Revolution(s) Calling.....

[JuliusF]

My 98 C2 engine seems to have developed a stutter between 2500-3000 RPM, a split second dip in power, then recovers - very much more noticeable when its cold.

Thought it was the Tip box changing up roughly to start with as initially it was more noticeable in full auto mode, but I'm erring towards the engine not escalating smoothly now.

Less noticeable when the engine is warm and when using the tip mode buttons to change up and down, but its still lurking in the background.

Just had it serviced, no error code clues at the time - did have new tip oil (96K service), but otherwise a clean bill of health.

Thoughts please?

Cheers.

J

 

[andywill]

Hi Julian
I'm sure Richard will be along soon,but my thoughts would be, possibly MAF or lambda sensor, are you using Shell? if not give it a dose of V power.

 

[Gordon Attar]

Was it a major servixe including spark plugs? One could be faulty. Coil packs another source as well as

 

[JuliusF]

Thanks - Plugs were done 6000 miles/12 months ago -although I'd have thought plugs or coils woudl have been more erratic/presenting all the time - this problem is consistently in the range 2500-3000?

 

[Richard_Hamilton]

Get a diagnostic check done, otherwise you are shooting in the dark. As well as the above (plugs, lambda sensor, coil pack, MAF, etc, etc) I'll throw a Variocam solenoid as a possibility. A diagnostic will give you more of a clue. It needs to be a Porsche specific tester too, as generic testers don't always show the Porsche specific codes, particularly on cars with DME5.2.2 like the 1998 C2.

 

[JuliusF]

Had this investigated last week, and the tiptronic (auto mode) was indeed throwing error codes, but diagnosed (reasonably) due to inconsistent torque through the rev range between 2500-3000.

Although there were no air mass sensor faults it was suggested by my indy I change it as the problem was consistent with their previous experience.

So we changed it (fat end of £300 fitted) and....... it helped a bit (grrrr!) - smoother auto changes generally and hitting the 7,000 red line much more smoothly, so I think it was part of the problem - tiptronic button shift seems pretty much fine by the way.

Stumped now - stuck with the same issue (but to a lesser extent) - you can feel the revs are all over the place between 2,500 -3,000 especially when cold - potter around below 2500 or toe it up above 3,000 and its sweet as a nut.

Any suggestions - could a remap help I wonder? Or would a rolling road test give us any clues?

J

 

[Richard_Hamilton]

Did you make a note of the Tiptronic error codes?

 

[JuliusF]

Hi Richard,

Sorry I didn't note it down - Just a single code, i do recall on the diagnostics screen it said something like "torque converter clutch fault" - but this doesn't feel mechanical - more electrical/electronic (almost like bad points if it were an old car!) - there is some sort of solenoid system on the tip box I understand - I wonder could it be something in that direction?

Is there a list of fault codes I could reference by the way?

J

 

[Richard_Hamilton]

Here is the info on Code P0740, which is the same as your description. The clutch is the torque converter lock-up clutch, which is controlled by a solenoid valve on the valve block inside the box. First thing to do would be to get the level checked using the workshop manual procedure.

P0740
70, Torque converter clutch fault
The difference between transmission input speed and engine speed is monitored

Diagnosis conditions
• ATF level OK
• ATF temperature 40° C to 95° C
• Selector lever position 'D' or 'M', 2nd, 3rd, 4th or 5th gear
• Gear engagement completed
• Engine speed > 1400 rpm

Possible fault cause
? ATF level too low or too high
? Torque converter clutch is faulty

Edit:A bit of info about the Converter Lock-up Clutch:

 

[JuliusF]

Superb info as always Richard - much appreciated. J