Porsche 928: Why Does My Car Idle Roughly?

This article applies to the Porsche 928 (1978-1995).

Your Porsche 928 should have a constant, steady, low idle. It shouldn't be rough or fluctuating. An idle problem is something you want to get checked out as soon as possible because it is certainly causing your 928 to not run at its peak. This includes lower gas mileage. Read on to discover the top four reasons that can be the cause of a rough idle in the 928.

Step 1 – What condition are your spark plugs in?

Old or bad spark plugs can cause a rough idle. If they are due for a change, you should change them since this might fix your idle issues. If you think they are okay, take them out and inspect them or have them inspected by a professional. Make sure your spark plugs are in good condition. On the same subject, make sure your spark plug wires are in good condition and preferably OEM. Aftermarket spark plugs are hit or miss in quality.

If your spark plugs are okay, continue on to Step 2.

Step 2 – Are you having fuel problems?

How old is your fuel filter? A clogged fuel filter can cause issues. If you don't know, consider replacing it. Or, if it needs replacing, replace it. Has your 928 been sitting for a while? Maybe it has bad gas; make sure it isn't. Also, have your fuel pressure checked out. Have a professional take a look if you are not certain about doing it yourself.

(Related Article: Porsche 928: How to Replace Fuel Filter - Rennlist.com)

If everything associated with your fuel is good, then try the next steps.

Step 3 – What condition is your catalytic converter in?

What condition is your catalytic converter in? A clogged cat can cause idle issues. If you have an older model and are unaware of the cat ever being checked out, you should have it inspected.

Step 4 – Has your MAF sensor gone bad?

A common cause of a rough idle on the 928 is the Mass Air Flow sensor in the intake tract. The MAF sensor is used to meter the air-to-fuel ratio based on the incoming air pressure in the intake. If this sensor is malfunctioning, it's sending the wrong signals to the engine's computer and will cause a rough running condition, usually at idle and full throttle. Have it inspected to make sure it is working well. If you need to replace it, check the simple things first before buying a new one. Is your air intake filter dirty? A dirty filter can cause a rough idle.

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