E38 idle tuning

Hymey, thanks for the follow on update... :cheers:

Wow. is all I can say!!! Thanks heaps Joel for taking the time and puting it in tradesman terms that I could understand. I have a couple of tweeks to go but the car idles like a stocker. Its a 224/224 on a 114.And the inprovment is out of sight. Make sme think a larger cam might be on the way. lol
Cheers Ian

Say yah! :) Great post Joel!

I just spent the last hr doing mine, See how she goes in the morning. I often have problems with the car stalling when i go from park to reverse out of my drive and have to foot brake and touch the go pedal.

I've noticed straight away that my spark idle is much more steady and no longer jumping from 15 to 5 degree's spark and sits nicely around 14'ish.

Thanks again for sharing Joel.

Thanks guys. I have learnt more on idle tuning over the past 6 months. Once hot running ilde is correct. We work on rpm dip. Ie rev the engine and watch how long it takes to settle. This is better to be slower then fast. It should gradually settle to idle. This prevents hunting to occur AND the rpms reduce slower on gear changes so the synchros have more time to catch up in M6 transmissions.

I will add some more to this looking at Cold start to the previous post. Just on a light note. What we find is that the engine needs cold start enrichment of 12.5 to 13.0:1 initially, and also in hot start.

Also timing needs to be looked at. There is a table that covers ECT add on for timing. If you start the engine in the morning and it needs more air, it is idling lower then commanded rpm and timing is high we can add on a substantial amount of timing similiar to what is commanding, also increase max idle air by a further 4%. Overall any changes that occur will require the idle to relearn which after several keystarts and driving it gets better and the long term trims will adjust precisely to what is required. So once the initial idle tune is in drive it for a couple of days and take not of what needs to be fine tuned before taking anymore major adjustments.

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Originally Posted by hymey

Step 1.

Drill a small hole in the throttle blade, 3 to 4mm, depending on the size of the cam. For stock cams bypass this step.

Reason for this is that the ETC TB only trims 0.4% at a time, this can be heard with the engine idling and in some cases a 0.4% change is to much and causes hunting of up to a difference of 100rpm. The min adjustment is 0.4% regardless of integral or proportion adjustment.

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Nice post mate, though Id argue that if your min airflow was correct you would be getting the required airflow past the blade anyway so wouldnt need to drill it.

I think your comments helped me sort out a cold start issue I had. It was 2 fold. First max area was set too low and secondly I was cutting too much timing out in the startup flair table.

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Originally Posted by ringram

Nice post mate, though Id argue that if your min airflow was correct you would be getting the required airflow past the blade anyway so wouldnt need to drill it.

I think your comments helped me sort out a cold start issue I had. It was 2 fold. First max area was set too low and secondly I was cutting too much timing out in the startup flair table.

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I appreciate your concern over drilling the throttle. What I stress is what I have written. The purpose of drilling it is not to increase min idle airflow. We do this by adjusting max idle air and min idle airflow. Read the post carefully I explain that it is drilled to create a buffer, It is there to create a bypass, when the throttle trims 0.4% with a camshaft the sound of the engine rpm shifting up and down can be heard, while this is OK for some it sounds horrible for me, So when the throttle trims some of the air is continually leaking through the throttle blade hole and only half of it is trimming between the throttle and the body. So it creates a buffer for air basically to take the easy way out but when the throttle trims back it reduces airflow past it and trims the air just nicely. 4mm seams to be on the money even 3mm is OK, 6mm while still OK means the body will have to trim to much back. Also the factory TB only commands 18.8% max in most OS at idle(sae.tp)

Believe me many many hours went into this. How does 2 years of trial and error sound going around in circles. I have been kind enough to share it to everyone for no price but just to cure the frustrations of it all and even if people don't understand why or how it works I have put it in simple format simply because it would take me days to go through it all and there is still more tricks I haven't shared as some of it is irrelevant. So I am very thankful to hear it has helped you. Even if you decide not to drill it thats your preference but if I did it for you and did the procedure I could get the idle better on your car. LS1s are a piece of cake compared to these, many w/s said the e38 was easy but the same cars they tuned had terrible idle. My obsessive compulsiveness drove me to get an easy way to do it so I can nail an idle in 15min before I even start tuning a customers car, Basically not to just achieve an idle but one they desire. I hope I have cleared this up. Drilling it is a very important procedure and the first part of it and not doing so will not achieve an idle to perfection.

But still Richard, thanks for posting and letting me know atleast it come of some help to you even if it was only a small part of it:) I have some more info to share shortly on it.

Great thread joel, this has helped me cure all of my idle problems, had a lot of undershoot and overshoot problems and stalling when trying to let the clutch out at idle(medium size cam)which i was beginning to think i would need to raise idle speed to help cure.

Thanks for laying it all out step by step too, makes for an easy reference...still having a fiddle to get the idle, and transition to idle perfect under all conditions,i'm willing to bet this thread has helped alot of people get an idle sorted quickly, not just guys like me tuning there own cars.
Jeez the old ls1 pcm was so much less complex than the E38 is

See query below...great explanation helps a lot !!!

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Originally Posted by hymey

Since this has been made a sticky, I have decided to follow on here. Basically I went in deep initially and maybe made things to confusing.

I have decided to simplify this. After helping Ian "alian" with his L76 idle today I thought it would be best to outlay some points. There is only a handful of steps and less then ten flashes of the pcm to obtain a rock steady idle.

The only complaints I ever get are that the 230s cam sounds like a 220s cam or 220s cam idles like stock.

The e38 has an amazing ability to control idle. Once idle is in place and correct everything else can fall into place. I know most people on here know how to tune afr and timing well. Idle is tricky but really its simple to obtain.

The first thing is to think old school. I am unsure how many of you guys have tuned an old small block with a dizzy. I can remember how good they idled for a basic carb and a set timing figure. Basically I am pointing out that very bland simple adjustments are to be taken in order to get the idle 99% right. Then altering some of the tables for drivability can be taken.

The purpose of this thread is not to setup throttle followers or crackers. The e38 is missing these. But in getting the idle correct, these characteristics fall into place and then the tables can be slightly changed in order to get a desired result.

Step 1.

Drill a small hole in the throttle blade, 3 to 4mm, depending on the size of the cam. For stock cams bypass this step.

Reason for this is that the ETC TB only trims 0.4% at a time, this can be heard with the engine idling and in some cases a 0.4% change is to much and causes hunting of up to a difference of 100rpm. The min adjustment is 0.4% regardless of integral or proportion adjustment.

This procedure isn't done to correct a bad idle , increase idle air or for plain sillyness like some do with LS1 TB but its to create a air bypass, A buffer ie if the throttle trims it's an abrupt airflow change and with a small hole some air will go through this and some will pass the edge of the butterfly it smooths airflow changes in TB movement and somewhat decreases the trimming effect of airflow and buffers the air movement which in our case is a good thing.


Step 2.

B1651 and B1652 these are both max idle area tables. One is for automatic transmissions when in gear the other for in neutral. I set these the same values. Having a higher max idle air for autos in N isn't required, min idle air covers this and also timing correction, The hard limit in the e38 is much lower then both the factory values anyhow.

We have to adjust this, it allows the correct idle airflow to be obtained.

In order to do this "min idle air" needs to be maxed out to 63g/s so that the pcm uses max idle area as its Throttle position %. So set B1829 "min idle air" to 63 throughout the table.

Next start by entering 1.10 in b1651 and b1652. This is a good starting point.

B1844 and B1845 set to zero throughout the whole tables and save(please keep a copy of your current tune to keep these values we need them later)

Run standard timing corrections and keep spark to around 15 degrees for testing at idle.


Start the engine(warm up) and log timing and airflow, remember these work together. Please use STFT's aswell as it will trim fuel as idle vacuum improves.

If timing is being corrected to low ie around 5 degrees. We know that max idle air is to high, it needs to be deccreased. Also turn on a/c and watch the timing it will increase a few degrees. If the car is an auto put in in "D" and watch the timing figures. If timing is to high decrease (should this read "Increase" ) just checking :) ???
max idle air by 0.04 at a time. change by 0.02 when close.

Step 3.

Adjust max idle air up or down to get desired idle and timing. In a manual I would go for around 15 deg idle a/c off and 18-20 a/c on. Auto pretty much the same but in D maybe let it creep into the 20s.

Now we have that right time to get min idle air correct. Min idle air is actually desired airflow. Also it is overdone in factory trim and works well for a stock cam but it needs to be simplified to make the car run smoother and prevent hunting. Once its correct it can be massaged.

Populate the integral and proportional tables I mentioned earlier. In the past I spent much time on these when I realised that its not overly important. To get simple effective results min idle air and max idle air and timing are most important. All that is required is to reduce these values by say 50%. I go into integral and reduce by 50% same as proportional. Even 20% is enough in both. In fact plenty as long as the 4mm bypass hole has been drilled its fine. Ensure these are populated and save the tune.

If min idle air is to high the idle becomes "maxxed out" as I call it meaning that it is set higher then max idle air. eg 10 g/s could equal 1.10 max idle area this isnt always the case but in general its close.

Set the whole table to 14g/s. Yes the whole min idle air table. Start the engine and while logging etctp watch what it says. Please note this is the main value you check while adjusting max idle area and min idle air.

Once the engine is running take note of the TP%. Rev the engine let it settle to idle and see how long it takes for the TP to start trimming. If min idle air is to high it will take 10-15 seconds before TP reduces from the max idle area position and starts to trim. If its to low and min idle air needs to increase. It will trim immediately if it is low. We increase until it begins to max out then we keep those values. Again, when there is a delay in trimming by 10 or more seconds we know it is maxxed out. Experiment with 14 s a starter and likely you will need to reduce some calibrations are different, Generally 8g/s is where it ends up.

Now to finish off the min idle air. Again, this table is overdone. When infact all gears including N and D can be all the same. The table should minorly taper upwards towards higher rpm. Remember as soon as the values are above max idle area ie(what we checked for before) this is the value that the figures are maxxed out and overlooked. So anything over say 12 is a waste of time as its not even used. Not even the GM engineers sat down to work this one out.

So set upto 1000rpm your final value of min idle air that you worked out. ie could be 8g/s. from 1000-1200 go 9 1600 up 10 and 2000 up 12. Again leave all the gears and P N etc the same value. This is ALL that is required here. Keep it simple like this to avoid hunting or overcorrection.

Step 4.

We have established correct desired airflow by using our max idle area to find it. Now we have it right we can slightly increase max idle area. This allows the pcm to learn and trim within a fine limit and allows perfection of idle in all conditions cold and hot start, winter and summer, Also full lock, with a/c on in gear and nice throttle feel with no surging or overshoot.

I have found over time by tuning a variety of e38 combos from blown to 240s cams on tight lsa to baby cams that an extra 4% add on is sufficient.

So if we first found max idle area for correct idle was 1.10 , our final figure will be 1.14.

This allows more more air at cold start, The factory pcm adjustment will increase min idle air at cold ect by a multiplier. But we need to ensure that we have enough min idle air at cold start to get a nice idle cold. Cold start enrichment here is very important but that's another topic.

Add 0.04 to the figure, If it is not enough add 0.02 more. But generally 0.04 is enough with good enriched afrs cold off 13:1.

This will get your idle correct. Small changes will be required depending on combo and pcm cal. But overall there all similiar outcomes. Max idle area and min idle area always vary from car to car hence why its so important to do a custom tune on each vehicle.

If you are having troubles idle tuning, this will fix the issues. So many tuners believe min idle air solves everything but it doesn't and those cars tuned like that show it because they surge or hunt slightly which is annoying. Some e38s will get the idle right straight up without these procedures but overtime with increased cam overlap mostly the idle has a LTIT effect that learns upwards which is a bad thing. The e38 has outstanding control. Why not use it and get it idling better then that small block? My 240-242-111 now idles like a 220s cam in a LS1 so give these a try and you maybe want to try that bigger cam. Please feel free to pm me on any of this stuff.

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Originally Posted by The Alchemist

See query below...great explanation helps a lot !!!

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There is a bit more work in auto's, If timing is to high and the engine is lagging below commanded idle rpm it is because airflow is to low. In drive in autos, generally the engine needs more airflow as it is pushing on the convertor. This can be done though the min idle airflow tables once you have a desired idle airflow established, which with e38s is very sensitive, 1 to 2 g/s out and they overshoot. I am adding some more info on cold start tonight. What I have found though is that it is very simple to obtain a decent idle with little time spent, And once the correct min idle airflow is obtained max idle area can be returned to factory values. I will go over the cold start info in detail and hopefully help out some people who have asked questions on this and run into problems. Basically the engine should start dead cold with minimum time required for warm up before the car can be driven away with no sluggish or surging behaviour.