Revving high at idle

[Nina]

Stuck!

I'm stumped! The coolant light on my 2008 Yaris LE Auto with over 200k was taking way too long after warming up for the light to go off on the dashboard to the point that the car could not go into overdrive on the highway because it's supposed to reach 55*C. Eventually, the light wasn't shutting off at all! So I changed the thermostat twice and tried three different engine coolant temperature sensors and replaced the coolant with fresh mixture. I hooked up my Torque OBD app and noticed it doesn't go higher than 40* C when warming up.

Now the car also revs at about 2000 rpm's in park but does come down to the normal 750 rpm zone but only when in drive and reverse but as soon as I put it in Park or Neutral, it revs high again. I cleaned the TB and replaced the MAF sensor and checked all hoses for a vacuum leak - nada. No change!!!

I though I'd spend on the small parts first but they are also adding up! I'm at a loss here...I cleared the ECM many times by unplugging the battery as that would have forced the car to re-learn its rpm's and taking it for a spin but the two problems continue.

Is the ECM toast? Everything else works like it should...

[sh0rtlife]

if the scan is showing it staying cold, then you still have a coolant issue, PERIOD

now just because you changed out the t-stat doesnt mean you got a good one, in fact bad out of box is not uncommon, what you need to do is take the 2 you have out, drop them in a pot of water with a MEAT thermometer and stand there and watch the temps and the t-stats and see when they are opening, if its before anything before say 70c they are junk...if memory serves the "normal" for most engines is somewhere between 80-90c, but i dont know of any that are below 70c or higher than 98c(180-210f)

next up verify your fan isnt running..if its running BEFORE you reach those temps then its atleast part of your issue and you need to change out the fan temp switch most likely tho it could be other things..if you have AC turn it OFF...AC forces the cooling fan on even before the engines warmed up

your temp sensor could still be bad as well right out of the box...never assume "new" parts are good....even if your buying top shelf parts....but if your buying cheep parts expect a 75% chance of bad out of the box or dead in less than a month

last thing that comes to mind is air in the system can cause all sorts of issues including never reaching temp...i assume you know how to burp the system?

DO NOT worry about the RPM issue untill the temp issue is solved..high idle is part of the "im too cold help me warm up" program and WILL NOT self adjust till normal operating temp is reached

[NYC-SE]

While your at it you might want to take that meat thermometer and stick it in the radiator and see what the actual temperature of the coolant is and if it corresponds to what your OBD scanner is saying. Always possible it is getting a false signal somehow.

[ex-x-fire]

Do a continuity check between the car's computer and the coolant temp sensor wiring. I bet you have a broken wire or bad connection.

[Nina]

Thanks for the "next steps" and suggestions people :)

Measurement Readings are as follows (I tested it with two different gauges - results slightly different between the two):

Coolant "burped" as needed.

Resistance of coolant sensor is around 2 ohms cold.

Resistance of the coolant sensor wiring is around 3.75 ohms.

Updating...

Coolant temperature idling at 61*C after 10 minutes...rpm's around 1,000

And after a drive with 33*C intake coolant is now 81* C !!!!!!!!

Success! Besides the two days and countless hours spent to achieve this, I'm glad this little engine "could" run right once again. I don't know why it wouldn't kick properly beforehand, but I'm happy now.

Nina