Attempting to destroy my idle lumpiness

[opethmike]

A perfect Delorean will have an idle that hunts.

Simply not true.

[NckT]

Simply not true.

I agree with opethmike, you can easily adjust the idle 'hunting fluctuations out, it's not hard to do either.

[Trstno1]

I agree with opethmike, you can easily adjust the idle 'hunting fluctuations out, it's not hard to do either.

Please tell me how to do it.

[dmruschell]

Simply not true.

Agreed.

Also, a lopey idle is separate from idle hunting. Aftermarket cams can have a lopey idle, and still maintain a fairly steady RPM (not hunting).

[opethmike]

Please tell me how to do it.

No vacuum leaks
Properly functioning lambda system
Proper idle fuel mixture

That's really all there is to it.

[David T]

Because you have several control systems and none of them synchronize with each other, there is no way to dampen oscillations except in the mechanical system they control. You have to understand control theory to know why this is true. One reason is that the control systems respond to the conditions AFTER they occur, don't correct quickly enough and over correct. That is one reason the idle spec is a plus-minus spec. The goal here is to make the engine run on each cylinder as equally as possible to keep any necessary corrections to a minimum to reduce over correcting. The bigger the correction the control systems must make, the larger the overshoot. Even so there will still be some hunting, especially when the motor is cold. That is why you hear some people say when they disconnect the idle system the engine runs smoother. That is because a control system (the idle control) over corrects. The two main control systems that are active when the motor is warmed up are the idle control and the Lambda system. They operate independently, their only connection is the mechanical system they both control. They both have cycles.

[dmruschell]

Because you have several control systems and none of them synchronize with each other, there is no way to dampen oscillations except in the mechanical system they control. You have to understand control theory to know why this is true. One reason is that the control systems respond to the conditions AFTER they occur, don't correct quickly enough and over correct. That is one reason the idle spec is a plus-minus spec. The goal here is to make the engine run on each cylinder as equally as possible to keep any necessary corrections to a minimum to reduce over correcting. The bigger the correction the control systems must make, the larger the overshoot. Even so there will still be some hunting, especially when the motor is cold. That is why you hear some people say when they disconnect the idle system the engine runs smoother. That is because a control system (the idle control) over corrects. The two main control systems that are active when the motor is warmed up are the idle control and the Lambda system. They operate independently, their only connection is the mechanical system they both control. They both have cycles.

I know Mike understands those systems, as do I. Minimizing the situations that need correcting by ensuring there are no vacuum leaks, the lambda system is working properly, and setting the idle fuel mixture correctly will virtually eliminate the overcorrecting that leads to idle hunting.

Both of my DeLoreans have performance camshafts and neither idle hunts when warm (and only one of them sometimes idle hunts when cold). I've fixed the idle hunting issue in a friend's DeLorean by adjusting the fuel mixture with a dwell meter.

A perfect DeLorean /may/ occasionally hunt at idle, but your statement that a perfect DeLorean /will/ hunt at idle is not true.

[opethmike]

Because you have several control systems and none of them synchronize with each other, there is no way to dampen oscillations except in the mechanical system they control. You have to understand control theory to know why this is true. One reason is that the control systems respond to the conditions AFTER they occur, don't correct quickly enough and over correct. That is one reason the idle spec is a plus-minus spec. The goal here is to make the engine run on each cylinder as equally as possible to keep any necessary corrections to a minimum to reduce over correcting. The bigger the correction the control systems must make, the larger the overshoot. Even so there will still be some hunting, especially when the motor is cold. That is why you hear some people say when they disconnect the idle system the engine runs smoother. That is because a control system (the idle control) over corrects. The two main control systems that are active when the motor is warmed up are the idle control and the Lambda system. They operate independently, their only connection is the mechanical system they both control. They both have cycles.

Uh, yeah, but the spec is +/- 50; not anything you are going to notice on either the tachometer, or the feel of the engine.

You should really stop just reading the manuals one of these days and try doing some actual work like those of us who know what we are talking about do. Maybe then someone might be interested in listening to you.

[NckT]

There are 2 independent systems, and both considered as fixed independent feedback PID control systems with 2 separate Process Variables (PV), fixed Setpoints (SP) fixed Proportional Integral, Derivative values contained within the circuit design.

However, looking at the system with my "Control Engineer" head on, the two Output (OP) are the frequency valve and the Idle control valve.

The main influence of the idle oscillation, other than the odd fire design is the output variable of the idle speed control valve with range 0 to 100% of the valve being 0 to 775 rpm. This control of the Output OP of the Isle control can be influenced such that the output control changed to 725rpm to 775 so full scale deflection of the valve adjusts this small idle range.

This is how I do it, applying experience and experimentation on my own D noting feedback values using oscilloscope to evaluate the feedback etc:

Gently screw all of the 3 brass screws down.
Unscrew the 2 brass screws nearest the throttle plate by 2 full tirns each.
Note the current average idle speed.
Unscrew the brass screw with the slot open until the idle speed is.higher than the previous reading, at this point screw it back in by half a turn.
Re check that the dwell of the idle computer is between 35 to 45 degrees. My preference is that the max.swing of the dwell is about 44
Turn engine off
Fit a metric feeler gauge with "30" in between the lower throttle body screw and its stop.
Adjust the top throttle stop so it just closes the microswitch. This adjustment is important to stop the timing of the idle valve from operating too soon or too late that can cause an off idle oscillation to critically dampen the idle response.

In effect, this adds an air bypass around the throttle plate and the opening of the 2 brass screws by a fixed amount adds the bypass as an air damped effect to critically damped the air flow, effectively changing the Integral of the control to critically dampen the oscillation.

The above assumes everything else is tested and working and that the control pressure and primary fuel pressure is correct and calibrated and that the oxygen sensor oscillates at least by approx 5 hertz at 3000 rpm. It'll also assume that the closing of the throttle is repeatable closed with no mechanical sloppiness.

Although not to "book" it makes the engine run right. I've done this procedure on 40 plus Deloreans at Tech events with oem config catalysed exhausts to performance exhausts with standard k jet to imported (to UK) "Stage 2" (ex Steve Wynnes car I believe) with the performance cams etc with repeatable results.

Feel free to follow the above, I'm happy to share the info to others. Yes, it's not to the 30 plus year old book but I'd rather go with experience and testing, analysis and repeatability of the control function change.

Good luck

NickT

[cis6409]

There are 2 independent systems, and both considered as fixed independent feedback PID control systems with 2 separate Process Variables (PV), fixed Setpoints (SP) fixed Proportional Integral, Derivative values contained within the circuit design.

However, looking at the system with my "Control Engineer" head on, the two Output (OP) are the frequency valve and the Idle control valve.

The main influence of the idle oscillation, other than the odd fire design is the output variable of the idle speed control valve with range 0 to 100% of the valve being 0 to 775 rpm. This control of the Output OP of the Isle control can be influenced such that the output control changed to 725rpm to 775 so full scale deflection of the valve adjusts this small idle range.

This is how I do it, applying experience and experimentation on my own D noting feedback values using oscilloscope to evaluate the feedback etc:

Gently screw all of the 3 brass screws down.
Unscrew the 2 brass screws nearest the throttle plate by 2 full tirns each.
Note the current average idle speed.
Unscrew the brass screw with the slot open until the idle speed is.higher than the previous reading, at this point screw it back in by half a turn.
Re check that the dwell of the idle computer is between 35 to 45 degrees. My preference is that the max.swing of the dwell is about 44
Turn engine off
Fit a metric feeler gauge with "30" in between the lower throttle body screw and its stop.
Adjust the top throttle stop so it just closes the microswitch. This adjustment is important to stop the timing of the idle valve from operating too soon or too late that can cause an off idle oscillation to critically dampen the idle response.

In effect, this adds an air bypass around the throttle plate and the opening of the 2 brass screws by a fixed amount adds the bypass as an air damped effect to critically damped the air flow, effectively changing the Integral of the control to critically dampen the oscillation.

The above assumes everything else is tested and working and that the control pressure and primary fuel pressure is correct and calibrated and that the oxygen sensor oscillates at least by approx 5 hertz at 3000 rpm. It'll also assume that the closing of the throttle is repeatable closed with no mechanical sloppiness.

Although not to "book" it makes the engine run right. I've done this procedure on 40 plus Deloreans at Tech events with oem config catalysed exhausts to performance exhausts with standard k jet to imported (to UK) "Stage 2" (ex Steve Wynnes car I believe) with the performance cams etc with repeatable results.

Feel free to follow the above, I'm happy to share the info to others. Yes, it's not to the 30 plus year old book but I'd rather go with experience and testing, analysis and repeatability of the control function change.

Good luck

NickT

Have to agree here , nicks advise is spot on ! I've had the pleasure of seeing Nick in action on many occasions on my own car and lots of others .the results speak for themselves .. the idle adjustment he describes works perfectly , it makes the idle so much smoother and throttle response is better to .
No more fluctuating at lights or junctions the needle comes to a stop right on the button no bouncing at all ,cold or hot , it idles like a modern car !
I've gone to lots of tech events in England and organised tech events here for the Irish club and he has come over to help us and done this adjustment on all our cars including a stage 2 hi lift cam spec car from Houston all with the same excellent results

He has shown and helped me understand k jet so much more easier to and has shown me how to rebuild and calibrate CPR and set up fuel pressure In the fuel distributor to optimize and bring it back to spec



Cheers
Shane