RX300 2000 AWD

I was out on the interstate a couple of weeks ago on a long road trip and I was using the cruise control. I had to slow down, so I just disengaged the cruise control (pulled towards me.) Once I got through the traffic and the road opened up again, I simply resumed the cruise control.

What was odd was the tachometer shot up to about 4000rpm, then dropped back down to 3000rpm (normal cruise) then shot up again. It just oscillated between the two rpms but the car really wasn't speeding up at all; it held steady at 70 mph.

I observed the odd behavior for a few secs, then turned the CC off, turned it back on and reset it. Never had any other troubles the rest of the trip nor on the return.

Has anyone seen this before or have an idea why it might have been "confused?" Should I be concerned?

Lastly, although independent of the above behavior, I have one CC driving observation (maybe it's obvious, I don't know)

I. Don't resume CC unless your:
a) going faster than the set CC speed
OR
b) going no less than 3-4 mph slower than the set CC speed

In case b) the CC will speed the car up rapidly to get back to the set CC point.
Although that's OK, I think it's just better to keep your foot on the accelerator a little bit longer and get the car back to the CC speed before resuming CC. Saves gas, less wear on the engine (no high rev.)

Thoughts?
-Sam

 

I too have noticed relatively high RPMs if resuming speed from more than a few mph, but I feel this is normal. I've never seen oscillating RPMs as you reported, but I have had a few failures to restore speed where CC justs seems to not work. Whenever CC doesn't seem to work correctly I turn it off, then it is ok.