1998 4.1 Intermittent High Idle Speed- Cured

July 13, 2012

Just in case any owners of UK Rav4 4.1 (first) model have the same problem with idle speed as mine did- there could be many causes for this- vacuum leaks for eg., but this engine temp. sensor is only a tenner and so is a cheap place to start :-)

Symptoms are that idle speed is normal when engine is cold and warming up, but any warmer than that and the idle speed intermittently rises to about 2000 rpm, then falls back to the normal level again. It can do this with throttle closed or whilst tootling along at lowish speeds- here the fault shows as surges in power at small throttle opening, and lack of engine braking going downhill with throttle shut. Makes driving in heavy traffic a pain. I changed the PCV valve on the rocker cover which didn't cure the fault, then the engine temp. sensor which did. Engine temp. sensor is the right hand one of two temp sensors mounted on the coolant pipe on the right of the block- the left hand sensor is the one which drives the dash gauge. Note that my Haynes manual shows these two the wrong way around in their photos- though the text all seems correct for each one. The engine temp sensor has a connnector with two pins, the gauge sensor only has one pin and has a ground return. I stuck the faulty sensor in a pan and brought it to the boil with a meter connected- the readings were fine until near boiling, then they went mad as if the temperature was about -600C, then, weirdly, at boiling point it read ok again. Also, this is NOT bad enough for the ecu to give out a check engine light or record a fault code- I tried disconnecting the new sensor and started the engine- this immediately gave a temp sensor fault code and cel, but the idle seemed fine- so the ecu can spot a truly open circuit sensor ok.

This info relates to a 1998 UK model- US 4.1 models, and UK 4.2 and later, have OBDII and more comprehensive diagnostic codes than ours do it seems, which might have caught this temp. sensor fault.

Feel free to argue with any of this if you know more .... I'm strictly amateur here, just passing on what I have.

Dave

June 17, 2015

Hi Dave , I just read your post and I'm in the same situ I think, where did u source your Engine Temp Sensor, was it a toyota original and how much was it. I have been driven mad by hunting/stalling at low revs and have replaced the IAC (it was within resistance limits) with a used one (no change) then checked visually all pipes possible then clean out throttle carefully (it looked very smart) , it then purred on idle and drove perfectly for one our last night but then finally stalled after one hour this morning! A local nice garage had fitted the IAC and had a code reader for this car but showed no errors on anything at all . Im at my wits end and am due to have Toyota look at it next week which is what I have tried to avoid as they will just charge a fortune for anything.

I've ordered the temp sensor

Intermotor 55123 Coolant Temperature Sensor and a coolant temp sensor Fuel Parts WS1035 Temperature Sensor (the reservoir was empty) , and could an air temp sensor Intermotor 55728 Air Temperature Sensor, (not got yet) be at fault but not show a code?

Any advice warmly appreciated! Thanks Graham