VR6 drops revs when cold

[mookie 0]

I'm having a bit of an issue with my Corrado VR6. When the car is cold, until I've driven it for a couple of minutes, the revs will drop to about 450-500rpm if you dip the clutch. It never actually stalls, but the sudden drop in revs can sometimes stick for a couple of seconds before they slowly climb back to what they should be.

 

This never happens when the car is hot. In normal driving it runs fine, no problems or drop in performance.

 

On VAGCOM it returned a 00533 error (Idle Speed Regulation - adaption limit exceeded) - http://wiki.ross-tech.com/wiki/index.php/00533 - it says bad fuel economy, but mine seems about right for a VR6, and as it only happens when cold I'm assuming the rest of the time nothing bad is happening as a result (would that rule out injectors?).

 

I've tried to work my way through as many of the possible suggested causes, with no luck. So far I have done the following:

 

- replaced the blue temp sensor

- carb cleanered the ISV

- tried a second alternative ISV

- deleted the ISV damper box in case of air leaks

- deleted the PCV and associated pipework, also in case of air leaks

- sprayed carb cleaner over all vac lines with the car idling, no change in engine note, so assuming no air leaks

- removed all air intake pipework after the MAF, inspected, can't find any holes or splits

- ECU reset (twice)

- VAGCOM suggests the lambda is fine, returning the correct value

- inspected throttle body, looks clean as a whistle (worth removing and cleaning anyway?)

- checked air filter (standard airbox) and it's clean and new looking

- unplugged MAF, engine cuts out when idling (suggests it's OK?)

- unplugged the ISV and engine idles at something like 1500rpm (suggests ISV and connections work?)

- throttle damper checked, throttle isn't slamming shut

- readjusted throttle cable in case it was too tight etc...

- disconnected and cleaned most electrical connectors, including the big multiplug loom connector on the engine

 

Any suggestions?

 

I'm really struggling to figure out what to do next.

Edited August 14, 2012 by mookie

[dumptyboy 0]

I would try changing the MAF for one that you know works fine, as the MAF may still be faulty! Disconnecting it will stall the engine even if it works perfectly or if its faulty in my experience.

[mookie 0]

I've now tried a known working MAF with no difference at all... Toyotec over on ClubGTi has said it's probably an air leak post-throttle... but after deleting the ISV damper and replacing some of the throttle/ISV pipes, i can't see anything else to check? I've tried spraying carb cleaner on the various pipes and joints, with no change in engine noise to suggest a leak. Really tearing my hair out now.