Idle Backwards

[82DMC12]

Well, I thought I had the idle issue solved. I don't completely. Sorry, but here is a list of questions to help me understand.

1. I thought the ECU ALWAYS controlled the RPMs at 775. If so, what does the idle throttle plate screw adjustment do? If you set it for high RPMs, the RPMs are greater than the 775. If you set it low, will the ECM maintain the 775 RPMs, or will it run at the lower RPM?
2. When does the ECM control the RPMs and when does the idle throttle plate control the RPMs?
3. The micro switch tells the car the engine should be at idle RPM, right?

Here's the problem. Engine starts fine hot or cold. RPMs are at 900 from the set screw/idle throttle plate. With the lights on, A/C on and in drive it drops to 775 RPMs. However, in neutral and not touching anything, I mean nothing, the idle will now and then go to 1,500 RPMs and after a while back to 900 RPMs. Any ideas?

I just replaced the Idle Speed Motor, Vacuum Hoses are all new. Micro switch is set and is working. Dwell is set. I will admit the engine runs a bit rough/vibrates at idle.

If you still think it might be the deacceleration valves/springs, where are they? If I take off the throttle body, will I see then and clean them with carburetor cleaner provided the issue is just grime?

Could it be the ECU or an issue with one of the inputs?

Answers:
1) ECU will always try to control the RPM's at 775 AT IDLE which means your foot is off the gas and the idle speed microswitch is depressed. It can't do this if the curb idle screw is not set correctly or there is some other vacuum leak, decel springs , etc.

2) ECU controls idle speed only at idle. It does nothing when your foot is on the gas.

3) Yes

If your idle microswitch is flakey, you have a bad wiring connection, or the screw is barely touching the switch, and the switch fails to close AT IDLE, the RPMS will go up to 1,300 or so.

The decel springs are in the throttle body, you can see them if you remove the W pipe from the front of the intake manifold. You can clean them with carb cleaner but they are almost certainly "OK" as long as the look like a coil and evenly spaced / not collapsed.

[Ricker]

Messing around trying to figure out the idle changing issue. I looked at the deacceleration springs and they look OK. I juggled the copper tube (tube of agony) from the ISM to the intake manifold. I think it is not sealed and is an air leak at the intake manifold. The engine RPMs changes. I remember years ago I put a new seal (metal ring with an O-ring in it). Even then I wondered if it really did a good seal. Is there a better way of sealing this? Some kind of RTV sealant with the O-ring thing, put the RTV on it and try to get it back in the hole? What do you need to remove to help make it possible from experience?

I also think the throttle linkage is a bit off, but that is pretty straight forward.

[Bitsyncmaster]

Messing around trying to figure out the idle changing issue. I looked at the deacceleration springs and they look OK. I juggled the copper tube (tube of agony) from the ISM to the intake manifold. I think it is not sealed and is an air leak at the intake manifold. The engine RPMs changes. I remember years ago I put a new seal (metal ring with an O-ring in it). Even then I wondered if it really did a good seal. Is there a better way of sealing this? Some kind of RTV sealant with the O-ring thing, put the RTV on it and try to get it back in the hole? What do you need to remove to help make it possible from experience?

I also think the throttle linkage is a bit off, but that is pretty straight forward.

I used locktite to lock that holding washer in but as long as the correct O-ring is installed it should make a good seal. I also put some grease on the copper pipe which may also help with sealing.

[Ricker]

Well now I did it. After messing with a bunch of things, here is what it does now. When in drive, lights on, A/C on or both off, it idles nicely at the 775 RPMs. However, now when in Park it idles at 1,850 RPMs but consistently (that's an improvement). And this is with the throttle linkage disconnected and the throttle plates closed and the microswitch engaged. Will start all over tomorrow checking everything again. Stupid car!

[Ricker]

Well now I did it. After messing with a bunch of things, here is what it does now. When in drive, lights on, A/C on or both off, it idles nicely at the 775 RPMs. However, now when in Park it idles at 1,850 RPMs but consistently (that's an improvement). And this is with the throttle linkage disconnected and the throttle plates closed and the microswitch engaged. Will start all over tomorrow checking everything again. Stupid car!

Now I'm thinking that there is not an air leak. But with the throttle completely closed and high RPMs, there has to be fuel coming from the Cold Start Valve (CSV). I will check this tomorrow by pulling the electrical connection. If it is adding fuel even when the engine is hot, then it is the temperature sensor. But why would the ISM be open to allow fuel to the engine? How do the CSV and ISM tie together?

[Michael]

I doubt the CSV is leaking.

Have you pulled and checked the idle computer?

Also wouldn't be a bad idea to double check the curb throttle setting. This gets the idle close without the computer working so much.

And when you checked the microswitch, did you use the ohms setting? Sometimes the switch goes bad but may test good but it's turned into a giant resistor.

If you want to bypass the switch, I would imagine you could just short the terminals together and eliminate the switch for testing purposes. Someone tell me if that's a bad idea.

[82DMC12]

Also agree it is not the CSV leaking.

You need to first follow Dave's advice and make sure the pipe of pain is installed correctly and the o-ring is in place. Grease it with Red Rubber Grease. You can see the tip of the pipe poking into the air meter housing if you push down on the meter plate and look in with a flash light. Make sure you can see all of the beveled edge inside the air meter.

The throttle can act screwy when you don't have the linkage installed. The springs in the throttle spool are supposed to help close the throttle butterflies. I think you need to start at the throttle butterfly and reset all of your linkage. Here are some tips, and do this in order since the order is important:

• Confirm the throttle cable is in excellent shape and not shredding where it comes out of the black sheath in front of the spool. Replace the inner cable if at all questionable, this is a safety item. You can easily replace it by pushing a new cable up from the gas pedal footwell.
• Disconnect the throttle cable from the spool and disconnect the linkage arm from the bottom of the spool
• Back off both idle stop screws (curb idle and microswitch screw) so they are not influencing anything else
• with the linkage disconnected, clean and then grease the springs both on the butterfly rod and the throttle spool with white lithium grease so you are sure they are not binding.
• Make sure the throttle arm (the thing with the two idle set screws in it) is centered on the threaded rod for the butterflies and the nut that holds it on is tight. Make sure the arm is not twisting on the rod because it's loose. That will give unpredictable results.
• connect the throttle linkage to the spool. Shorten it sufficiently so that the idle stop finger on the spool is about 1/4" away from the stop post. It is NOT supposed to be touching the post.
• Now with the W pipe off, turn the spool to full throttle (so the full throttle finger is actually touching the stop) and make sure the butterflies are opening completely at full throttle. You won't be able to make them open exactly perpendicular, but they will be just short of fully opening. Move the full throttle switch away from the FTS finger if it's interfering with the throttle spool itself hitting the stop.
• Now wrap around and connect the throttle cable to the spool smartly so that is somewhat taut but not affecting the throttle spool position. Do not try to take up all the slack. The cable shouldn't be loose but it can't be tight either.
• Disconnect the linkage arm from the bottom of the spool and shorten it about 2mm. You should have to open the throttle SLIGHTLY by turning the throttle spool in order to get the linkage arm is connect to the ball underneath. There has to be some pre-tension here.
• Now the throttle is basically set up. Screw in the microswitch screw so it definitely engages the idle speed switch and give it another half turn and lock it down.
• Start the car and it should be idling at 775. Wait until the engine is HOT and then slowly turn the curb idle screw IN , a tiny bit at a time, until it contacts the curb idle stop plate. Now each time you turn the curb screw in, do the same amount for the idle speed switch screw so that the pressure is even on both screws.
• Keep doing this SLOWLY until you can hear the engine idle speed increase due to the curb idle screw being too far in. Back it off so it is just on the edge of opening the throttle (increasing idle speed). Lock the curb idle screw down.
• Unscrew the idle switch screw until it opens the idle switch and RPM's go up to 1,300 - 1,700 (switch is off). Now turn it back in until the switch is engaged, and give it an additional 3/4 turn. Now lock it in.
• Now using the ferrule that the throttle cable runs through before going to the spool, loosen the lock nut and adjust the ferrule until the throttle cable is, once again, somewhat taut but not slack and not able to pull on the spool at rest. Now lock the nut down.

Throttle should be adjusted properly now. If you come to a stop sign and sometimes the idle is SLIGHTLY too high, you need either SLIGHTLY loosen the ferrule or SLIGHTLY back off the curb idle screw. That will correct intermittent BARELY elevated idle at stop signs etc.

[Ricker]

Spent today checking everything again. First, did the throttle adjustment like suggested above (lots of detail!). Long story short the microswitch is bad. When the engine is idling ONLY, I jumper it out and the RPMs came down. Second, I noticed when the engine is cold, RPMs are correct but go to 775 right away, like in 3 seconds. When the engine gets hot the RPMs increase without doing anything. So, I stop the engine while hot, pulled the plug on the thermotime switch and checked the ohms. With the ground to the engine block, one pin read 59 ohms the other 117 ohms (I thought this is supposed to be 0). Ok, so did I do something wrong or is the switch bad? Just to check thermotime switch is the one on the front of the engine (back of the car) and down by the water pump? Also, this switch would change the RPMs dependent on the engine temperature, right?

Are these only available from a Delorean parts guy?

[Michael]

Not sure about thermotime readings but it doesn't matter. That doesn't affect idle anyway. In fact, many people simply unplug it in the summer temps.

I think you found a major piece with the microswitch. Once curb idle is set and the switch is replaced you can start more on zeroing in on the culprits.

The two things that come to mind are (as I said before), bad ecu and/or intake leak. I don't really know the history of the car so I'm just throwing out common possibilities. Also don't forget the early advice of sticking or dirty throttle components/cable.

[Ricker]

I started the car in Park. Pulled the plug on the Thermo Time Switch. Jumpered the Microswitch. The Curb Idler Screw is not touching. The Butterflys are completely closed (I removed the U-Pipe and checked).
Once the car got hot the RPMs went up from 775 to 1,500. It starts find when hot. I pulled the center side plug on the ECU and the RPMs went up to 2,200. Plugged it back in and down to the 1,500 (cause the engine was hot). Plugged the Thermo Time Switch back in, made no changes.

Something is telling the car when hot to increase the idle RPMs. What? The ECU, some sensor? Why only when hot?