High idle when parked but not when driving

[CarterH]

I recently had the rear subframes replace and it's had a high idle (sitting at 1100 - 1600rpm) since then. It's worth noting it's also been driven on pretty hot days but I drove it on a cold morning and it idled at a nice 800rpm. But as soon as I got it back home though, it was straight back to 1100rpm and I gave it a rev and it went to 1600 but then only came back down to 1500 and stayed till I shut it off. Anyone had experience with this? My own looking online has said it's throttle or vacuum leak related but a mechanic I called said it might be electric or related to fuel injectors.

It's an M30 engine since that will help. I've also got a video and pictures if that helps more.

[demetk]

My guesses. 1. TPS not giving an idle signal or 2. stuck ICV not closing properly.

[moroza]

Hot in January? Oh, duh, southern hemisphere.

It's not the injectors. It might be electronic. It's probably not an intake leak, as those tend to lower idle, not raise it. So let's see... you're driving along and put it in neutral, idles at 800? Come to a stop and it's over 1000? What happens if you bring it to a stop in neutral? Or blip the throttle in neutral while moving? My hunch is throttle cable/linkage.

[CarterH]

Hot in January? Oh, duh, southern hemisphere.

It's not the injectors. It might be electronic. It's probably not an intake leak, as those tend to lower idle, not raise it. So let's see... you're driving along and put it in neutral, idles at 800? Come to a stop and it's over 1000? What happens if you bring it to a stop in neutral? Or blip the throttle in neutral while moving? My hunch is throttle cable/linkage.

Yep, it's been pretty toasty in this part of the world lately but not as bad as last year.

Not exactly. In park/neutral it would usually sit somewhere around 600-800 but with this issue it became between 1100-1600, but when put into drive it would then fall back down to 800 or so. Sitting at traffic lights or anything else was fine but the moment I put it into neutral or park, the revs would shoot up almost immediately.

It's sorted now hopefully. It seems the throttle linkage was jamming a little but a little lubrication seems to have fixed it, I'll have to wait and see. I did a vacuum check and that came up fine so if the lubrication hasn't fixed it, then I'll move on to checking if the TPS is having problems or if the ICV is dirty (a dirty ICV caused issues in my E36 so I wouldn't be surprised). I appreciate all the input though guys. I'm glad that so far a nice cheap and simple method fixed it instead of me jumping to more difficult/expensive fixes.