Mystery starting issue 1.8 GTi PB- help! July 12, 2025, 10:03:33 AM Looking for help with an ongoing issue.My 8v GTI digifant has an ongoing starting issue. It takes a good 5 seconds turning the engine over before it fires and then it runs really lumpy. After a little throttle for a few seconds it clears and runs great. Car pulls really well when driving. No smoke etc and gets good MPG when I’m cruising along.Car has had a full diagnostic and tune. Plugs, rotor, cap, leads and coil all good. Recent new idle valve, both fuel pumps have been replaced and prime as you would expect. Battery has full charge and volt meter is showing good volts when running. Throttle body switches are working and lots of the connectors have been cleaned. No vacuum leaks. Blue temp sensor tested. Injectors have been tested and are in great condition.It occasionally starts fine, usually in the morning. When it’s been to the garage to check for known faults, with no solution found, it starts fine for a couple of days then the problem returns. If I restart the engine within a couple of minutes of turning it off it works fine. Engine was rebuilt last year by previous owner and has run fine until now. Good oil pressure on start up. In the recent hot weather with oil temp at 130c oil pressure at idle can drop to an indicated .6 bar but no oil pressure warnings on dash. My local specialist who knows these engines very well is now expecting an electrical issue.But I would love some input from other MK2 owners. Thanks in advance for any suggestions
Re: Mystery starting issue 1.8 GTi PB- help! Reply #1 – July 13, 2025, 09:16:38 AM Hi I am currently experiencing similar issues. I can start the car from cold fires straight away and runs perfectly. When the car warms up I have the same issue as you. I think the fault lies with the blue temperature sender I have ordered a replacement and am awaiting its arrival so can not say if that is the issue yet. Out of interest I ordered a hella replacement as I understand other makes are thought to be unreliable.
Re: Mystery starting issue 1.8 GTi PB- help! Reply #2 – July 15, 2025, 12:45:57 PM Sorry can’t provide any answers but wondering if either of you have managed to get anywhere with this yet?
Re: Mystery starting issue 1.8 GTi PB- help! Reply #3 – July 16, 2025, 12:15:58 PM Hi @ eddypeck I am still waiting for delivery of the sensor arrives tomorrow supposedly. Will say if its a fix or not.
Re: Mystery starting issue 1.8 GTi PB- help! Reply #4 – July 17, 2025, 07:38:10 PM I fitted a Hella blue temp sensor just incase the old one was causing the problem although it was tested. I also noticed that my battery was beginning to not hold as much charge as I would prefer so I changed it. It’s been a couple of days and so far it’s working fine but time will tell. After all the effort in trying to diagnosing the issue this seems to easy… 1 Likes
Re: Mystery starting issue 1.8 GTi PB- help! Reply #5 – July 18, 2025, 04:00:42 PM Hi monkey sadly blue temp sensor did not fix the problem for me. My issue persists car starts from cold perfectly ticks over at 900rpm when the engine is warm stop the engine and immediately restart and the engine revs up to1500rpm and drops to 500 rpm it does this 3 or 4 times before settling down to idle at 900rpm. leave the car off for a short while and it will not run without some throttle being applied it soon settles down and idles at 900rpm.
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