Got A Strange Idle, Lower Than 600 Rpm

[NZ R34]

Hi guys.

When I start my car, it idles at about 600 rpm, and gives a bit of a shake to a car. When i switch off overdrive, it resumes back to normal for some time, but starts to drop after about 5 mins

Anyone can advice, what would be the reason for this to happen?

Bought this car just today, so dont know much about it.

It is a R34 GT,1998

Thanks

[petern]

how is your fuel economy?

if its bad then i would look at changing the spark plugs.

Same low idle happened to my car recently - usually morning cold starts starts high and stay there until the motor warms up.

Had shocking fuel economy too.

Changed the 3500ish km cooper plugs back to the platinum (had only 10k kms on them) and it revs high and back to normal again