Passat intermittent start issue

[Simon86]

Hello,


First time poster,


I have had my Passat for over a year now, and I have done 15,000km and just clocked over 87,000km. I love the car


Car is a 2018 B8 passat with 1.8T 132kw TSi


Full-service history, new battery installed in the last 1,500km




I am having an intermittent start issue, where the car takes longer to crank, once this happens I know it will run but I know it's in limp mode I would guess, as soon as this longer cranking appears I get a P0687 code, if I drive the car in this behavior I will get a P0016, and P0658




I did stumble across it when I removed the ECM/PCM 658 relay from the fuse box in the engine bay for 30-60 seconds the car would then start and drive normally. So I assumed it had something to do with the relay and purchased a brand new one from my local dealer.


Fitted the new relay, and everything seemed fine for one day. Then the next morning on a cold start I had the same issue, longer cranking than started. I pulled out the relay and re-fitted and the car started like normal and drove normally.


Decided to drop the car off to my mechanic.
I had my mechanic do all sorts of tests including the battery/alternator readings are normal. The car won't replicate the above issues when it is in his position. Tested the chain tolerance on his computer and he mentioned the value the computer is aiming for is 15 and the car was giving 14.7-14.8


I got the car back running well for almost a week. He didn't do anything mind you.


Drove the car in the morning and the afternoon today. Return to the car later in the afternoon, and the car cranks a little longer than usual and starts. I immediately knew the car wouldn't drive well, kept the car going, and quickly plugged in my scanner (P0687) no codes till now as I have been checking it very often! idles well and seems normal apart from the longer crank times, however as soon you take off the car wants to bog down.


So I drove it around the block, for a few minutes assuming what you would call limp mode, drives and shifts gears smoothly If I am gentle on the throttle, as soon asi put my foot down it's like hitting a brick wall pulled over, and did a scan - still showing the P0687, and now I get an additional few codes P0016 as well as P0658. At this stage I still don't have any errors showing on the dash, no engine light light etc.


I pull out the ECM relay for a little bit put it back, car starts and drives like new again.


Why is it when the ECM relay gets pulled out and put back in after say 1 minute give or take. The car drives normally and starts normally.


If it was a Cam or Crank sensor, wouldn't this be a consistent issue longer starts for example? Could the ECM unit potentially be at fault or alternator just randomly generating high values?


My next plan of attack is to get the car towed to the mechanic when it happens and me not pulling out the ECM relay again and let him see it first hand.


Any input would be very much appreciated,


Thank you in advance,
Simon