VT V6 has a strange idle while coasting..?

[CV6Z]

my VT V6 auto sedan has a strange idle while im coasting downhill on the highway or in general...seems to only occur at highway speeds ( 80km/h onwards). say im cruisen along the highway and i ease off the throttle, the rev's drop to 1100rpm and "rev" up to 1600rpm (roughly) and just keeps dropping and rising as though im actually revving the engine...? its annoying and im sure its not supposed to happen!! any thoughts on this?

[acarmody]

Mine does too, come off highway, let go of accelerator, and revs 'bounce'. Quite annoying but for life of me can't find why.

[CV6Z]

Mine does too, come off highway, let go of accelerator, and revs 'bounce'. Quite annoying but for life of me can't find why.

exactly!! lol i have no idea why, but it does get annoying...just seems to bounce up and down?

[vtbaby]

does it do it while your sitting still at the traffic lights?? cos i swear my foot is on the brake then sometimes my car has a little jolt/bounce whatever lol and i panic a little cos i think omg 1 more time and i will run up the ass of this car in front.

[CV6Z]

havnt noticed it while stationary but i'll go for a cruise today just to see if it does...

[acarmody]

Mine never does it at idle, just when decelerating.

[TrikkBen]

Yer my car did that aswell, sounds like the converter is locking and unlocking.....

[showbags]

pipe between EGR valve and inlet plenum is leaking.

[acarmody]

I try some gasket sealant around the pipe and see if that makes any difference.

[CV6Z]

pipe between EGR valve and inlet plenum is leaking.

yep only happens when decelerating....how do we fix this problem and where is this EGR valve located? cheers

[acarmody]

Well some sealant around the pipe would fix this if it was the problem. EGR valve is the pipe that goes from the passenger side exhaust to the area behind the throttle body, is just a pipe with a big cylinder shaped valve in middle.

[brad_m_is]

Its normal every commodore does it!

[showbags]

it's only normal because nearly every commodore i've seen has a cracked egr pipe. they're mad from flexible stainless steel and they crack on the exhaust end due to thermal stress. undo the two bolts & remove the pipe. you will find it's cracked just below the pressed olive in the pipe. seal it up( i've found CRC maniseal is the most successful) and put it back together- and hey presto no more annoying surge when you bake off down hill.