Mk3 Fast Idle

[Ninety-Eight]

I have a 1995 Mk3 LS400. The idle speed when warmed up is eratic. Sometimes correct and sometimes it is like 1200+ RPM. It can be anywhere in between as well.

I am assuming it is one of the following:

1. Idle control valve faulty or sticking

2. TPS faulty or sticking

3. Some form of vacuum leak.

Is there anything which is a "known issue" on this engine?

Any hints or tips welcomed.

[steve2006]

I have a 1995 Mk3 LS400. The idle speed when warmed up is eratic. Sometimes correct and sometimes it is like 1200+ RPM. It can be anywhere in between as well.

I am assuming it is one of the following:

1. Idle control valve faulty or sticking

2. TPS faulty or sticking

3. Some form of vacuum leak.

Is there anything which is a "known issue" on this engine?

Any hints or tips welcomed.

I would clean # 1 and the throttle body/butterfly after checking as you suggest for a vacuum leak on the inlet manifold area, another poss is the coolant temp sensor/wiring.