Weird idle condition

Well, as of late, my bus (series 60 DD) does something interesting. On it's own, it decides to jump to an idle of 1000 rpm!

So if I am backing in or out of its parking spot, and it decides to jump up to 1k rpm, it gets your full attention for sure!

If it does in in neutral, you can't shift as the tranny won't allow a shift at that high of an idle.

This happens instantly, like when you flip your high idle switch.. Also if it is idling at 1k and you hit the high idle switch, it goes up to 1100 like normal. Disengaging same puts it back at 1000.

My only thought so far is possibly the throttle position sensor..

Any thoughts ??

I should mention, it arbitrarily kicks in and out this 1K idle condition on its own at random intervals..

I had the same problem on my bus. Fixed the problem by changing out relay in drivers compartment. The relay is marked as high idle. There is also second relay in same area that should be checked. This is marked as ddec. Once changed the relay have not had problem again. Hopes this helps.

Thanks Kim, did yours also idle around 1k, and go still go up to 1100 when you engaged high idle ??

Sorry of the delay in response, but in airports today. Yes, that was the exact symptom.