Why does car rev high when starting it in the morning?

Maintenance/Repairs
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1

I have a 2003 Toyota Corolla with 90000 miles, that gets regular maintenance.

I’ve tried taking it to the dealership, but all they want to do is blindly follow their flowchart, making me spend lots of money in the process. Per their instruction, I’ve already replaced the battery, I’ve done a tune up, including spark plug replacement.

I think it’s probably some sensor that is busted. The car has 90000 miles now (I bought it 3 years ago with 59000), and it didn’t have this problem before. In the past, it wouldn’t rev high. But now, the revs wont go back to normal unless you spend a good 10-15 minutes in park until it “warms up”, even though this also occurs in the summer.

Generally though the car has run great. It just revs high when starting up in the morning.

Can anyone identify some of the main causes of this symptom. Coincidentally, every used car I’ve ever owned eventually gets this problem.

2

Try another shop. It could be as simple as a bad temp sensor telling the engine that it’s colder than it really is.

By the way, what is the ambient temperature typically when it does this?

3

I think I’ve noticed it in the summer and winter. Right now car is started in the 40s, but I’ve seen it happen in the 70-90s.

4

That could still be the temp sensor. The computer should be checked for codes as the first step, however a bad temp sensor may not cause a code to be stored. The ECU has no comparative reference to know that the engine isn’t as cold as the sensor says it is. IUt just takes the sensor’s “word” for it.

5

There’s no check engine light on. So I think you are right that any temp sensor malfunction would go reported by the computer. This would explain why all my used eventually get like this, and maybe the mechanics are not smart enough to figure it out without OBD codes

6

A scanner capable of monitoring live data can be bought for less than $100. A previous thread here mentioned an OBD linking program for a lap top with detailed diagnostic procedures. Maybe you can become more knowledgeable of the cars system than the dealership mechanics. Certainly, if the data link indicates that the engine temperature is 60 after 30 minutes of driving the process for repairing would be considerably streamlined. But I am unsure just what the dealer has done to find the cause for your concern. Have you actually given them the opportunity to run their diagnostic tree? And after running a complete diagnostic for the high idle all they recommended was a new battery and a tune up? Something doesn’t add up.

7

Excellnt idea Rod, as usual. I was thinkin’ a lab thermometer, a lab vessel, a multimeter, a hotplate, and a beer, but I like your idea.

8

How high is high? What’s the tachometer reading?

9

The engine will normally take much longer to warm up idling in park vs driving gently.
That said, I think it could be the beginnings of a sticky thermostat.
A fully bad thermostat will trigger the engine light, but this one isn’t that bad yet.
On a daily driven car I recommend changing the thermostat every 5 years or so anyway,
so it’s due.

10

Codes can exist whether the CEL is on or not. If there are no codes present then I would connect a vacuum gauge and rule out any vacuum leaks while making sure things appear normal mechanically.
This is cheap and easy to do.

After that, you might consider the possibility of an Idle Air Control valve acting up, sticky throttle plate, etc. This is where an induction cleaning could possibly help.
It might also be added that sometimes faults can exist without any codes being set and this is especially true with Idle Air valves, EGR systems, etc.

I also agree with circuitsmith about the thermostat scenario and changing them ever so often. Many an engine has been roasted due to such an inexpensive and overlooked part when the T-stat failed in a closed position.