds and the engine.
Use an 8mm socket to undo the 2 bolts. There is not a lot of room so if you are having trouble you can jack the car up and come up from underneath. I ended up using an 8m ring spanner from under the car to undo the bottom bolt.
Clean the idle control valve using carburetter cleaning solution spray. Keep the ICV in the upright position so that the dirt runs out of the air holes and not into the electrical solenoid.
Use a flat-blade screwdriver to push the idle control valve up and down. make sure it moves freely. Leave it out to fully dry for 1/2 hour before reinstalling.
Testing an Idle control valve.
Once you have cleaned the idle control valve with carb cleaner be sure to test that it moves freely. I like to use a flat blade screwdriver to move the plunger up and down. It may only move 5mm this is normal.
I also like to test the Idle air control valve with a multimeter. Set the multimeter to ohms and put the probes onto the coil wires. You should get a resistance between 7 and 20 ohms. The idle control valve for the 2003 Ford Focus measured 9.6 ohms so the coil is fine.
If you are reading 0 ohms you have a short circuit and it will need to be replaced. You can get a new Idle control valve for the Ford Focus AC504 from most good auto parts stores. They are cheap to replace.
2. 2003 Ford Focus Mass airflow sensor clean. (MAF)
My 2003 has a Mas airflow sensor that detects the volume and temperature of the air going into the engine. This is important to get the correct ratio of air to fuel for fuel injection engines. You can get a new MAF sensor for 2000-2004 here.
The symptoms of a faulty mass airflow sensor are:
- The engine is hard to start or crank over.
- The engine stalls in the idle position.
- The engine sputters, hesitates, or cuts out while under load or idle.
- Hesitation and jerking during hard acceleration.
- Excessively rich or lean idling causing a rough idle.
- High fuel usage
- Excessive emissions from the vehicle
- Misfire at idle.
How to clean a MAF sensor?
Locate the mass airflow sensor on top of the air cleaner hose and unplug the cable.
Use a Torx tip screwdriver to remove the screws. On the 2003 Ford Focus, it was a T2 Torx bit.
Pull out the MAF sensor and use some Mass airflow cleaner to spray all of the electrical components. Only use a Mass airflow cleaner on the sensor. Any other products will leave a residue on the sensor which will cause an incorrect reading.
Mass airflow sensor cleaner ingredients
HYDROCARBONS C>=5, C5-6 RICH (<0.1% W/W 68476-50-6 270-690-8 >60% BENZENE)
CARBON DIOXIDE 124-38-9 204-696-9 5 to 10%
N-HEXANE 110-54-3 203-777-6 <2%
3. Ford focus rough idle no check engine light check the PCV
Another reason for a rough idle could be a dirty Ford Focus PCV valve. This is an easy check to do as you won’t need any tools. The PCV valve on a 2003 Ford Focus is located on the front right-hand side of the Zetec engine.
You can pull the PCV valve out and disconnect it from the vacuum hose. Clean the PCV valve with carburetter cleaner and give it a little shake. You should be able to hear a rattle. If there is no rattle replace the Ford Focus PCV valve.
Check the PCV hose that there are no flat spots. Start the car and check if the engine vacuum sucks in the hose. If it is not round it will need to be replaced. You can get a new PCV hose here from Amazon. This is the hose that goes around the back of the engine that often fails. It will go soft and collapse on itself.
Some of the newer PCV hoses come with heat insulation to help stop the pipework from failing due to engine heat.
4. Check for engine vacuum leaks.
If your car idles rough and shakes check for any vacuum hose leaks. Go over all of the hoses to make sure that they are pressed onto the fittings. If they have a hose clamp then test for tightness.
Often a vacuum leak will occur when a hose pops off or the rubber hose collapses on itself. This will cause the Ford Focus rough idle with no check engine light and misfire.
Rubber hoses will get weak as they overheat and cool down. Start the car and check over all of the hoses to see if they are expanding or contracting. This could indicate a failed vacuum hose.
5. Check the Differential Pressure Feedback of EGR
The Ford Focus has a DPFE system installed to help control its emissions. These fail over time and will need to be replaced. It is a cheap part and easy to be swapped out. If you have checked the Idle control valve, the MAS airflow sensor, and the PCV valve the next thing to check is the DPFE.
What is a DPFE?
A DPFE is a sensor that refers to the process of the system actually sucking exhaust gases back into the engine for re-burn purposes. The DPFE will help to reduce the total amount of pollutants emitted by an engine as a portion of the exhaust is sent back into the intake manifold to be reused.
The DPFE sensor is a critical component of the exhaust gas recirculation system. DPFE means Differential Pressure Feedback of EGR.
Ford Focus DPFE sensor where is it located?
In a 2003 Ford Focus, the DPFE sensor is located on the top right-hand section of the firewall. It has two vacuum hoses going to it as well as an electrical connection. These can’t be repaired so if you suspect that it is faulty it is best to replace them.
6. 2003 Ford Focus Spark plugs, leads, and coil.
One of the first things I had done was replace the spark plugs. In fact, it is part of the yearly service. Leads can fail over time as well as the high voltage coil.
Most often these will cause problems while driving. A quick check is to start the car and pull each spark plug lead out one at a time with the engine running. This will show up in a change of conditions if the plug is good.
7. Throttle position sensor fault
The throttle position sensor is located on the throttle body. It gives a signal to your car’s ECU about what position the throttle is open to.
These are very reliable and I have only seen a few go bad. These are easy to test. If you have a multimeter or access to an OBD2 scanner you can check the value of the throttle position sensor.
These sensors are designed to show 0.9v at a closed position and 5v DC at a fully open position.
There are 3 wires going into the throttle position sensor they are.
- Ground – Negative
- Signal – 0.9v to 5v
- Active 5v – Positive
Use a multimeter and a sharp point probe to stick into each cable to check its electrical condition to the ground. Once to find the signal and ground place the multimeter into DC volts and measure between these two wires.
Have someone press the gas peddle down slowly and even. Watch the voltage rise from .9 to 5v. If it is erratic or stuck at 0v you have a bad throttle position sensor.
Another way to check the Throttle position sensor is to use an OBD2 scanner. I have a Bluetooth OBD2 scanner for use on my Yamaha MT07. I also use the Torque mobile app for Android to read the ECU values. The great thing about Bluetooth OBD2 scanners is you can use them on any vehicle or motorcycle you own.
Information is displayed on your smartphone and you can check engine fault codes. If required you can reset and clear the engine fault codes. This will clear the (CEL) check engine light.
If you watch the Torque live readings you will find the throttle position readout. You can see it live on your mobile phone.
8. Head gasket Coolant leaks into a cylinder
If coolant is leaking into one or more cylinders because of a failed head gasket then this is a major problem. The cost to repair a head gasket can be over $1000 dollars depending on the type and size of the engine.
I would try to repair the leaking head gasket with a product called K-Seal (Amazon). It worked for my car and it is the go-to product for many on-the-road repair mechanics.
K-Seal works by adding it to the coolant system and it finds its way to the leak. It plugs the leak and goes hard. It is safe to use on all engines and radiators.
If you are losing coolant and you can’t work out where from, then put some K-Seal into your radiator it will fix your issue. You can read more about how to fix coolant leaking from your engine block here.
If your engine head gasket has completely failed or the head is warped then I’m afraid some major engine work will need to be done. Try the K-Seal first as you may just have saved yourself thousands.
9. Bad vibration Worn Engine mounts
Another problem can be worn engine mounts causing engine vibration on your Ford Focus.
There are 3 engine mounts that you should replace after 200,000km. These can cause engine shake and vibration that can show up as a rough idle. Check out the procedure here on how to replace the engine mounts on a 2000-2004 Ford Focus due to vibration.
There are so many reasons a Ford Focus has a rough idle with no check engine light. But if you go through all of the possibilities mentioned in this post you will be able to repair the problem.
Sometimes it won’t be just one fault but a combination of many issues. I ended up doing all of the 8 steps mentioned in this article to fix my misfire at startup. I am happy to report that my Ford Focus now has a steady idle.
Now that my car is not vibrating anymore I can finally get around to upgrading and installing a Ford Focus Android Stereo. I’m in need of some sweet tunes.
Good luck fixing your Ford Focus misfire at idle. It has taken me a few weeks but it is finally sorted out.
I am a qualified Industrial Electrician for the past 20 years and I love to share my knowledge on home repair and maintenance jobs.
I love fast toys like Motorcycles, Cars, Jetskis, Boats, and Computers so writing about them is easy. Working on them is fun.
To keeps costs down I do all my own mods, repairs, and servicing. These skills I want to share with everyone. DIY is a skill everyone can learn.