High idle cold start --sorry

[glockworks21]

I know this question has probably been asked a million times and Im hoping for a best guess starting point. It seems like there are a lot of things that cause can cause this. I get a high idle when cold, almost 2k rpm. it does it 90%of the time when i start it which is what is throwing me off. sometimes it wont do it at all. sometimes i can throw a rev or 2 into in after 30 second or so and it will drop to normal. it seems to idle fine after that and for the rest of the time i drive it. Trying to do everything myself on this and learning as i go. Can someone give me a "most common" starting point? If that exists? :o)



Thanks for your time

Dave

[Parzival]

Try this, Start the car and during the high idle, before giving it a few revs to bring it down. Go to the back and press on the throttle arm (where the adjustment screws are for the idle microswitch.) The thinking here is that many cars have tired or worn springs in the throttle body and on that arm. If yours is not returning to the closed position when cold then the butter fly valves will be slightly open and it may cause this condition. If when you press the arm down your idle returns to normal then this is likely you issue, and I can walk you through some ways to adjust it.
This is the easiest thing to check first, do this and report back what you find. If it has no effect we will have a few more things to check.

[Michael]

You are right. A lot of things can cause this. A bit of history on the car might help(has it sat for a period of time and you are waking it up? Does it get driven often and this problem just appeared?)

I would start with the basics. Make sure your throttle cable and spool are free and not sticking. Make sure your idle circuit is working and engaging at closed throttle. Vacuum leaks are always a possibility. Other possible causes are idle air valve or maybe even the CPR but that usually causes a dying problem rather than a high idle.

My first inclination is the idle circuit is not working either because the plate is not engaging microswitch or the switch itself is faulty.

[82DMC12]

Did you see my ongoing thread? I am going through this similar issue and narrowing down the possibilities as I continue to work on it. Maybe you can learn something from it.

https://dmctalk.org/showthread.php?19214-High-idle-speed-and-no-more-surging-after-intake-rebuild

[glockworks21]

You are right. A lot of things can cause this. A bit of history on the car might help(has it sat for a period of time and you are waking it up? Does it get driven often and this problem just appeared?)

I would start with the basics. Make sure your throttle cable and spool are free and not sticking. Make sure your idle circuit is working and engaging at closed throttle. Vacuum leaks are always a possibility. Other possible causes are idle air valve or maybe even the CPR but that usually causes a dying problem rather than a high idle.

My first inclination is the idle circuit is not working either because the plate is not engaging microswitch or the switch itself is faulty.


Ive revved the engine from the spool when it is at high idle. I have also engaged that switch and it does not seem to do anything to the idle. Maybe replace it first?

[glockworks21]

You are right. A lot of things can cause this. A bit of history on the car might help(has it sat for a period of time and you are waking it up? Does it get driven often and this problem just appeared?)

I would start with the basics. Make sure your throttle cable and spool are free and not sticking. Make sure your idle circuit is working and engaging at closed throttle. Vacuum leaks are always a possibility. Other possible causes are idle air valve or maybe even the CPR but that usually causes a dying problem rather than a high idle.

My first inclination is the idle circuit is not working either because the plate is not engaging microswitch or the switch itself is faulty.


there are 30k plus of receipts done over the last 15 years or so but then it sat for a long time. Ive put about a thousand miles on it since getting it mostly driving around town. I am still trying to go through everything. I have changed the vacuum lines that are visible. i havent done the ones under the intake. Its always started right up and runs well. I drive it at least once a week but the problem has been there from the beginning. it did however go from 1500 to 1800 rpm high idle to about 2k. so it seems its gotten worse.. i started it this morning cold and it idled normally for about a minute then it jumped.. then about a minute or so later it dropped...

[82DMC12]

Ive revved the engine from the spool when it is at high idle. I have also engaged that switch and it does not seem to do anything to the idle. Maybe replace it first?

Disconnect the wires from the back of the microswitch and make sure the switch is actually working with a multimeter set to ohms. See that the switch closes the circuit when you press the switch in. And goes open circuit when the switch is in rest position.

You can also set your meter to DC volts, put the red probe on the battery + terminal (or jump start terminal in the engine compartment) and the other wire on black/green at the idle ECU (black box behind the driver seat, and the black/green wire is on the inner of the two white plugs). It should show 12V when the switch is "on" or in, and 0 volts when the switch is off. This way you know the wiring for the switch up to the Idle ECU is correct. The idle microswitch provides the ground for the ECU and tells it when you are idling.

[Michael]

Yeah definitely just test the microswitch.
.no need to just start throwing parts on it and hope you fix the problem.

You may want to crack the idle computer case (unless it's new) and look at the board. When my idle computer went bad, I was easily able to see a burnt path. That's not to say a bad one will have a visible clue. The only real way to test one is swap it with a known good one but you might "get lucky".

[glockworks21]

Disconnect the wires from the back of the microswitch and make sure the switch is actually working with a multimeter set to ohms. See that the switch closes the circuit when you press the switch in. And goes open circuit when the switch is in rest position.

You can also set your meter to DC volts, put the red probe on the battery + terminal (or jump start terminal in the engine compartment) and the other wire on black/green at the idle ECU (black box behind the driver seat, and the black/green wire is on the inner of the two white plugs). It should show 12V when the switch is "on" or in, and 0 volts when the switch is off. This way you know the wiring for the switch up to the Idle ECU is correct. The idle microswitch provides the ground for the ECU and tells it when you are idling.

I just ordered a new multimeter. I lost or loaned one out long time ago. Never needed it for any car ive had recently. Its seems like its a must have for a DMC though. :o)

[82DMC12]

I just ordered a new multimeter. I lost or loaned one out long time ago. Never needed it for any car ive had recently. Its seems like its a must have for a DMC though. :o)

The specialty shop tools I use the most on my DeLorean:


multimeter
Actron Dwell and RPM meter
K-Jetronic fuel pressure test gauge with control pressure valve
Air compressor
Camera on a wire (Harbor Freight $85)
Cooling system pressure tester (NAPA)

[glockworks21]

sharing a few pics. Ive cleaned up a lot in the engine bay. I know there are still things not right. I dont know the quality of work that was done over the years but there were a lot of things routed wrong. I still think there are. If anyone sees anything obvious please share. fuel lines are my next step. Thanks for all your guys help. All new to me.

[glockworks21]

Yeah definitely just test the microswitch.
.no need to just start throwing parts on it and hope you fix the problem.

You may want to crack the idle computer case (unless it's new) and look at the board. When my idle computer went bad, I was easily able to see a burnt path. That's not to say a bad one will have a visible clue. The only real way to test one is swap it with a known good one but you might "get lucky".


Ok thanks. I will look !

[82DMC12]

sharing a few pics. Ive cleaned up a lot in the engine bay. I know there are still things not right. I dont know the quality of work that was done over the years but there were a lot of things routed wrong. I still think there are. If anyone sees anything obvious please share. fuel lines are my next step. Thanks for all your guys help. All new to me.

Looks pretty nice overall. You really need to replace all of the fuel lines though, they are original-style and can spontaneous start to leak and start a fire. There are 13 fuel lines between the fuel filter and fuel return including all the injector hoses, cold start, frequency valve, and control pressure regulator. Then there are two flexible lines on the fuel accumulator that have to be replaced, and the two flexible lines on the fuel pump unless you've already updated to the modern GM-style fuel pump. Really can't recommend using the car without replacing all these lines at this point in that car's life. Too risky.

[glockworks21]

Looks pretty nice overall. You really need to replace all of the fuel lines though, they are original-style and can spontaneous start to leak and start a fire. There are 13 fuel lines between the fuel filter and fuel return including all the injector hoses, cold start, frequency valve, and control pressure regulator. Then there are two flexible lines on the fuel accumulator that have to be replaced, and the two flexible lines on the fuel pump unless you've already updated to the modern GM-style fuel pump. Really can't recommend using the car without replacing all these lines at this point in that car's life. Too risky.


started it and jumped to 2k rpm. I immediately pulled the connector off the idle speed regulator motor and it instantly dropped to 900 rpms and stayed there. When i plugged it back in it spiked for a minute and dropped back down. I believe its the original one. Do you think its bad ? or is it just a gremlin chase?

Thanks,

Dave

[Michael]

started it and jumped to 2k rpm. I immediately pulled the connector off the idle speed regulator motor and it instantly dropped to 900 rpms and stayed there. When i plugged it back in it spiked for a minute and dropped back down. I believe its the original one. Do you think its bad ? or is it just a gremlin chase?

Thanks,

Dave

I'm not 100% sure but I believe there is a way to test those on the car. Pull the ISM (leave it connected to the plug of course) and watch the valve opening when the ignition is turned on. I think it opens fully then closes? I will have to search it.

[Bitsyncmaster]

started it and jumped to 2k rpm. I immediately pulled the connector off the idle speed regulator motor and it instantly dropped to 900 rpms and stayed there. When i plugged it back in it spiked for a minute and dropped back down. I believe its the original one. Do you think its bad ? or is it just a gremlin chase?

Thanks,

Dave

There is no return spring in the idle motor so pulling the connector should not make it change. Maybe you have a marginal connection on the connector. Next test would be to move the wires (sideways, pull, push) when high idle to verify bad or good connections.

[Michael]

This thread may help. +1 on the connection. If you pulled the plug, the idle would probably reamain high or rise, not fall.

https://dmctalk.org/showthread.php?11871-idle-air-control-test-procedure

[glockworks21]

There is no return spring in the idle motor so pulling the connector should not make it change. Maybe you have a marginal connection on the connector. Next test would be to move the wires (sideways, pull, push) when high idle to verify bad or good connections.


I tried that with no change. I took out the idle motor and cleaned/oiled it. i jumped it to test its working and it clicks open and closed. I removed the micro switch and its checked it with multimeter. it works as well. I disconnected the plug on the cpu behind drivers seat- one closest to center of car and the idle spiked up like the other tread said it would. when i disconnect the other clip on that computer it did nothing.

after all that it still jumped to about 2k this morning during cold start. and i can still disconnect the idle motor and it drops immediately.
idk
pretty sure this is original

[glockworks21]

ok.. so the valve isnt closing after 30 seconds or so. the motor hums and it closes about a 1/4 of the way. i put a screwdriver in there to see if i could move it and can feel it vibrating. Ive left it for a few minutes and it has yet to close. Im just going to order a new one unless someone has another idea.
Im guessing the motor is gradually burning out.
I really appreciate all everyones help.



Thanks again.
dave

[Rich]

Do you want to verify the idle speed motor is dead/dying and/or give it a couple of more cleanings? Verify the wiring is OK in any case. A new ISM won't fix that.

This ISM test is taken from another thread on the ISM (https://dmctalk.org/showthread.php?11871), which lists other handy elec tests for this device and the wiring:


Another way to test the idle air motor is to measure the resistance with your multimeter. A good motor should read +/-20 ohms resistance between any two pins that are next to each other and +/-40 ohms resistance between the two outside pins.

The idle air motor can be cleaned out if it is not too damaged. The most common way to do this is to detach the motor from the car and spray it out with carb cleaner. Fill the motor with carb cleaner and plug both openings in it. Shake it up and roll it back and forth in between your hands like you are making a ‘snake’ out of clay. You should hear it clicking back and forth. Repeat the cleaning process several times, drain the motor, and then allow it to dry for an hour or so.

[Bitsyncmaster]

ok.. so the valve isnt closing after 30 seconds or so. the motor hums and it closes about a 1/4 of the way. i put a screwdriver in there to see if i could move it and can feel it vibrating. Ive left it for a few minutes and it has yet to close. Im just going to order a new one unless someone has another idea.
Im guessing the motor is gradually burning out.
I really appreciate all everyones help.



Thanks again.
dave

Try shorting the thermistor wires and see if it closes. Thermistor has to be plugged into the ECU.

Don't use a screwdriver to turn the idle motor valve. It's a soft metal and you could damage it. I'm guessing someone already did damage it which would be why it's not closing more. Use something soft like wood.

Also note the idle motor will not close fully with a stock ECU. It will still be about .1" open.

[glockworks21]

the motor is reading around 10 ohms on the pins next to each other and around 20 on the outer pins.
?

Thanks
Dave

[Bitsyncmaster]

the motor is reading around 10 ohms on the pins next to each other and around 20 on the outer pins.
?

Thanks
Dave

That is typical of the OEM idle motor.

[glockworks21]

That is typical of the OEM idle motor.


found the wide open switch is not connected to anything(i think thats what it is) the other 2 open plugs on the left side are for something to do with an automatic right?
the deeper i go the more i find.
cold start this morning and idle jumps to 2100. same as before. I disconnected the idle motor and it drops. I know you said it should spike. Do you think someone somewhere messed up wiring on this car? Should i just order another idle motor and give it a try?

Thanks for your help

[82DMC12]

found the wide open switch is not connected to anything(i think thats what it is) the other 2 open plugs on the left side are for something to do with an automatic right?
the deeper i go the more i find.
cold start this morning and idle jumps to 2100. same as before. I disconnected the idle motor and it drops. I know you said it should spike. Do you think someone somewhere messed up wiring on this car? Should i just order another idle motor and give it a try?

Thanks for your help

The white plug for the full throttle switch should connect with the white plug you see in the second photo, however that cannot cause your high idle.

If the idle goes to 2100 RPM, that sounds like what happens when you disconnect the inner plug on the Idle ECU (the one that has 4 wires going into it). Check that plug and make sure none of the wires have backed out of the white plug so they aren't making connection.

If my car is idling normally, and I pull that plug off, the idle jumps up to around 2100.

[Ron]

found the wide open switch is not connected to anything(i think thats what it is) the other 2 open plugs on the left side are for something to do with an automatic right?
the deeper i go the more i find.
...
The Wide Open Switch wires are: Black and Light Green.
The Idle Speed Switch wires are: Black and Black with Light Green tracer.
The Kick Down Switch wires are: Black and Light Green with Green tracer.

[glockworks21]

The white plug for the full throttle switch should connect with the white plug you see in the second photo, however that cannot cause your high idle.

If the idle goes to 2100 RPM, that sounds like what happens when you disconnect the inner plug on the Idle ECU (the one that has 4 wires going into it). Check that plug and make sure none of the wires have backed out of the white plug so they aren't making connection.

If my car is idling normally, and I pull that plug off, the idle jumps up to around 2100.

i did that when mine was warmed up and idling normal and it jumped up like it should.

[glockworks21]

The Wide Open Switch wires are: Black and Light Green.
The Idle Speed Switch wires are: Black and Black with Light Green tracer.
The Kick Down Switch wires are: Black and Light Green with Green tracer.


thats all for automatics right? mine is a 5 speed.

[Ron]

That is for both. The plug with Black and Light Green with Green tracer is not used on manuals, if present.

[glockworks21]

So after cleaning and testing everything and all the research i came across a picture of throttle spool spring and realized mine was either an old style or something rigged up from previous owner. I changed out the spool spring and cold started it today and it jumped up for a second but then dropped down as soon as i threw a rev. then it hunted for about 30 seconds but stayed under 1k rpm. Huge improvement from before! Maybe something to do with what Parzival mentioned earlier in thread? tensions on the springs? Its only been one cold start try but i am hopeful its fixed.
Last question for the week hopefully, I ordered the other return spring(pic) seems as though I have to tear a lot apart to get to that bolt. Any suggestions on easy way to replace it?

Thanks


Dave T.

[82DMC12]

So after cleaning and testing everything and all the research i came across a picture of throttle spool spring and realized mine was either an old style or something rigged up from previous owner. I changed out the spool spring and cold started it today and it jumped up for a second but then dropped down as soon as i threw a rev. then it hunted for about 30 seconds but stayed under 1k rpm. Huge improvement from before! Maybe something to do with what Parzival mentioned earlier in thread? tensions on the springs? Its only been one cold start try but i am hopeful its fixed.
Last question for the week hopefully, I ordered the other return spring(pic) seems as though I have to tear a lot apart to get to that bolt. Any suggestions on easy way to replace it?

Thanks


Dave T.

In the first picture, you can increase the tension on the top spring for the throttle spool by holding the spring and lifting it out of the two channels it's currently in, and rotate the top of the spring clockwise so that it fits into the next pair of channels. Does that make sense?

In the second picture, you will need to remove the throttle body from the car in order to adequately service (grease) that spring. You'll have to remove the W-pipe, disconnect the two wires from the back of the idle speed microswitch, and disconnect the linkage from the lever that hits the idle speed microswitch. Remove the vacuum hose from the bottom of the throttle body. Then remove four allen cap screws to remove the throttle body with the black bellows attached. Now you can work on it on a bench.

Andy

[Rich]

Last question for the week hopefully, I ordered the other return spring(pic) seems as though I have to tear a lot apart to get to that bolt. Any suggestions on easy way to replace it?


Andy posted good answers for both of those springs.

The spring on the throttle butterfly shaft (much harder to replace than the spool spring) might not need attention. Yours doesn't look like a PO tried to grease it up and it looks pretty clean.

These springs don't "lose tension" over time so if it was installed correctly and is as clean as it looks then it's probably delivering the design torque to the shaft linkage already and there is little need for a new one. The coils seem to have space between them, not gunk, so very little friction there. To be extra sure you can blast its coils with aerosol brake cleaner right where it sits. Fully open the throttle linkage by hand to get at more of the coils for cleaning.

Final check: Does the throttle linkage arm with the "idle screw" on it now bottom out reliably against its stop every time your foot's off the gas? And the idle control circuit is engaged in that condition? Then there's no need for mo-better springs.

[Elvis]

Did you already test a known good idle ECU ?

[glockworks21]

thank you for all the help. a lot was cleaned up and tested. I think the bulk of the problem was that tension on that old style throttle spring. The high idle seems to be fixed! I will be posting my next issue in a moment.. :o)

Thanks!