Highlander Engine Races on Start-Up

[Hokie76]

Yesterday, the engine in my 2003 Highlander 4-cyl./55K miles started racing on cold start-ups. Tapping the accelerator briefly brings down the speed, but it goes right back up to about 1,500 RPM. The idle remains high when coming to a stop, requiring a lot of pressure on the brake. Sometimes it stumbles, but does not stall, as the transmission downshifts. It runs rough after stops, especially with the A/C on. The "check engine" light has not come on. The condition seems to improve somewhat after the engine warms up, but happens again when started after sitting for several hours. Does this sound like a MAF sensor, dirty throttle body, vaccuum or fuel injector/pump issue? Thanks.

[oldnslo]

My first guess is to look for vacuum leaks first. A vacuum leak will cause an engine to run at higher RPM's. This leak would have to be down stream of the MAF. Might also explain rough shift since computer may not know thr true engine RPM. (Not sure how the computer monitors engine RPM.) Have done any recent work on this engine? If so look at all of the hoses in the area you were working. Some of these hoses are easy to dislodge or break without even reallizing you damged them. (Don't ask me how I know this) :-(

I doubt that injectors or fuel pump would cause this since a typical injector failure is they either start harder or miss.

With all of the sensors on cars it is also possible that the TPS (Thottle Position Sensor) may be sticking or starting to fail. Not to common but possible.

Also possible corroded conection on a sensor but would not expect this to change sinificantly with temperature.

Good luck, as we all know random failures are a real pain in the ass.

I had all of the above problems on my old Beemer and symptoms were similar to what you are describing.

Roy

[Hokie76]

Thanks, Roy. I visually checked all of the lines/hoses I could see, but nothing appeared loose. The last work was done by the dealer a couple of months ago when the replaced the battery and drive belt.

It raced again this morning on start-up, but wasn't idling as fast as yesterday. I'll probably take it to the dealer Friday and let them check it out. I'll report back with the result. Thanks.

My first guess is to look for vacuum leaks first. A vacuum leak will cause an engine to run at higher RPM's. This leak would have to be down stream of the MAF. Might also explain rough shift since computer may not know thr true engine RPM. (Not sure how the computer monitors engine RPM.) Have done any recent work on this engine? If so look at all of the hoses in the area you were working. Some of these hoses are easy to dislodge or break without even reallizing you damged them. (Don't ask me how I know this) :-(

I doubt that injectors or fuel pump would cause this since a typical injector failure is they either start harder or miss.

With all of the sensors on cars it is also possible that the TPS (Thottle Position Sensor) may be sticking or starting to fail. Not to common but possible.

Also possible corroded conection on a sensor but would not expect this to change sinificantly with temperature.

Good luck, as we all know random failures are a real pain in the ass.

I had all of the above problems on my old Beemer and symptoms were similar to what you are describing.

Roy

[dupcharl6]

I have a 2003 Highlander and am having the same problems. Can you please tell me what the dealer told you? Thanks.

[Steve]

This might be common thing. When the engine races turn off the aircon system totally (not heating, fan.. anything swith to OFF).. if it lowers then this is a feature that helps warm the engine faster. This is a feature with some Toyota diesels such as the Lexus IS220d

[dupcharl6]

This might be common thing. When the engine races turn off the aircon system totally (not heating, fan.. anything swith to OFF).. if it lowers then this is a feature that helps warm the engine faster. This is a feature with some Toyota diesels such as the Lexus IS220d

I tried that and it didn't help unfortunately. I've had the vehicle for two and a half years and it only started doing this a few months ago. It's doing the exact same thing as Hokie76's Highlander. In addition, mine will sometimes (albeit rarely) oscillate between 1000 and 1500 RPM on start-up. Any help would be appreciated.

[B-R-T]

Check for vacuum leaks (hissing sound when engine is running).

Idle air control valve could be failing.

EVAP purge valve could be failing.

MAF, fuel system is not likely. It cannot increase engine speed without more air coming in.