While AC on, Engine Bogs Down

[Trstno1]

Hey guys -

Looking to bounce some ideas off you. When my AC compressor kicks on, my engine seems to bog down. So if I set the engine to idle at 750 RPM as it should, when the compressor kicks in the car will idle down somewhere between 550 - 600 RPM making things pretty shaky because it wants to die. Turn AC off, engine returns to 750 RPM and all is right with the world. So....I have adapted to raising my idle to about 900 RPM when I want to use the AC so that when the compressor kicks in the idle bogs down to about 700...still a little shaky but ok.

What could be causing such a bog down? Is this a sign of a compressor going out? a bad idle speed unit? I know the engine will normally bog down with the compressor running, but it should be compensating for the additional load and allowing more air into the system to maintain the idle. Why would it not be?

I just want to fix this once and for all. I spent a long time getting my car to idle properly at 750 RPM and now I'm purposefully mucking it up just to have AC.

As always,

Any and all help is much appreciated

[bytes311]

My engine would actually die with the AC on. The problem was my regulator had gone bad so the alternator couldn't keep up. I replaced the alternator and the problem went away. I also installed modern radiator fans so the draw is considerably less now than with the stock fans.

[Bitsyncmaster]

A stock idle system you can not adjust idle speed (775 RPM) because the idle system will try to keep that RPM. If your adjusting the throttle open wider than the idle system can adjust than you can increase RPM.

It sounds like your idle system is not working. When you turn the key to on, does the idle motor buzz or vibrate?

[Ron]

Hey guys -

Looking to bounce some ideas off you. When my AC compressor kicks on, my engine seems to bog down. So if I set the engine to idle at 750 RPM as it should, when the compressor kicks in the car will idle down somewhere between 550 - 600 RPM making things pretty shaky because it wants to die. Turn AC off, engine returns to 750 RPM and all is right with the world. So....I have adapted to raising my idle to about 900 RPM when I want to use the AC so that when the compressor kicks in the idle bogs down to about 700...still a little shaky but ok.

What could be causing such a bog down? Is this a sign of a compressor going out? a bad idle speed unit? I know the engine will normally bog down with the compressor running, but it should be compensating for the additional load and allowing more air into the system to maintain the idle. Why would it not be?

I just want to fix this once and for all. I spent a long time getting my car to idle properly at 750 RPM and now I'm purposefully mucking it up just to have AC.

As always,

Any and all help is much appreciated It sounds like you are using the brass screw(s) to set your idle as in WS D:04:02-19. Some owners do this but D:01:13 says they are not to be used on a DeLorean because it has an electronic idle speed control system (idle speed motor, etc.). If that's the case, try fully seating the screws and see how it acts. (If no luck, you may want to inspect/wash the ISM out too.)

[Ron]

My engine would actually die with the AC on. The problem was my regulator had gone bad so the alternator couldn't keep up. I replaced the alternator and the problem went away. I also installed modern radiator fans so the draw is considerably less now than with the stock fans.I don't want to sidetrack the thread but mention that, if the alternator/regulator was allowing a good battery to get low enough to kill the engine, then it would be because the ignition was suffering and you would also have trouble starting the engine immediately afterwards. (IE, if there was enough power in the battery to start the engine when it died, then it had way more power left than needed to keep it running.) The battery light should not have came on when the key was in the Run position OR turned on as soon as soon as the alternator was unable to keep up.

[Trstno1]

It sounds like you are using the brass screw(s) to set your idle as in WS D:04:02-19. Some owners do this but D:01:13 says they are not to be used on a DeLorean because it has an electronic idle speed control system (idle speed motor, etc.). If that's the case, try fully seating the screws and see how it acts. (If no luck, you may want to inspect/wash the ISM out too.)
You are exactly right. I was adjusting the brass screws in order to give me a little more air into the system, thus raising the engine idle RPM. If I were to seat all of the brass screws like it should be, the engine will idle at 750 rpm just fine, but as soon as the AC compressor kicks on it bogs the engine down so much the car shakes. I'm trying to get that to stop happening... Understandably what I am doing is a band aid to get the results I need. I just need to trouble shoot why the engine would be bogging down in the first place when the compressor kicks on.

[Trstno1]

I don't want to sidetrack the thread but mention that, if the alternator/regulator was allowing a good battery to get low enough to kill the engine, then it would be because the ignition was suffering and you would also have trouble starting the engine immediately afterwards. (IE, if there was enough power in the battery to start the engine when it died, then it had way more power left than needed to keep it running.) The battery light should not have came on when the key was in the Run position OR turned on as soon as soon as the alternator was unable to keep up.

I have no issues with either the battery or alternator. When the car is running I am charging at nearly 14 volts. If I were to guess, I would say my Idle speed motor is not reacting quick enough. Which sucks, because I had just replaced it about a year or two back....

[Ron]

I have no issues with either the battery or alternator. When the car is running I am charging at nearly 14 volts. If I were to guess, I would say my Idle speed motor is not reacting quick enough. Which sucks, because I had just replaced it about a year or two back....Good. (I just mentioned that because his alternator shouldn't have caused his to die w/o the other symptoms he didn't mention....maybe clear something up/not your D's problem, imho.)

How are you "setting the idle"??

[Trstno1]

Good. (I just mentioned that because his alternator shouldn't have caused his to die w/o the other symptoms he didn't mention....maybe clear something up/not your D's problem, imho.)

How are you "setting the idle"??

I have just realized that if you open the brass screw closest to the middle of the engine and adjust the other two a bit, I can get the idle RPM of my car to increase from the 750. I really don't want that to be the focus here. I will be re-torqueing the brass screws down to a closed position and start the troubleshoot from there. When the brass screws are where they should be, the engine idles fine at 750 - 775.

how quick should the idle speed motor react to the ac compressor kicking on? And is there a chance I could have some sort of vacuum leak only when the ac is on?

ideas?

[Ron]

I have just realized that if you open the brass screw closest to the middle of the engine and adjust the other two a bit, I can get the idle RPM of my car to increase from the 750. I really don't want that to be the focus here. I will be re-torqueing the brass screws down to a closed position and start the troubleshoot from there. When the brass screws are where they should be, the engine idles fine at 750 - 775.

how quick should the idle speed motor react to the ac compressor kicking on? And is there a chance I could have some sort of vacuum leak only when the ac is on?

ideas?Sorry, I missed post #6.
Good!

The ISM should react ~instantaneously and settle down quickly, eg, as when you tap the throttle lightly.

Yes, when the AC is on, the Mode Switch and anything it de/activates are good candidates for vacuum leaks.
Good thinking!
Try removing its vacuum feed line at the intake manifold and cap the port off.

Load the ISM with carb spray and shake it so that the rotor gets a good workout, when clean, repeat with WD or similar lube...

[David T]

The ability of the idle motor system to control the idle (if it is working) is reduced when you open the brass air screws, have vacuum leaks, don't have the screws on the throttle arm set correctly, and so on. The A/C will reduce the idle but if the idle motor system is working as it should, it will compensate for it. As also mentioned, if the idle gets too low and/or the electrical system is not working at full capacity, the motor will die. A lot of chain auto stores will test your alternator and battery for free. If the battery is over 5 years old it is probably due for replacement. Make sure the alternator belt is not slipping. Do you hear any metallic or clunking noises when you run the A/C? If the system is overcharged with refrigerant, it can stall the motor.

[bytes311]

I don't want to sidetrack the thread but mention that, if the alternator/regulator was allowing a good battery to get low enough to kill the engine, then it would be because the ignition was suffering and you would also have trouble starting the engine immediately afterwards. (IE, if there was enough power in the battery to start the engine when it died, then it had way more power left than needed to keep it running.) The battery light should not have came on when the key was in the Run position OR turned on as soon as soon as the alternator was unable to keep up.

It has been a few years and I forgot all of the details until I just now re-read my old thread on the subject (http://dmctalk.org/showthread.php?15482-Alternator-Light). At the time I still had the original Ducellier and my battery light was non-functional.

[Ron]

Cool! ...I thought something was missing, just didn't know what. :)

[Trstno1]

ok -

So I completed a couple of tests. It seems as though the culprit are my stock radiator fans. If I pull the fuses on my solid state relay so that the fans don't kick on when the AC compressor kicks on the engine bogs a tiny bit, but the ISM reacts and the engine compensates quickly. However, If I have the additional load of the fans while the compressor kicks on engine bogs down quite a bit. I have the hervey ground kit, and have cleaned up all other grounds so I feel the grounding of the car is good. I wonder if those fans are just pulling too much current for the system.... Maybe time for new rad fans and shroud.

I still need to complete the vacuum test at the manifold.

[Bitsyncmaster]

ok -

So I completed a couple of tests. It seems as though the culprit are my stock radiator fans. If I pull the fuses on my solid state relay so that the fans don't kick on when the AC compressor kicks on the engine bogs a tiny bit, but the ISM reacts and the engine compensates quickly. However, If I have the additional load of the fans while the compressor kicks on engine bogs down quite a bit. I have the hervey ground kit, and have cleaned up all other grounds so I feel the grounding of the car is good. I wonder if those fans are just pulling too much current for the system.... Maybe time for new rad fans and shroud.

I still need to complete the vacuum test at the manifold.

You do know good connections (ground and power) will result in higher current draw from your fans. I know some people think high current draw is due to bad grounds but that is not true for non-electronic loads.

I always recommend OEM fans get replaced with new lower current fans. Some alternators don't put out enough current at idle speed.

[Ron]

Back on track-
The ISM should compensate for the load that the alternator or anything else puts on the engine, when idling in neutral. If the fans are drawing an excessive amount, then the battery would suffer, not the RPM. If you plug all of the vacuum line (shut the brass screws) and turn the A/C on, the RPM should return to normal after a short reaction time. If not, the ISM is unable to do its job for some reason. Usually it caused by: dirty ISM, vacuum leak, ISM related electrical problem. (I doubt the latter.)

[David T]

If the alternator can't put out enough power at idle when the fans start up, the excessive drop in voltage will mess with the ignition system and the idle motor causing the drop in RPM's. Could be a bad battery, bad connections, or a bad alternator. If you have the Ducey alternator it should be replaced and if the battery doesn't have enough capacity (or is old) it should be replaced. When the OEM fans start up (and they both start up at the same time) it is a BIG load on the electrical system and if there is anything faulty in the electrical system you will notice it then, especially if the A/C is also on. Then you have the additional load of the cabin fan motor and the clutch coil for the compressor. The Fanzilla was designed to sequence the fans to try to reduce the load on the electrical system. Today you have the option of upgrading the fans to ones that are much more efficient and don't draw as much power while still moving the same amount of air. While switching the fans will help, I consider that a Band-Aid, you are not really fixing the problem, just the symptom. The real fix is to figure out what's wrong with your electrical system so it can handle the load.

[Trstno1]

If the alternator can't put out enough power at idle when the fans start up, the excessive drop in voltage will mess with the ignition system and the idle motor causing the drop in RPM's. Could be a bad battery, bad connections, or a bad alternator. If you have the Ducey alternator it should be replaced and if the battery doesn't have enough capacity (or is old) it should be replaced. When the OEM fans start up (and they both start up at the same time) it is a BIG load on the electrical system and if there is anything faulty in the electrical system you will notice it then, especially if the A/C is also on. Then you have the additional load of the cabin fan motor and the clutch coil for the compressor. The Fanzilla was designed to sequence the fans to try to reduce the load on the electrical system. Today you have the option of upgrading the fans to ones that are much more efficient and don't draw as much power while still moving the same amount of air. While switching the fans will help, I consider that a Band-Aid, you are not really fixing the problem, just the symptom. The real fix is to figure out what's wrong with your electrical system so it can handle the load.

What do you think could be wrong with the electrical system if you had to guess. It took some time, but I finally upgraded the fans to the ones from DPI and I have a Hervey type grounding system. The. Engine bogs down much less than before, but it still does. How long should it take for the ISM to adjust to the change? Also, could I just have a bad A/C compressor? It’s almost the last thing I have not replaced yet....

[David T]

Start by checking that you have the "Relay Upgrade Kit" with the uprated circuit breakers. Remove the blue fan fail relay if you still have it and replace it with either a solid state controller or the fan fail bypass wires. Check all of the connections to the fans on the power side AND ground side. After you do all of that, find and fix all of the vacuum leaks. Vacuum leaks reduce the power (effect) of the idle motor, preventing it from increasing the idle to compensate for the additional load of the A/C. The idle motor can also be sticking making it slow to react. That can be fixed by cleaning it with some solvent. Then there are some "oddball" things to check like the decel springs. If they are deformed and not holding the valves closed on the throttle plates, that would mess up the idle. Do you really use the A/C in Alaska?

[dn010]

It may not have anything to do with your electrical system and more to do with the condition of your AC system. My AC system would kill the engine if I let off the clutch coasting to a stop. Lack of oil or the wrong amount of refrigerant will cause the compressor to stress. I noticed David mentioned this but no follow up to it. You might hook up some gauges and confirm what your pressures are before replacing everything electrical.

[Trstno1]

Start by checking that you have the "Relay Upgrade Kit" with the uprated circuit breakers. Remove the blue fan fail relay if you still have it and replace it with either a solid state controller or the fan fail bypass wires. Check all of the connections to the fans on the power side AND ground side. After you do all of that, find and fix all of the vacuum leaks. Vacuum leaks reduce the power (effect) of the idle motor, preventing it from increasing the idle to compensate for the additional load of the A/C. The idle motor can also be sticking making it slow to react. That can be fixed by cleaning it with some solvent. Then there are some "oddball" things to check like the decel springs. If they are deformed and not holding the valves closed on the throttle plates, that would mess up the idle. Do you really use the A/C in Alaska?

Yes.. I have all new relays circa 2018. I also have DM's solid state lambda/RPM/Fan Fail Relay(2x fused). I also have his front relay ground bus but I have not installed it yet. I'll need to look into the circuit breakers as I cannot remember. What am I looking for in regard to those? All connections to fans are solid. I'm also pretty sure I don't have any vacuum leaks since the motor runs pretty good w/o AC. I had a new ISM and actually took it out and lubed it up with WD40 and tested it, so that's working. (I just don't know if it's reacting quick enough. The Decel springs seem good, and yes I definitely use the AC in Alaska. The last couple years in AK have been really hot. My wife requires the AC to be on if I want to take her anywhere in the D.

[Trstno1]

It may not have anything to do with your electrical system and more to do with the condition of your AC system. My AC system would kill the engine if I let off the clutch coasting to a stop. Lack of oil or the wrong amount of refrigerant will cause the compressor to stress. I noticed David mentioned this but no follow up to it. You might hook up some gauges and confirm what your pressures are before replacing everything electrical.

This could be the issue for sure. I have swapped to 134A, but I do have a small refrigerant leak. Every summer I put in about 2 cans of 134A and that gets me through the summer. Up until now I had other things on the repair list that was much more pressing than the AC system. I honestly thought the electrical surge from the OEM fans kicking on was the culprit for causing the problem. However, now that they are swapped to DPI's and the problem albeit better, is still there, the root cause must be different. I was thinking I should just replace all hoses and AC compressor. That way I solve the leak and put my mind at ease about it possibly being an AC compressor issue.

I also just purchased DM's microprocessor controlled idle ecu, so I could just program it to bump the idle by 100 rpm when the AC is on. I know, I know.... another band-aid. I actually would really like to find the root cause of the issue.

[David T]

If the compressor was that bad you would see the clutch slip or the belt slip/squeal. It would get very hot, and you wouldn't have enough cooling. It can't hurt to check the pressures. If you have a leak and have been constantly "topping off" you could be out of oil and that would make the compressor work very hard and eventually fail. Especially if you have the wrong oil for -134.

[dn010]

If the compressor was that bad you would see the clutch slip or the belt slip/squeal. It would get very hot, and you wouldn't have enough cooling. It can't hurt to check the pressures. If you have a leak and have been constantly "topping off" you could be out of oil and that would make the compressor work very hard and eventually fail. Especially if you have the wrong oil for -134.

My guess would be too much refrigerant especially if you're adding cans and don't know how much is in there. Manifold sets are cheap, under $30 on Amazon and is a good starting place before you toss some serious money at it. If you're running 134 on original hoses, that may be a source of your leak. Do you have any compressor noise with the AC on?

+1 about the oil.

[Trstno1]

If the compressor was that bad you would see the clutch slip or the belt slip/squeal. It would get very hot, and you wouldn't have enough cooling. It can't hurt to check the pressures. If you have a leak and have been constantly "topping off" you could be out of oil and that would make the compressor work very hard and eventually fail. Especially if you have the wrong oil for -134.

I changed the oil when I did the 134A swap, but maybe its low. I'll check the pressures and get back.

[Trstno1]

My guess would be too much refrigerant especially if you're adding cans and don't know how much is in there. Manifold sets are cheap, under $30 on Amazon and is a good starting place before you toss some serious money at it. If you're running 134 on original hoses, that may be a source of your leak. Do you have any compressor noise with the AC on?

+1 about the oil.

I am running original hoses and completely understand that the 134A is probably just leaking out of it. Yet another reason I thought replacing the hoses would be a good idea. I do have a manifold set from when I originally did the work. I'll hook it back up and report back with the pressures. Though, even when I did my original 134A conversion my book values for pressures were pretty much spot on and the engine still bogged down when the AC compressor turned on. Let me get the pressures and I'll get back and we can go from there.

[Trstno1]

So, I took out the gauges and checked the static pressure at 67psi on the low and 63ish psi on the high. It is 69 degrees F, so about 20.5 degrees C.

Once i started the car and turned on the AC, the compressor kicks On with low side at 47 psi and the high side at 85 Psi.

The low pressure gauge seems high
The high pressure gauge seems low

The online resources I have interprets such results as “AC needs service, possibly faulty compressor”.

Cycle time is 6.5 seconds off, 14.5 seconds on. What should the correct cycle time be?

Also, I have a 100RPM drop when the compressor kicks on. The ISM seems to compensate fairly quickly, but not before I feel the RPM drop and engine vibration. Note that this problem is only witnessed at idle. I usually purposefully turn off my AC if I am at a stop light so I don’t witness the engine bog down. With the current cycle rate I’ll get that bog down at least 2-4 times per light. Quite un-desirable when you are trying to look cool next to other cars.

What do you guys think?

Note: RPM drop prior to the new fans were more like 200-250 RPM, so I’m getting there, just not there quite yet.

[Ron]

So, I took out the gauges and checked the static pressure at 67psi on the low and 63ish psi on the high. It is 69 degrees F, so about 20.5 degrees C.

Once i started the car and turned on the AC, the compressor kicks On with low side at 47 psi and the high side at 85 Psi.

The low pressure gauge seems high
The high pressure gauge seems low

The online resources I have interprets such results as “AC needs service, possibly faulty compressor”.

Cycle time is 6.5 seconds off, 14.5 seconds on. What should the correct cycle time be?

Also, I have a 100RPM drop when the compressor kicks on. The ISM seems to compensate fairly quickly, but not before I feel the RPM drop and engine vibration. Note that this problem is only witnessed at idle. I usually purposefully turn off my AC if I am at a stop light so I don’t witness the engine bog down. With the current cycle rate I’ll get that bog down at least 2-4 times per light. Quite un-desirable when you are trying to look cool next to other cars.

What do you guys think?

Note: RPM drop prior to the new fans were more like 200-250 RPM, so I’m getting there, just not there quite yet.
The static pressure for R12 and 134a @ 70°F ambient is ~70psi. The reading must be taken after the system has been allowed to cool off completely (overnight). The high and low sides will always be the same in this state regardless of the ambient temp. (They will balance via the orifice tube. So your gauges are a tad off.) Static pressure will only tell you if there is 'some' refrigerant -- Over or undercharged systems will read the same.

You should take readings when the compressor cycles OUT/OFF and refer to the chart at N:09:01 in the WSM.
When the compressor kicks in at 70°F ambient, the high side should rise from 70 psi to 125-150 psi while the low side falls from 70 psi to 25-32 psi, causing the clutch to cycle off. (134a will have higher high side pressures.)

The cycle times are affected by everything from system condition to humidity. Theoretically, the system may not cycle at all under the right conditions -- Use the cut out pressures found using the procedure above for anything useful.

------

Did you try plugging the main vacuum feed as suggested above?

[Bitsyncmaster]

A lot of people post "Bogs Down" with AC on and most of us think your engine has no power with AC running. In reality the AC only requires about 5 hp. to run so it seems most people say bogs down because the idle RPM drop. This is usually a problem with the idle system and not a problem with the AC.

Your 85 PSI high side does sound to low and would indicate a low charge or bad compressor but do as Ron suggested and take those readings when the compressor has just kicked off.

[Trstno1]

A lot of people post "Bogs Down" with AC on and most of us think your engine has no power with AC running. In reality the AC only requires about 5 hp. to run so it seems most people say bogs down because the idle RPM drop. This is usually a problem with the idle system and not a problem with the AC.

Your 85 PSI high side does sound to low and would indicate a low charge or bad compressor but do as Ron suggested and take those readings when the compressor has just kicked off.

The readings I got when the compressor kicks off was 25 for the low side and 120 for the high. So I suppose those readings just point towards adding more refrigerant. However, I know I have a leak simply due to the fact I need to keep topping it off occasionally. And the fact that I am using original hoses with 134A. But when I do have enough refrigerant in the system, the AC blows cold. Right now it is blowing cold.

My problem is the sudden RPM drop when the compressor kicks on. Before the new DPI fans I would idle at 775rpm and when the compressor would kick on it would drop to like 550rpm. Big dip! Now with the new fans I would say its only dropping about 100 rpm but still noticeable when at an idle since the engine labors and vibrates. I have tested the ISM, and it is compensating about a second after the rpm dip, and then the rpm returns to 775 like it should. So my idle system seems to be working as it should.

I guess I was hoping I could do something so that I wouldn’t even feel the initial 100 rpm drop at all. Does everyone else feel the engine vibrate the car when the AC compressor kicks on? Is it just the normal operation of the Delorean?

[Bitsyncmaster]

The readings I got when the compressor kicks off was 25 for the low side and 120 for the high. So I suppose those readings just point towards adding more refrigerant. However, I know I have a leak simply due to the fact I need to keep topping it off occasionally. And the fact that I am using original hoses with 134A. But when I do have enough refrigerant in the system, the AC blows cold. Right now it is blowing cold.

My problem is the sudden RPM drop when the compressor kicks on. Before the new DPI fans I would idle at 775rpm and when the compressor would kick on it would drop to like 550rpm. Big dip! Now with the new fans I would say its only dropping about 100 rpm but still noticeable when at an idle since the engine labors and vibrates. I have tested the ISM, and it is compensating about a second after the rpm dip, and then the rpm returns to 775 like it should. So my idle system seems to be working as it should.

I guess I was hoping I could do something so that I wouldn’t even feel the initial 100 rpm drop at all. Does everyone else feel the engine vibrate the car when the AC compressor kicks on? Is it just the normal operation of the Delorean?

Try turning the curb idle screw clockwise about a 1/4 to 1/2 a turn. The curb idle screw is the lower screw on the throttle arm.

[MrChocky]

The readings I got when the compressor kicks off was 25 for the low side and 120 for the high. So I suppose those readings just point towards adding more refrigerant. However, I know I have a leak simply due to the fact I need to keep topping it off occasionally. And the fact that I am using original hoses with 134A. But when I do have enough refrigerant in the system, the AC blows cold. Right now it is blowing cold.

My problem is the sudden RPM drop when the compressor kicks on. Before the new DPI fans I would idle at 775rpm and when the compressor would kick on it would drop to like 550rpm. Big dip! Now with the new fans I would say its only dropping about 100 rpm but still noticeable when at an idle since the engine labors and vibrates. I have tested the ISM, and it is compensating about a second after the rpm dip, and then the rpm returns to 775 like it should. So my idle system seems to be working as it should.

I guess I was hoping I could do something so that I wouldn’t even feel the initial 100 rpm drop at all. Does everyone else feel the engine vibrate the car when the AC compressor kicks on? Is it just the normal operation of the Delorean?

My car does shake a bit at idle, A/C or no - although less so after changing plugs etc. My problems are different, but I'm reading this with interest just to see how everything is interconnected. My next task is to change
vacuum hoses, but you might be interested in the commentary:

http://dmctalk.org/showthread.php?18301-Strange-intermittent-start-up-behavior

[Trstno1]

Try turning the curb idle screw clockwise about a 1/4 to 1/2 a turn. The curb idle screw is the lower screw on the throttle arm.

all 3 brass screws are closed.

[Trstno1]

My car does shake a bit at idle, A/C or no - although less so after changing plugs etc. My problems are different, but I'm reading this with interest just to see how everything is interconnected. My next task is to change
vacuum hoses, but you might be interested in the commentary:

http://dmctalk.org/showthread.php?18301-Strange-intermittent-start-up-behavior

I appreciate the reply. I've definitely been down the vacuum line rabbit hole. good luck!

[Trstno1]

Try turning the curb idle screw clockwise about a 1/4 to 1/2 a turn. The curb idle screw is the lower screw on the throttle arm.

My apologies......I misunderstood what you meant. Before, the only way I messed with the idle was when I was messing around with the brass screws. I'll attempt turning the curb idle screw when I get home. That will just raise the idle ever so slightly so I don't notice the 100rpm dip? Essentially idling at 875, then dipping down to 775 for a slight second when the AC compressor kicks on? If so, your ECU will essentially do the same thing right?

[Bitsyncmaster]

My apologies......I misunderstood what you meant. Before, the only way I messed with the idle was when I was messing around with the brass screws. I'll attempt turning the curb idle screw when I get home. That will just raise the idle ever so slightly so I don't notice the 100rpm dip? Essentially idling at 875, then dipping down to 775 for a slight second when the AC compressor kicks on? If so, your ECU will essentially do the same thing right?

No it will not change the idle from 775 unless you adjust it to far. What it will do is make the idle motor run more closed but you want to have that adjusted closer to where it will still hold 775 on a hot engine with the idle motor almost closed. I adjust it on a hot engine by turning it clockwise until the idle RPM goes above the 775 then back it off a little.

My ECU you can set the idle RPM from 775 to 1000 RPM.