Help needed with poor running

[Mojo_Brother]

Hi,

I have a 98 C2 3.4 with a poor running engine.

What happens is when the car is fully warm, with the oil pressure gauge at 1 the entire car shakes and a noise like a rattly dual mass flywheel is present. I push in the clutch the rattle stops but the engine still runs poorly. When revs are applied or when driving the car behaves normally.

I have replaced - the dual mass, clutch, AOS, plugs and coils and to be honest am at a loss. After replacing the plugs and coils the car ran perfectly, for a day.

I've had a random multiple misfire code twice before. Once after heavy rain (hence thought to replace plugs and coils) and once had the code after a DME reset (battery removal).

Need advice on how to resolve this as losing patience and concerned there's a major issue.

Thanks guys

 

[Mojo_Brother]

My only idea is we found that the spark plug tubes had leaks, not having the parts we replaced the plugs and coils only and cleaned it up with an idea to do the tubes later. Could these tubes cause a misfire?

 

[The Baron3]

Have you had someone who knows how to use a plug in diagnostic tool to look at all the potential issues?

 

[Mojo_Brother]

I have a diagnostic tool as do some friends that have repair garages. It very rarely throws any codes though. I've had two codes out of it. One for a random multiple misfire and another for a cylinder 1 misfire. I'm going to look for visible oil around plug tubes today and do a DME reset to encourage some codes. Will post any results.

I have also rebuilt the alternator and replaced the voltage regulator as at times before had low volts on the car's gauge.

Other info the car has done 108k miles but had a replacement short block in 2005 around 60k.

 

[Alex]

What's the tickover like when it's doing this? Are the revs jumping around 600-800? If you switch the aircon on does it get and better?

 

[deMort]

A fault code for a misfire on no.1 cyl means that cylinder has gone past the expected input it should supply and the dme recognises that cylinder is pretty much not generating the power required .. a misfire ..

A general misfire can indicate that other cylinders are close to the limit but not past and as such it does not generate a fault code saying cyl 2 or 3 .. or any of the others to be fair .

Early car so only vario cam .. it's possible this is faulty .. and probably bank 1 due to the code No.1 misfire ..

With a tester i can disable the vario cam , i will get a very poor running car or it will stall if its working .. this will prove if its ok ..

Caveat is sometimes a car just wont respond to this tester input .. i don't know why .. some do .. some don't ..

So if not .. the car at temps this fault happens and at idle the car should shake a bit .. the engine will feel a bit off .. that's an indication .

If we go down the route of a single cylinder misfire then we have compression , ignition and fueling .. you have changed the coil / plug so left with wiring .. i doubt it , compression again i doubt it but would check or an injector .. rare but possible .

It's basically a case of eliminating items until you come to the answer .. a pain .

EDIT..


A leaking plug tube wont cause a misfire .

 

[The Baron3]

What's the tickover like when it's doing this? Are the revs jumping around 600-800? If you switch the aircon on does it get and better?

I've got a similar fault and have changed the MAF the ambient engine temp sensor and had a Terra Clean.

When hot it sometimes cuts at idle, if I switch the air con on it helps with the jump revs.

It did throw up the variocam solenoid when checked but when put on the diagnostic you could switch it on and off, so don't think it's that.

My car is booked in with Lee at Cotsworld Porsche on Monday I will keep you posted.

 

[deMort]

Early cars also have an idle stabilisation valve .. a partial blockage in this or it sticking will cause a poor idle ... as will a vario cam issue .

 

[The Baron3]

Early cars also have an idle stabilisation valve .. a partial blockage in this or it sticking will cause a poor idle ... as will a vario cam issue .

Thank you for your input for both myself and the OP, I've not heard of this stabilisation valve, I will get them to check that out.

 

[deMort]

As below .... idle valve .

 

[The Baron3]

Although my car is a 1999 it's the C4 so it is not cable throttle, so not sure it has that part, will have a look in the morning, but thanks for the pic

 

[Mojo_Brother]

Thanks for all the responses, it would seem the car has adapted to it's new spark plugs and coil pack and the very rough idle is now only slight. Idles at 700, occasional bounce up and down 50 rpm here or there, which i think is normal for an early cable throttle car, especially with 100k miles. Alex - it does smooth out more so with the AC on.

My main concern is the brand new LUK dual mass still rattles when the car is hot in the same way the old one did... how is this possible? I've read in places this is normal for these cars but usually the chattering noise from a flywheel indicates it's time to change.

The chatter goes away when the clutch is pushed in and I've heard many rattly flywheels so definitely that's what it is.

 

[Mojo_Brother]

For reference does anyone have a video of a 996 3.4 idling well? :lol:

 

[deMort]

If you clear a fault code in the DME then the adaptations are reset to zero .. as such the car has to learn again the small imperfections in the engine .. a small air leak here , an injector not quite perfect etc etc .. roughly 50 miles and it will be back to compensating for issues .

These cars are actually very good at compensating and maintaining optimal running ... To the point even a large air leak or a sensor failure can be compensated for with no eml .

Eml on is more based around items that will affect emissions and not so much as a faulty sensor .. a faulty cat for example whilst not making a difference to the running of the car will trigger an Eml ..

A maf giving an incorrect reading wont .


Flywheel chattering .. both the old and new have done this i assume ... as such i kinda doubt it's anything to do with this ..

Offhand i would say a misfire , solid engine mounts , solid or modified gearbox mount even the crank damper or pulley .. (not seen that though) ... will all cause this .. misfire and an engine judder with the other 2 being that they transfer more engine noise to the cabin .. pulley and vibration , my thoughts anyways .

Bit difficult to go much further without seeing the car i'm afraid so just posting what i can .


ref The Baron3 , E Throttle and it wont have an idle valve so it won't be that .