I'm working on my daughters Accord. Although I'm working on an oil leak, I noticed it wouldn't accelerate at idle when cold. I found a broken water temp sensor, and replaced it. Now, it works fine when it's cold, but it idles around 2-300 when it warms up. I tried the computer reset procedure, and it ldles good, until you hit the accelerator pedal, then, from then on, it idles low again. I've cleaned the IACV and throttle body, and tried the reset and relearn with the same problem. It's not had a idle problem when warm before. I fixed one problem, and caused another. Should I go ahead and try to reset the idle speed with the idle air control disconnected? I don't understand why it won't "relearn". I also don't want to go "turning screws" when I shouldn't.

 

When you look at the tachometer, the first mark past zero is 500 (not 250 rpm). The next mark is 750.

So what rpm is the car idling at?

 

It's idling at almost zero. It runs so smooth, I've never seen a car idle that low. I'm just guessing since it's so low. It is below the first mark.

 

Have you undone any vacuum lines? I've had this problem after cleaning IM. It ended up being the 2 vacuum lines for the EGR Control Solenoid. There is one that runs into the IM, and one runs to the EGR lift valve. I had them backwards. Switched them, and it fixed my idle issue.

 

The only thing I did was to replace the temp sensor. Didn't have anything loose.

 

I would guess that the car would stall out or run poorly if it was idling that low.

Maybe the idle is normal (750 rpm), but the tachometer signal is not correct.

The tachometer signal comes from the distributor, so check that the electrical connectors are secure and there is no oil/dirt in them.

Check any electrical connectors near where you did the work (was it the sensor under the distributor that you replaced?).


There are some digital timing lights that will read rpm. The auto parts stores may have them as a loaner tool. You may want to call and see.

 

Suggest disconnecting Idle Air Control Valve (IACV) and see if idle goes even lower. It should idle about 550 +/- 50 rpms w/ IACV disconnected. Idle speed is adjusted w/ air bleed screw near TDC on throttle body inlet.

Note, IACV should be cleaned before attempting to adjust idle speed if you determine the tach is working correctly.

Tach speed can be checked against car speed in top gear & overdrive. 2550 rpm should be ~65 mph. 2200 rpm about 55 mph.

good luck

 

Believe me, the car is idling that low. You can almost read the writing on the belts. I know the difference between a faulty indicator, and an engine that idles low. I don't need the tach to tell it's idling low. The engine runs great and it's not a tach problem, but thanks for all your help.

 

Just for everyone's info, even though replacing the water temp sensor shouldn't have an effect, it must have. Cleaning the throttle body, and idle air motor, and resetting the computer didn't help. Bottom line was the idle actually changed while the temp sensor was faulty. For some reason the computer wouldn't relearn the idle. I wound up having to manually reset the idle. I had to dig out the putty, so I don't think it'd ever been changed. Anyway, works good now. Hopefully, it won't change down the road. Thanks for the ideas.

 

I am glad you figured it out and thank you for posting your solution.