Idle Speed Motor ***SPLIT from Liner Seals***

[DMCVegas]

No, ...misunderstanding(s).
I think I'm with you now- When you "take the IAC motor out of the system..." you block off its passage, making it ~Basic K-Jet instead of K-Jet with lambda. Then open the screw so it gets enough air to run.... Which means the air is still measured by the plate (but not necessarily the amount the system expects after you set it, similar to the procedure in D:04:01 where the O2 sensor is disconnected....). Yes?

All air that is delivered to the Idle Speed Circuit is pulled in after the Fuel Metering plate. The inlet is below the plate. All air is metered and accounted for to maintain AFR. The problem with removing the Idle Speed Motor is that there is no Auxiliary Air Valve to compensate for fast idle conditions.

With the original idle speed system, the K-Jetronic manifold here was designed to use 3 brass screws and a balancing tube. Take a look:

prv-drawing.jpg

You'll notice that aft of the butterflies on those 90° manifold tubes, there is an additional tube plumbed in which connects both sides. The 3 screws that are present in the manifold for adjusting Idle Speed are first a feeder screw, and the final two being for the left and right cylinder banks. The tube that was included above on this earlier system allows for ΔP to occur in order for the engine to naturally correct the volumes between both cylinder banks for proper emissions. It also connected to the oil filler cap for crankcase ventilation.

Here is the problem with removing the Idle Speed Motor and using those screws to set Idle:

Once you set idle speeds, you're done. You cannot increase idle speeds beyond that point on a warmed engine. Once the advent of A/C became prevalent on cars, the additional load on the engine during idle could stall them. Thus manufacturers resorted to kicker solenoids on the carburetor throttle linkage assemblies to activate whenever the compressor clutch was engaged. But rather than install a kicker solenoid, BOSCH came up with this:

s-l225.jpg

Whenever the engine needs a fast idle condition, that valve slides open and allows additional air to bypass the throttle plates.

K-Jetronic is a modular system that accepts add-ons, and later on BOSCH came out with the updated microprocessor-controlled Idle Speed Motor that we use now. Instead of just blindly allowing air to pass through, it controls the amount through feedback and adjusts to 775± RPMs automatically.

So, if you're opting for utilizing the Idle Speed Screws instead, you need to either never use A/C again, or splice in an AAV to compensate. Even if you retain the stock idle speed control system, you have no way of properly balancing the left and right cylinder banks without measuring CO off of each manifold! The result is one side will be too lean, and the other too rich. Aside from LAMBDA now perpetually fighting your engine, you'll be robbed of power and may do other long-term internal damage to the engine.

LAMBDA also has noting at all to do with the Idle Speed system. LAMBDA only wants to measure O₂ content within the exhaust stream. It's adjustment points are within a bypass of the Primary Pressure Regulator on the Fuel Distributor by way of the Frequency Valve to control line pressures feeding the Fuel Injectors. The two systems are completely independent of on another.

Now there is another possibility for a malfunctioning Idle Speed Circuit: wiring. The test is simple though. Just test for continuity. Had this problem with my own car, grafted in a new wire to the ISM, and it worked just fine.

I also readjusted the Microswitch as well. The factory recommends setting the stop screw to only trigger the switch once the throttle plates are back at a fully closed position. Nope, that ain't happening. I lengthened the screw and bent the bracket up to bury that damn screw almost to the bottom without interfering with the throttles fully closing. The result was that the idle circuit triggered early and the RPMs would gently float down instead of rapidly falling. Same as a modern car, and far less voltage spikes from my alternator.

[David T]

Good post. More reasons why you should have an automatic way to maintain a stable idle speed include the fact that there is no damper on the throttle so on the 5-speed, if you let off the throttle quickly, the engine could stall as the butterfly plates snap shut. The idle also must be increased for a cold engine so it doesn't stall. While it may be tempting to remove a complicated sub system, it isn't that hard to get it to work.

[Ron]

All air that is delivered to the Idle Speed Circuit is pulled in after the Fuel Metering plate. The inlet is below the plate. All air is metered and accounted for to maintain AFR. The problem with removing the Idle Speed Motor is that there is no Auxiliary Air Valve to compensate for fast idle conditions.

Yes. That's the way I've understood it for years. FWIW, I was asking because "taking the ISM out of the system" left me wondering if he was replacing it with a pipe or blocking it off or ???... Seemed a pipe the size of the ISM inlet/outlet would let way to much pass, and if blocked off, the amount of air the brass screw allows to pass would be compensated for by the Idle Speed System when reinstalled....
[I think you will agree? Suppose with your engine's condition, ISM, Oil, ambient temp, fuel, etc, etc., set up per the manual, it idled at 750 RPM. (That's within spec.) If you block the ISM and open the brass screw to 750 RPM, the plate will not change, because the air was metered. The WUR/CPR will not change, so pressure/fuel will not change...Except the O2 sensor will see it go leaner, because more air than the butterflies were originally allowing is getting through. The frequency valve will add fuel causing the RPMs to rise. And the Idle Speed System will bring it back down to 750.
There may be more to it, but bottom line to me is, if you have 750 RPM and the CO is correct with the manual setup and the only real change made is the brass screw is opened, it has to be the ISM compensating for it. In other words, it works!

I've never saw (or noticed) a pic with the extra lines like those in the pic. COOL!
I've read where on some Volvos that, if the balancing screws are shut, the 3rd brass screw does nothing (ie it feeds them only), but I haven't tried it on one.

So, if you're opting for utilizing the Idle Speed Screws instead, you need to either never use A/C again, or splice in an AAV to compensate. Even if you retain the stock idle speed control system, you have no way of properly balancing the left and right cylinder banks without measuring CO off of each manifold! The result is one side will be too lean, and the other too rich. Aside from LAMBDA now perpetually fighting your engine, you'll be robbed of power and may do other long-term internal damage to the engine.

Not me, for reasons relate to what I sat and everything here. I just didn't have enough info on what was being tried....

I also readjusted the Microswitch as well. The factory recommends setting the stop screw to only trigger the switch once the throttle plates are back at a fully closed position. Nope, that ain't happening. I lengthened the screw and bent the bracket up to bury that damn screw almost to the bottom without interfering with the throttles fully closing.

I bent mine when I first got it. That allowed me to let the butterflies shut then turn the screw just enough to know it was not actually touching (carbs, TBs, whatever, I usually do it that way.) It looks like its broke off flush now. Like you, I have the switch setting heavy. Works for me...

======

+1 on good stuff....keep it going!
..I'm wondering what would happen if we separated WOT and Thermal Throttle Enrichment Switch circuits. Then had the WOT ground the connection for the O2 lead, which would push CO to 87° (27°-37° increase).
Maybe make it do some good holding the pedal to the floor when cold too, lol. (I'll have to think about that part ;-)

[Ron]

Ya guy's know I am going to have to sell this car, I just don't have the jack to keep it. But that being said I knew that when I bought it. Some people said sell it to someone who would love it and do a better job bringing it back to life. All I can say is I would drive my D anywhere after the work I have done on it! I am not a hack and this car is a Prime example of the D. On the upside I may have put myself in a position to actually own one that I can keep! Yes as incredible as it may seem I have a friend who has a friend who knows of another D with my name on it! Wish me luck as I am about to put 5051 up for sale. This is not a pitch but 5051 has a gorgeous underside and her topside is very very nice I am thinking of starting mid 40's any thoughts, Also everything on this car works from AC to Clock. I hope this does not violate any forum rules. It is not for sale yet! Couple light bulbs left to sort out!

Sorry for the slow reply, been fighting 2 Generac generators with problems along with the normal weekend BS...love learning/sharing, but I type too slow...

Yeah, cool stuff! -- A few thoughts above.
I'm curious as to how far the brass screw wound up being open? And if the CO dwell was correct when you reinstalled the ISM, first go? I'm going to guess it was.

RE: Forum rules- Since this thread is in the General Discussion section and its your thread, you can say most any thing you want...

[Ron]

Good post. More reasons why you should have an automatic way to maintain a stable idle speed include the fact that there is no damper on the throttle so on the 5-speed, if you let off the throttle quickly, the engine could stall as the butterfly plates snap shut. The idle also must be increased for a cold engine so it doesn't stall. While it may be tempting to remove a complicated sub system, it isn't that hard to get it to work.

+1

And I would say that goes for the entire system. But the electrical system is a different story!

[Giamanut]

All air that is delivered to the Idle Speed Circuit is pulled in after the Fuel Metering plate. The inlet is below the plate. All air is metered and accounted for to maintain AFR. The problem with removing the Idle Speed Motor is that there is no Auxiliary Air Valve to compensate for fast idle conditions.

With the original idle speed system, the K-Jetronic manifold here was designed to use 3 brass screws and a balancing tube. Take a look:

prv-drawing.jpg

You'll notice that aft of the butterflies on those 90° manifold tubes, there is an additional tube plumbed in which connects both sides. The 3 screws that are present in the manifold for adjusting Idle Speed are first a feeder screw, and the final two being for the left and right cylinder banks. The tube that was included above on this earlier system allows for ΔP to occur in order for the engine to naturally correct the volumes between both cylinder banks for proper emissions. It also connected to the oil filler cap for crankcase ventilation.

Here is the problem with removing the Idle Speed Motor and using those screws to set Idle:

Once you set idle speeds, you're done. You cannot increase idle speeds beyond that point on a warmed engine. Once the advent of A/C became prevalent on cars, the additional load on the engine during idle could stall them. Thus manufacturers resorted to kicker solenoids on the carburetor throttle linkage assemblies to activate whenever the compressor clutch was engaged. But rather than install a kicker solenoid, BOSCH came up with this:

s-l225.jpg

Whenever the engine needs a fast idle condition, that valve slides open and allows additional air to bypass the throttle plates.

K-Jetronic is a modular system that accepts add-ons, and later on BOSCH came out with the updated microprocessor-controlled Idle Speed Motor that we use now. Instead of just blindly allowing air to pass through, it controls the amount through feedback and adjusts to 775± RPMs automatically.

So, if you're opting for utilizing the Idle Speed Screws instead, you need to either never use A/C again, or splice in an AAV to compensate. Even if you retain the stock idle speed control system, you have no way of properly balancing the left and right cylinder banks without measuring CO off of each manifold! The result is one side will be too lean, and the other too rich. Aside from LAMBDA now perpetually fighting your engine, you'll be robbed of power and may do other long-term internal damage to the engine.

LAMBDA also has noting at all to do with the Idle Speed system. LAMBDA only wants to measure O₂ content within the exhaust stream. It's adjustment points are within a bypass of the Primary Pressure Regulator on the Fuel Distributor by way of the Frequency Valve to control line pressures feeding the Fuel Injectors. The two systems are completely independent of on another.

Now there is another possibility for a malfunctioning Idle Speed Circuit: wiring. The test is simple though. Just test for continuity. Had this problem with my own car, grafted in a new wire to the ISM, and it worked just fine.

I also readjusted the Microswitch as well. The factory recommends setting the stop screw to only trigger the switch once the throttle plates are back at a fully closed position. Nope, that ain't happening. I lengthened the screw and bent the bracket up to bury that damn screw almost to the bottom without interfering with the throttles fully closing. The result was that the idle circuit triggered early and the RPMs would gently float down instead of rapidly falling. Same as a modern car, and far less voltage spikes from my alternator.

I put the IAC back in after I set the IDLE I blocked it off just to get everything close to 750 RPM never was
a permanent removal!

[Giamanut]

Sorry for the slow reply, been fighting 2 Generac generators with problems along with the normal weekend BS...love learning/sharing, but I type too slow...

Yeah, cool stuff! -- A few thoughts above.
I'm curious as to how far the brass screw wound up being open? And if the CO dwell was correct when you reinstalled the ISM, first go? I'm going to guess it was.

RE: Forum rules- Since this thread is in the General Discussion section and its your thread, you can say most any thing you want...

Yes it came out pretty close and ended up the screw was not out but about a turn, so I just closed it to wee what would happen and it just kept Idle at 775 maybe had 10 RPM fluctuation but pretty nice!
my Percentage was bouncing around 45 to 55 but my digital meter is a little wank.

[Giamanut]

Good post. More reasons why you should have an automatic way to maintain a stable idle speed include the fact that there is no damper on the throttle so on the 5-speed, if you let off the throttle quickly, the engine could stall as the butterfly plates snap shut. The idle also must be increased for a cold engine so it doesn't stall. While it may be tempting to remove a complicated sub system, it isn't that hard to get it to work.

I didn't Remove any system just disabled it to set idle close! The IAC is fine I did not amputate it! Just easier setting worm Idle close so when I enabled the IAC it did not have to work much and the only brass screw opened is the Idle screw.
Just to clarify.

[Giamanut]

All air that is delivered to the Idle Speed Circuit is pulled in after the Fuel Metering plate. The inlet is below the plate. All air is metered and accounted for to maintain AFR. The problem with removing the Idle Speed Motor is that there is no Auxiliary Air Valve to compensate for fast idle conditions.

With the original idle speed system, the K-Jetronic manifold here was designed to use 3 brass screws and a balancing tube. Take a look:

prv-drawing.jpg

You'll notice that aft of the butterflies on those 90° manifold tubes, there is an additional tube plumbed in which connects both sides. The 3 screws that are present in the manifold for adjusting Idle Speed are first a feeder screw, and the final two being for the left and right cylinder banks. The tube that was included above on this earlier system allows for ΔP to occur in order for the engine to naturally correct the volumes between both cylinder banks for proper emissions. It also connected to the oil filler cap for crankcase ventilation.

Here is the problem with removing the Idle Speed Motor and using those screws to set Idle:

Once you set idle speeds, you're done. You cannot increase idle speeds beyond that point on a warmed engine. Once the advent of A/C became prevalent on cars, the additional load on the engine during idle could stall them. Thus manufacturers resorted to kicker solenoids on the carburetor throttle linkage assemblies to activate whenever the compressor clutch was engaged. But rather than install a kicker solenoid, BOSCH came up with this:

s-l225.jpg

Whenever the engine needs a fast idle condition, that valve slides open and allows additional air to bypass the throttle plates.

K-Jetronic is a modular system that accepts add-ons, and later on BOSCH came out with the updated microprocessor-controlled Idle Speed Motor that we use now. Instead of just blindly allowing air to pass through, it controls the amount through feedback and adjusts to 775± RPMs automatically.

So, if you're opting for utilizing the Idle Speed Screws instead, you need to either never use A/C again, or splice in an AAV to compensate. Even if you retain the stock idle speed control system, you have no way of properly balancing the left and right cylinder banks without measuring CO off of each manifold! The result is one side will be too lean, and the other too rich. Aside from LAMBDA now perpetually fighting your engine, you'll be robbed of power and may do other long-term internal damage to the engine.

LAMBDA also has noting at all to do with the Idle Speed system. LAMBDA only wants to measure O₂ content within the exhaust stream. It's adjustment points are within a bypass of the Primary Pressure Regulator on the Fuel Distributor by way of the Frequency Valve to control line pressures feeding the Fuel Injectors. The two systems are completely independent of on another.

Now there is another possibility for a malfunctioning Idle Speed Circuit: wiring. The test is simple though. Just test for continuity. Had this problem with my own car, grafted in a new wire to the ISM, and it worked just fine.

I also readjusted the Microswitch as well. The factory recommends setting the stop screw to only trigger the switch once the throttle plates are back at a fully closed position. Nope, that ain't happening. I lengthened the screw and bent the bracket up to bury that damn screw almost to the bottom without interfering with the throttles fully closing. The result was that the idle circuit triggered early and the RPMs would gently float down instead of rapidly falling. Same as a modern car, and far less voltage spikes from my alternator.

So like I said earlier The IAC is still there and working better than ever.
But I respectfully disagree with your first Paragraph. The sense plate Air Metering unit does not account for or even measure air, as it sends no signal to anything. It does allow a constant/Known amount of air to enter the engine for what ever position it is in. So knowing that opened half way it would allow for example would allow 300 cfm, it can be used to allow a correct amount of fuel in. It is a simple air actuated valve that allows a predetermined amount of fuel to flow to the injectors at a given position. The mixture screw is the stop it rest against and simply pushes it down to add more fuel. A/F is controlled by fuel pressure in open loop and Lambda is closed loop. CO setting does mostly nothing off idle. In closed loop CO is Lambda corrected.
IMHO. I could be wrong so I would not put a ton of stock in this post!

[Ron]

...
The sense plate Air Metering unit does not account for or even measure air, as it sends no signal to anything. It does allow a constant/Known amount of air to enter the engine for what ever position it is in. So knowing that opened half way it would allow for example would allow 300 cfm, it can be used to allow a correct amount of fuel in. It is a simple air actuated valve that allows a predetermined amount of fuel to flow to the injectors at a given position. The mixture screw is the stop it rest against and simply pushes it down to add more fuel. A/F is controlled by fuel pressure in open loop and Lambda is closed loop. CO setting does mostly nothing off idle. In closed loop CO is Lambda corrected.
IMHO. I could be wrong so I would not put a ton of stock in this post!

I wouldn't say the plate allows air in depending on its position. The amount of air determines the position of the plate, which is pressed in the opposite direction by the WUR/CPR. As you say, the position will determine the amount of fuel sent to the injectors by the FD. Then the Lambda system adjusts according to what it sees after it is burned, if it is in closed loop.