Hi Scotty and community, I'm working on the Aunts 2004 Toyota…


Hi Scotty and community, I'm working on the Aunts 2004 Toyota Highlander 2.4L DOHC that has a weird idling problem. 246,000KM

The problem has been known for the last two years.

Symptoms are, hot engine, idle drops under load from 900 rpms to 600 rpms and everything shakes when in any gear and/or with heater fan and/or exhaust fan low or high. Same symptoms if all three are happening or only one. I haven't checked if the head lights will cause this.

Cold engine would just increase the idle to 1,100 rpms

Things I have done with no improvement. I mean nothing helped.

Ultra sonic cleaned fuel injectors (beautiful misting spray),

Changed spark plugs,

Cleaned throttle body,

Cleaned IAC (Idle Air Control),

Disconnected Alternator while engine is running.

Cleaned/Checked oil control valve (VVT),

Changed Oil & filter (dark brown/black),

Changed Air Filter,

Cleaned Mass Air Flow Sensor,

Cleaned battery, alternator +, both ground wires on the sides of the engine to frame.

Compression Test

Cylinder 1 - 175 PSI

Cylinder 2, 3, 4 - 180+

Leak Down Test

On the gauge reading LOW (green), Medium (Yellow), high (Red)

Cylinder 1 - Bottom of the Low

Cylinder 2, 3 - Midway of the Low

Cylinder 4 - Upper Low

No past history for the vehicle beyond 2 years ago. And I can only assume nothing was done for the two years. I'm just glade it is not my vehicle even though I drive a Micra.

Other things i'm considering are

Lack of power (positive and negative wiring) going to the fuse box and/or ECU

Can't be engine timing.

Revisit IAC? Test ecu ability to send proper signal to the IAC? If the IAC is wide open, the engine can achieve 2,000 RPMS and if closed the engine stalls out.

Bad engine mounts? Can it cause the engine not to recover with a load?

Blown head gasket? No oil in coolant, No water in the oil. I can squeeze with force on the upper coolant line when the engine is hot.

OR.... Everything is running normal and fixing the engine mounts will fix the vibrations

For the good news, A/C started working that hasn't worked for the last two years.

The bad news is there's no engine codes to go by? So no check engine light. There was an EVAP problem but I fixed that.

Thanks in advance for your help and I do enjoy your shows Scotty. Cheers from Ottawa, Ontario, Canada

Comments (2)
No. 1-2

Thanks Scotty for you reply, I will do the propane test around the intake gaskets - all of them.

I just don't see that being the problem when the electrical fans kick in, that the engine struggles to balance out even though I disconnected the alternator to rule it out, not in gear.

My first gas car was in 2015 and I never worked on them, the rest of them were diesels. For all I know is that its normal for an engine in 2004 to do this. My moms car did this but hers had a carburetor and was old.

Scotty Kilmer
Scotty Kilmer


With that mileage engine is obviously Internally worn somewhat with those pressure readings. What do check for intake manifold gasket leaks they will often make them idle poorly