Rough Idle + fluctuating timing advance

[mattecoll]

Hi

Ive been looking into a rough idle problem with my 'new to me' '98 996. After ruling out a vacuum leak, replacing coils and plugs and cleaning the intake and maf sensor I took a look at the error codes;

P1340
1319, 1318, 1316, 1531
5283 (the car has another quirk where the tacho drops out for a few seconds inder hard acceleration, maybe related?)

Lots of googling last night led me to look at camshaft deviation values, my OBD reader only shows 'Ignition timing advance for #1 cylinder - is this the same thing as 'camshaft deviation for bank 1' ?? Am I right in thinking some ROW cars can only read bank 1?

The values I'm getting fluctuate between 4.5deg to 10.5deg at idle, then jump to a steadyish 38deg at around 3000rpm, possible failing IMS? (but been like this since I've owned it - 1k miles)

Also, I did find a few very tiny plastic pieces in the filter last oil change, so worn chain guides?

Should I panic, buy/borrow a durametric, or what....

TIA!
 

[JFP in PA]

Welcome to RennTech 

 

P1340 indicates the bank 1 exhaust cam allocation is not correct.

P1319, 1318, and 1316 indicate individual cylinder misfires

P1531 indicates bank 1 cam is not assuming the active position (possible bad actuator)

 

You have a problem with the bank 1 VarioCam system, which could be anything from a failing actuator to the cam itself being out of timing position.  You need to get the car scanned with a Porsche specific diagnostic tool (Durametric, PIWIS) which can not only see the actual cam angles in real time but can also test trigger the VarioCam system one bank at a time to evaluate how the actuators are working.  I would also consider not driving the car until you can get it evaluated as the engine really does not like running like this, and you could do more damage doing so.

 

[mattecoll]

Hi JFP! Thanks for the welcome.

I've read a few of your previous posts on this, but this more specific info really helps, thanks. I think I need to get use from a durametric if I'm to dig deeper into the issues. 

Would I be right in thinking the actuator would need to be stuck 'on' to give a rough idle - if its off surely it wouldn't affect the idle?

Could it be a faulty CPS seeing as my tacho drops out occasionally?

Whatever, looks like I'm back in the Landrover for now 🛻

[JFP in PA]

It would depend upon what position the actuator failed in; because these are hydraulicly operated devices, a small bit of debris in the oil, which you stated you have, can jam the actuator piston in a "partial" position, which drives the system nuts.  Usually, if the CPS is having issues, you get a P0336 code, but not always.  The device is a simple Hall Effect sensor, so if you disconnect the harness to it, you should see 0.8 to 1K ohms between pins 1 and 2 on the sensor plug, and infinite ohms between pins 1 and 3; if either is not correct, can it and replace it with a new one.

[mattecoll]

OK, so I have a Durametric and the Bank one is permanently on 24deg. I can't read bank 2 as this is a UK car. I have however tested switching each bank on and off - bank one makes no difference, bank 2 does (car nearly stalls then adjusts).

Does this confirm a jammed actuator?

[JFP in PA]

Yes.

[mattecoll]

Sorry for my ignorance, but do you know which part of the actuator gets stuck / jammed? I can see how its easily possible with Variocam plus, but not the earlier variocam like mine

[JFP in PA]

It is the plunger assembly in the actuator, and it is a very common problem:

 

[mattecoll]

Great, ok.... so can this be removed and freed up by unscrewing the solenoid to give access - i.e. not remove the assembly?

 

[JFP in PA]

34 minutes ago, mattecoll said:

Great, ok.... so can this be removed and freed up by unscrewing the solenoid to give access - i.e. not remove the assembly?

 

Nope.  Because you often need to replace the actuator, to do this, you need to lock the engine at TDC, remove the cam cover, cam shafts, the chains, and then the actuator.  This will require the use of cam retaining tooling, cam holding tooling, and reallocation of the cams (requiring special tooling) when putting it all back together.  It would also be an excellent opportunity to replace the two cam wear pads between the camshafts as these are considered a "consumable" wear item in these engines.  If it would help, Jake Raby and PCNA recently put out a video about just replacing the wear pads, but it gives you an excellent overview of the process and special tooling involved:  Raby/PCNA replacement of cam wear pads on 5 chain 996

[mattecoll]

Understood. I was just watching some of that video - great insight to the job without lifting a spanner. Thanks for your help here, I have a feeling I'm goint to end up doing both sides, plus the IMS etc!

[JFP in PA]

6 minutes ago, mattecoll said:

Understood. I was just watching some of that video - great insight to the job without lifting a spanner. Thanks for your help here, I have a feeling I'm goint to end up doing both sides, plus the IMS etc!

 

Jake has probably forgotten more than most of the rest of us combined know about these engines, so he is a trusted source.  You would be wise doing both sides, the IMS, the RMS, new plug tubes, etc. all at the same time; you really don't want to go back in there six months down the road.............😉