Engine not correctly returning to idle

[jwrayth]

So after a week of running smooth I seem to have developed more problems! My engine starts properly from cold and settles on an idle of about 775 RPM with a very minute bit of hunting to start off. However, after some time running the idle begins to stick around 1500 rpm to 2000 rpm. If I manually depress the idle microswitch then my revs _sometimes_ drop back to the expected 775 RPM, however sometimes engaging the microswitch appears to do nothing.

It appears to only get worse the warmer the engine gets, to the point where engaging the microswitch does nothing to help the engine idle.

I assume I'll need to take the air filter assembly off to get a better look, but can anyone advise as to what the issue may be? Bad micro-switch or a bad grounding would be my inclination, but I'm not sure if there is something else obvious that I am unaware of...

[Jonathan]

A couple possibilities...

When you depress the idle microswitch, are you getting right in there with your finger and pushing it down? Or are you turning the throttle spool which in turn moves the linkage underneath and pivots the lever arm which pushes on the microswitch?

If you know for certain the microswitch is being pushed and nothing is happening, then yes, it may be a bad switch or connection or the like.

If the microswitch does work when it is for certain pushed in, then it could be that things are not adjusted correctly or lubricated well enough for it to spring back to it's default position, thus pushing the microswitch.

There are a number of ways to correct that latter situation... easy one is to adjust the set screws on the lever arm so that at rest it pushes in the metal tab of the microswitch. Or if there is too much slack in the linkage underneath, it can be dialed in to change the length accordingly. Your throttle spool spring may also not be in it's notch properly or just flat out weak or rusty and crusty and not moving freely. Same goes for the spring on the lever arm itself. Or take the butterfly valves section off and clean it up good and lube it up good. Or the throttle cable is too short or a handful of other less likely problems...

If the microswitch does nothing, it could be a bad switch, but it could be something else too. Confirm the vacuum advance solenoid back there is ok. The vacuum connections should follow the drawings and the electrical connector needs to be clean and snug.

This is a common issue on the cars it seems and luckily it has some pretty straight forward solutions 'most' of the time :)

Since you said it gets worse when the car warms up, my vote would be you need to clean the butterfly valves pivot assembly and lube it up. My experience (with my car anyway) says there is more resistance to this pivoting freely once the car is warmed up and full vacuum on it, etc. Which could explain why you see it more often when the car is warm.

[jwrayth]

With the engine not running I can manually move the throttle spool and hear a definite click on the micro-switch. With the engine running I've taken a micro-driver and used that to physically depress the idle switch which initially works, but as the engine warms up it becomes more and more unreliable. It doesn't seem to be consistent though, as sometimes depressing the switch works first time when warm and other times I've had to press it multiple times to get the idle to return...

[Elvis]

I've posted a solution that worked on 3 cars I had here and that
had the exact same problem.

I posted even pics. SEARCH will help.

A little tip - when idle is too high - does pushing the butterfly lever
help ? (not only the switch)

[jwrayth]

I did use the search function and found a number of threads with differing symptoms where your response is suggesting to use the search function. So rather than just linking to your solution (or as suggested in a few places, someone knowledgeable of such things putting a sticky thread / cheat-sheet on debugging high engine idle) I now mostly get results of you being frustrated about people not using search rather than useful results.

I'm not wanting to nitpick you as I was more than able to tell from your previous responses you've got some serious ire for anyone experiencing idling issues, but I have read your replies with more detail than you've given to me and in some cases you suggest it's the Idle Speed Motor or ECU, and in others that it's bad springs for the butterfly plates and none of those situations match my exiting diagnosis/symptoms and I wanted to get a second opinion before I start tearing apart my car.

In the future I'll just blindly follow the first suggestion I find on the internet without verifying with more experienced members of the community; I'm sure that's the best and safest way to look after my DeLorean.

[Bitsyncmaster]

It sounds to me like your throttle is sticking and not closing fully. Take the throttle spool off and put grease on the spring. That was a fix for my sticking throttle. Your throttle will close easily when the engine is not running. Whit the engine running the vacuum makes the throttle sticky. Also move your spring to the higher setting if not already there.

[Elvis]

I took my time and posted tips and pictures of things that work reliable.
Searching the forum is time you can invest now - and it looks like you did it.

Did you push the butterflies closed instead of just pushing the switch ?
For this simple test nothing needs to be taken apart.

VACUUM from the engine and worn bushing/bearing prevented the butterflies
from closing completely when the engine is running.
Especially when releasing the pedale slowly and when the engine is hot.

Is it a problem like this ? well, then it's the spring problem.

Maybe you believe Dave more than me ?


And yes I find it frustrating that eveybody thinks he has a new idle problem
instead of following the known stuff first. It's about one per week.
I even found and talked to people who do not like to search and who want their
personal reply. Why ? Because it saves them time ?

There's another guy I was talking to lately who thinks his tacho is bad because
at idle it shows up to 1200rpm :hysterical: :lol:







I did use the search function and found a number of threads with differing symptoms where your response is suggesting to use the search function. So rather than just linking to your solution (or as suggested in a few places, someone knowledgeable of such things putting a sticky thread / cheat-sheet on debugging high engine idle) I now mostly get results of you being frustrated about people not using search rather than useful results.

I'm not wanting to nitpick you as I was more than able to tell from your previous responses you've got some serious ire for anyone experiencing idling issues, but I have read your replies with more detail than you've given to me and in some cases you suggest it's the Idle Speed Motor or ECU, and in others that it's bad springs for the butterfly plates and none of those situations match my exiting diagnosis/symptoms and I wanted to get a second opinion before I start tearing apart my car.

In the future I'll just blindly follow the first suggestion I find on the internet without verifying with more experienced members of the community; I'm sure that's the best and safest way to look after my DeLorean.