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Cling film.....more HP

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Here's one for ya...

Started the car up to warm it up this morning (been freezing here lately). While it wamed I opened the engine bay and for some reason I took the oil cap off (I was checking for that horrible yellow sludge). As I did this the engine started to cough and splutter I so quickly put the cap back on and everything stabalised. It occured to me that the cap and the oil fill tube must somehow effect compression and that if a tiny bit of air was getting sucked in it could have effect on performance. So just for kicks I put a piece of thick cling film over the oil fill tube and placed the cap back on. Whoa! What an amazing difference. Seems my 996 just found a good few extra pony's. My cap is the new green type. Only got it last year. But me thinks these things still let air in. Any comments?

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By taking the oil filler cap off you will have introduced an air leak and the ECU will richen the mixture accordingly, hence the rough running. Small leaks, like a leaking cap, can cause the idle speed to raise 3-400 rpm, and again it adversly affects the mixture control. If you have a scanner, plug it in and check the idle speed (should be 680 rpm), and also see if you have error codes.


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Taking the cap off will eventually cause a CEL. The crankcase ventilation is part of the emissions control.

Check the inside of the cap for a black o-ring if it's not there that would explain the leak - but also usually causes a CEL. Better make sure it didn't fall out when you took the cap off too.

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Checked the cap and the O-ring is there....thank the Lord.

It's weird, the cap seem to fit perfectly and the car drives perfectly normal (especially with the new gearbox ;) ) but it seems to have more punch with the cling film on. Weird!

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