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Rough idle & Hot Start issue - VR6 12v

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Hey all, 


Looking to tap into some expertise knowledge. I've been researching various threads online and made maintenance changes to my car to try and get the bottom of my slightly rough idle and warm starting issue.


History of the car


95 Corrado VR6, 150k, full service history (serviced every year). No error codes (except ABS = pump) 




Idle is intermittently (more so than not) a bit rough. VCDS sees it fluctuating around 40rpm say 640-680rpm on idle. Attached is the VCDS log, this reading was done a few months ago but idle drops every say 3 seconds however it recently feels more frequent. I'll try and get an updated reading. Can't see it on the tacho but can feel it in the cabin.


Car starts fine from cold but when warm it cranks and cranks (10+) before firing up.


Drive fine, fuel economy seems reasonable, tail pipe a bit sooty though. Doesn't stall even though the idle is weird and feels powerful but it's always been like this since owning.


Parts changed


Cam sensor (fault code)

Crank Sensor

Thermostat  + the 3 sensors

Rad fan switch (fans were not working properly)

Fuel Pump Relay

Spark Plugs

HT Leads

Coilpack (had a crack in it)

I've installed a one-way valve on the fuel line from the pump (corrado forum -> a few people have done it, some found it cured hot start issue - I didn't get the logic but it was only a few quid).

New Fuel Filter

New FPR valve

I've sprayed carb cleaner around hoses to search for vacuum leaks (is there a better method than this?)

New PCV valve (old one was cracked)


I'm left with the fuel pump itself and injectors. One avenue to investigate is leaking injectors - looking at the bolts around the manifold it doesn't look like they've ever come off so believe injectors have never been serviced. I've read leaking injectors could cause hot start issues and a rough idle. Likewise with the pump it's VDO and was caked in rubbish so guessing it's original too: it's pretty silent in operation, could that mean it's weak?


Does anyone know how to use VCDS and measuring blocks to analyse injectors or the pump? Is there anything else to check?


If it's not these things I fear it could be mechanical but the car doesn't use oil (no smoke on idle or whilst driving - i've been followed by the wife to check) and isn't using any water.





Edited by pfnsht

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