Intermittent start issues

[matty8]

Hi, I'm looking for some advice as I've come to a dead end using up all the info gained from other threads out there.

My recently purchased '99 996 tiptronic (which has been standing for most of the last 10 years) is starting about 50% of the time, the rest of the time there is no crank, everything appears normal, just no crank! It may start in 10 minutes or 10 hours, but will start again at some point. It's pretty random, the only continuity is that if it has been running for a while after I leave it for a minute or two it wont start (no crank). Error code 5284 (electrical connection between TC and DME) is present when the non starting fault is present and not when its starting ok - this is all I have to go on now but don't know what to try. Maybe there's another ground lead I could test?
What else I know -
Its not the battery - new one measuring 13v, not exact spec but slightly higher Amp hours.
Its not the starter - bridging the relay will make it start
Its not the relay - have swapped them about, but when the problem exists there is less than a volt going to the relay, else full voltage
Don't think its the ground lead - engine casing measures full voltage, have cleaned the chassis end but not the casing end
Not the ignition switch - replaced that
Don't think its the tiptronic selector not being in park - its displayed on the instrument cluster
Don't think its the immobiliser - no error code and alarm light on dash goes off when key is turned in ignition after manual locking

Any knowledgeable advice gratefully received - TIA

 

Matt

 

[Loren]

What scanner did you use - that is not a Porsche fault code.

[matty8]

Its an Autel MaxiAP AP200 scanner