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Christophe126

Rough Idle ‘04 986

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Hi all,

My ‘04 986 has a rough idle (Fluctuates about 50rpm) but revs and drives fine, no engine light either. Engine light was on but went off after changing cam sensor. Have changed AOS, ignition coils, spark plugs and cam sensor, but still no luck. Any thoughts?

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Check your MAF sensor readings (IAT and mass air flow), replace if necessary , check fuel trims and clean the throttle body.

There is also change that it could be one of your lambda sensors but likely you would see odd fuel trim readings  on one bank only 

Both the MAF and TB contributed to uneven idle on my 986s. Replacement of MAF and a clean of the TB sorted it

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Very easily Accessible in the engine bay with the roof in service position, I advise using an OBD tool to check the values &/or unplugging the MAF and clearing adaptations to see if the idle improves 

The only thing to watch for is corroded screws (these were a real pain for me on both cars) and you need a security torx to remove it

your DME Software level and engine will determine which part number is needed if it's a 2000MY E gas car, best bet if it's this age is to remove and check.

If a 2.5 or a later 2.7/3.2 car , then it's fairly easy to determine which is needed without removal.

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Note, you will need a torx bit with a dimple in it, to remove the MAF screws.  Don’t know the technical name for the torx bit.

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My erratic idle was down to the idle sensor, if your cleaning the MAF and the TB then you may as well clean out the Idle sensor.

Failing the above you may have an air leak that will be harder to locate

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19 minutes ago, the baron said:

My erratic idle was down to the idle sensor, if your cleaning the MAF and the TB then you may as well clean out the Idle sensor.

Failing the above you may have an air leak that will be harder to locate

Only 2.5 has a separate idle control valve.

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2 hours ago, edc said:

Only 2.5 has a separate idle control valve.

Ahh, ok good to know. Mine was filthy as was the TB which cleared that fault up.

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On 1/4/2020 at 6:59 PM, Christophe126 said:

Hi all,

My ‘04 986 has a rough idle (Fluctuates about 50rpm) but revs and drives fine, no engine light either. Engine light was on but went off after changing cam sensor. Have changed AOS, ignition coils, spark plugs and cam sensor, but still no luck. Any thoughts?

I had the same trouble, tried all the standard recommendations but nothing worked 

I changed the 02 sensors. Problem solved

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Having just been through the pain of MAF problems, mine started by just fluffing a bit at idle and within a short period of time was misfiring and dropping cylinders all over the place.  Just a MAF clean (see online vids) might solve your problem as the hot wires may have become contaminated as it is it only fluffing a bit currently.  Simple test, disconnect the MAF and see if it runs smoothly on the default map without MAF inputs.  This will trigger a check engine light (CEL) to come on so only do this if you have a means of clearing it with a code reader as @naim22 has noted.

As for hollow tip Torx bits all the ones I had were cheap so I bought a set of decent Bosch bits from amazon and using an extension on a screw driver type bit holder has no big problem getting the screws out on a 2000 car with good tools.  I couldn't putt the electrical connector off the MAF whilst it was in position for some reason (It came off with little effort once I'd removed the MAF...). The problem I was finding was that an Allen key type on you tend not to be able to put downward pressure on to the screw head at the same time as twisting which possibly contributes to most of the burring out of the screw heads that people report.  When I fit the new sensor later today I'm going to put some grease in the screw heads to stop water sitting in them and corroding them.

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