Paddlekey

Ok - I've managed to fix it! Here is what was NOT the cause of the problem: - Throttle Body - MAF sensor - DME - Wiring loom (I had already changed the throttle body and had checked the wiring between the DME and throttle body connector) Today I did the following: a. Checked that the relays in the rear trunk (DME and Ignition) were seated ok - they seemed to be b. Connected jump leads from another car to the Porsche battery - my battery has completely died a few times over the last year (the car is used fairly infrequently) c. Turned the ignition key to position 2 (dashboard lights on) and then off about a dozen times (fairly quickly) I did a. because I wondered whether the DME was being powered up correctly - there are a lot of posts on the web about poorly manufactured Porsche relays (which have a habit of failing). I'm not convinced this solved the problem (I could hear the relay clicking when the ignition key was turned on), but I'll probably change the relays as they're cheap to buy and it will be useful to have a spare one in the car. I did b. because I wondered whether the battery might be 'on the way out' - I was concerned that the battery voltage might be low and that this could cause the DME a problem. I checked the voltage across the Porsche battery with a multimeter (about 12.2 V) - not significantly low, but the battery in the other car was 12.8V. Again, I'm not convinced this solved the problem - I still couldn't hear the throttle body motor when I turned the ignition key on. I then tried c. and on about the 12th time I left the ignition key in Position 2 (on) - this time I could hear the throttle body motor running! Definitely a good sign, so I turned the key further to start the car...full revs, no limp mode, no poor idle, no flat spots...Christmas had come f'kin early!!! With the engine running I used the Durametric to clear the codes. I then turned the engine off and started it again...all still ok....did this a couple more times to check....problem solved. Later I ran another Durametric test - no dreaded P1502, everything ok. I have no idea why the 'ignition cycling' fixed it - could it be a faulty battery (will fit a new one tomorrow), or relay (will replace it when I get a chance) or ignition key barrel (unlikely) or perhaps the DME was in some 'fault state' and the power on/off corrected it (unlikely as I had previously disconnected it for a day which would have reset the DME)? However, I know that Porsche Guildford wanted to start by fitting a new throttle body (£1500 just for the part - identical to a new Bosch one that I bought online for £370), would probably have then recommended fitting a new MAF sensor (£600 just for the part - identical to new Bosch one at a local motor factors for £200), and might then have recommended fitting a new DME (god knows how much that would have cost from Porsche....). I'm guessing that I didn't need to buy the throttle body (or pay £70 to get the DME tested), but who cares - I'm still on a high from getting the car working again! (Actually, the engine is responding brilliantly, so perhaps a new and clean throttle body did make a difference) I also purchased a Durametric tester - well worth the money as I wouldn't have known it was a P1502 fault otherwise. I hope the above helps someone else....and saves them 2 frustrating weeks trying to work out what it could be! Regards, Nick.

Hi Nick,

I had the same problem. Took it to Porsche, they swapped throttle body, etc and then they recommended I take the DME to a local repair center.

I had a look  inside the DME and saw one of two electrolytic capacitors leaking electrolyte. I asked the repair center to replace both caps,

(100uF 40V). They said they found two poor connections in the DME and replaced the caps, they tested the unit and claimed its ok.

I installed it, same problem. I then decided to do the ignition thing, by turning the ignition rapidly on and off for about 20 times. Then stared the car without waiting and was ok! I then turned off the ignition, waited a while, turned it back on, I could then hear the throttle body do its thing.

I think it could be a poor relay connection on start up? For now its ok, but I will check what relays are involved during start up.