BMW Rough Idle on Startup – 1998-2006 3 Series – M52/M54 Engine E46

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BMW E46 rough idle
BMW Rough Idle On Startup fix – 2 Hours
Repair cost 2

The BMW Repair Guide used this 2003 325ci for the following article.

Repair Summary
The following article gives detailed instructions on performing a rough idle repair on a BMW E46 3 series car. Even though we have used a 2003 BMW 325ci to perform this installation, this article can be applied to any E46 3 series vehicle with the M52 or M54 six cylinder engine (with minor modification), including the 323i, 328i and 330i coupe, sedan and convertible.

If your 3 series is showing rpm fluctuations when holding the accelerator at a constant speed, or if the engine rpm in your car repeatedly drops and then recovers when idling, then it may be time for a BMW E46 rough idle fix.

We say it in most articles we write, so excuse us for being redundant. But for many of us our BMWs are unfortunately getting old. Ok…insert your sad frowny face emoji here.

When Bimmers get over ten years old, its time to face the facts that many engine parts are going to need replacement, especially in the air intake system. The intense heat of the engine compartment, compounded by the age and “wear and tear” of the vehicle, plays havoc on the hoses, boots, gaskets and valves that make up your BMW’s air intake system.

A BMW E46 rough idle repair is a fairly simple job that requires replacing your DISA and idle control valves. If you are interested in what the DISA and idle control valves do, please refer to our rough idle repair article for the BMW E60 5 series where we go into a more in depth discussion.

The BMW Repair Guide recommends replacing both valves when fixing a BMW with a rough idle on startup. Since both parts have a maximum life span of approximately 100,000 miles, if one is failing most likely the other is ready to go as well. Do yourself a favor and spend the extra money and replace both parts.

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1. Idle control valve (required) – Replacing your idle control valve is an important step in curing your BMW E46 rough idle issues. Always replace the rubber grommet when replacing the valve.

2. DISA valve (required) Always replace your DISA valve when replacing your idle control valve.

3. Air filter (optional) If you haven’t changed your air filter in a while, now is a great time to do it. Help your E46 3 series engine breathe better with a fresh air filter element.

BMW E46 325i and 330i
BMW E36 323i, 328i and M3

3. Cabin air filter (optional) – Since you will need to remove the cabin air filter housing in order to do this repair, now is a great time to replace your filter. Replacing your cabin filter insures your new blower motor circulates clean fresh into the interior of your car. We give you several choices based on your budget.

The BMW Repair Guide makes every attempt to publish their repair articles with detailed step by step photographs, videos and written instructions. Since this repair deals with varying years and models, your vehicle may be slightly different than what is shown in the following steps and images. Some repairs may also require additional steps not covered in our articles like: removing covers from the engine and undercarriage, moving wires or hoses to access parts, cleaning and lubricating parts associated with the repair and performing general maintenance.
Section 1 – BMW E46 rough idle on startup

Repairing the rough idle in your BMW E46 3 series car requires replacing both the DISA and idle control valves and replacing them with new ones. Make sure that you take your time during reassembly to avoid any leaks in the intake system, especially when reinstalling the intake boot.

        1. Remove the right side engine cover using a pick and a 10mm nut driver as shown below.BMW rough idle on startup - remove the fastener caps from the engine covers BMW rough idle on startup - Use a 10mm nut driver to remove the left engine cover
        2. Twist the three spring latches counterclockwise to unlock and release the cabin filter cover.
          BMW rough idle on startup - Remove the cabin filter cover
        3. Using a torx T30 bit remove the three screws securing the filter housing to the fire wall. Remove the filter housing from the vehicle.BMW rough idle on startup - Remove the cabin filter hosuing
        4. The next step in the BMW E46 rough idle repair is to remove the intake muffler (air box) from the engine compartment. Use a 10mm nut driver or socket wrench to remove the two mounting bolts anchoring the air box to the body of the vehicle.BMW rough idle on startup - Remove the intake muffler (air box) mounting bolts
        5. Disconnect the Mass Air Flow (MAF) sensor.BMW rough idle on startup - Disconnect the mass air flow sensor.
        6. Using a flat blade screwdriver, loosen the hose clamp connecting the air intake boot to the air box.BMW rough idle on startup - Loosen the hose clamp securing the intake boot
        7. Remove the air box from the engine compartment.BMW rough idle on startup - Remove the intake muffler (air box) from the engine compartment
        8. Remove the vacuum line from the intake boot.BMW rough idle on startup - Remove the vacuum line from the intake boot
        9. Remove the DISA valve electrical connector. The release spring is on the back side of the connector.BMW rough idle on startup - Remove the electrical connector from the DISA valve
        10. Using a T40 torx bit, remove the two screws anchoring the DISA valve to the intake manifold. Grasp the DISA valve and carefully remove.BMW rough idle on startup - Remove the DISA valve mounting screws BMW rough idle on startup - Remove the DISA valve from the intake manifold
        11. Using a flat blade screwdriver, loosen the hose clamp anchoring the top hose of the intake boot to the idle control valve. Pull the top hose off of the idle control valve being careful not to bend or tear it (there is a screw below it we need to get to in the next step).BMW rough idle on startup - Remove the intake boot from the idle control valve
        12. Using a flat blade screwdriver, loosen the hose clamp anchoring the intake boot to the throttle body. Pull the intake boot off of the throttle body and remove from vehicle. You will notice from the photo below we damaged our intake boot during removal. This boot had 140,000 miles on it and ripped apart during removal. BMW rough idle on startup - Loosen the intake boot from the throttle bodyBMW rough idle on startup - remove the intake boot from the vehicle
        13. Disconnect electrical connection to the throttle body. You may need the help of a flat blade screwdriver to get it loose.BMW rough idle on startup - Disconnect the throttle body electrical connectorPull the plug from the throttle body
        14. Now it is time to loosen the engine wiring harness so the idle control valve can be removed from the manifold. Start by removing the top two T40 torx bolts.BMW e46 rough idle repair - Remove the two T40 torx bolts anchoring the wiring harness to the intake manifold.
        15. Next move down the wiring harness and remove the 10mm bolt using a nut driver or socket and wrench.BMW e46 rough idle repair - Remove the 10mm bolt securing the bottom of the wiring harness.
        16. Next, the bottom throttle body mounting bolt must be removed. Use a 10mm socket wrench with extension.Remove the lower throttle body mounting bolt
        17. Finally, remove the 10mm bolt anchoring the engine wiring harness to the idle control valve.BMW e46 rough idle repair - Remove the upper 10mm wiring harness mounting bolt
        18. Grasp the idle control valve and pull it out of the intake manifold.BMW e46 rough idle repair - Grasp the idle control valve and pull it free from the intake manifoldRemove the idle control valve from the engine
        19. Locate the idle control valve rubber grommet and remove with a pair of long reach needle nose pliers.BMW e46 rough idle repair - Remove the idle control valve rubber grommet Pull the grommet from the intake manifold.
        20. Remove the idle control valve mount by sliding the valve out of the rubber retaining sleeve. Note the position of the valve in the mount during reassembly.BMW e46 rough idle repair - Remove the idle control valve from its rubber mounting sleeveBMW e46 rough idle repair - Remove the idle control valve from the rubber sleeve
        21. Reassemble the vehicle using a new idle control valve, DISA valve and rubber grommet. Make sure the new idle control valve grommet is correctly seated in the intake manifold so you have a nice tight fit with no leaks.
BMW E46 Rough Idle on startup fix Finished
If you have any questions or comments, please feel free to contact us. And congratulations for Doing It Yourself!
The Repair Difficulty Level displays graphically how challenging the repair is, from easy to advanced. Easy repairs usually require very few tools, have short repair times and do not require jacking and supporting the vehicle. As the difficulty level rises, expect the repair to demand more time, specialized tools, and better understanding of mechanics to complete the job.
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