Running well BUT....Idles at 2000rpm sometimes!

[Robm3]

Not sure if anyone's encountered this before but my LT5 has started idling rather highly at odd times.

I start it cold, no worries idles a touch fast (naturally) then settles down to a steady 1000rpm. If I go for a fast drive, sometimes it's okay, other times it'll keep reving at 1800-2000rpm and just surges up and down. Doesn't happen all the time though and when it is happening, if I pull up to a complete stop it calms itself down after about 30-60 seconds.

I replaced the Idle Valve control unit (little black thing hanging off the side of the air intake chamber) a few weeks back, perhaps it's something to do with the ECU calibrating the new sensor??

Any ideas??

[Paul Workman]

It has the ear marks of a "vacuum" (air) leak. In my case it was the intake and IH that needed to be re-torqued. Some of the bolts were barley finger tight. Also, on my 90 there was a vacuum line running to the TB on the underside. It discovered that it was left disconnected when I bought it. That caused me some erratic idle once as well.

Others will chime in too.

P.