I've done some searching around and didn't find much on the topic but I have the feeling this is pretty common knowledge and pretty commonly stumps early tuners.

What should my timing be at idle? Should I tune for best vacuum? Tune for smooth idle?

My situation:
Car will idle at a good AFR if my timing is at like 7-10. But -17 or -18 on vac.

With 18-20 degrees at idle I get great vac at -20. But idle will hunt around unless i throw fuel to the point where the AFR's read 11-12.

I only have 440cc RC injectors.. idle shouldn't be an issue. Any other factors coming into play here? My startup is also crazy.. Shoots my RPM to like 4 grand after startup and then settles at an idle. Let me know if any more info will help you help me.

 

I run 10-12° at 14.7-15:1 AFR

 

Good to know, what injectors? Do you have a good idle?

 

rx7 460s. and yes my idle is great.

what ECU are you using..

 

Spark advance at idle is a lot different than the other spark tuning we do. On my car, I found that I maximized RPM and vacuum with an advance in the low 30s! However, when I did so, it caused the following problems:

1. There was so much advance that I couldn't get my idle speed below about 1200RPM even with the idle air screw closed and idle air control valve at minimum duty cycle.
2. Recovery from low RPM excursions suffered because the BMEP point would radically move towards and even before TDC (exponentially) as the RPM decayed. This is a unique property of the low-RPM idle region.
3. The advanced BMEP point at very low RPM's also made starting difficult, often with kickbacks.

So, tuning advance at idle is a compromise amongst various factors. Unlike most of the map, we're not shooting for an optimum spark advance that maximizes torque. General consensus is that a value between 10° and 15° BTDC seems to be a sweet spot that works well with the stock idle control mechanisms, gives good starting and good low RPM excursion recovery.

I'm running 12° BTDC and kick that up to 20° BTDC when the AC clutch kicks in using the MS spark table switching mechanism. This helps compensate for the drag of the AC compressor. My idle AFRs (after warmup) are ~stoichiometric.

Another thing to consider is what cells are the "idle" cells. In order to cover engine start, you need to set idle timing into your lowest RPM column all the way up to 100kPa. You'll notice before you turn the key that 100kPA and minimum RPM is the cell where you begin.

 

one of these days I'm going to go out and figure out what advance at idle can reduce my pulse widths the lowest and still see stoichometric.

 

I think if you do that, you'll end up at the large advance settings that produced maximum vacuum. As discussed above, those advance settings caused a lot of other problems.

I think you're already in a sweet spot, especially if you're still using the spark table switching for AC. After all, I copied your settings.

 

Great- what are your vacuum readings at idle with 12 degrees? Are you saying the sacrifice I need to make is in vac and idle speed?

On the topic of "Idle" cells, are you suggesting that this is causing my revs to shoot up immediately upon starting? I've attached a log of my startup problem.

 

I see 32kPa at idle...which less [vacuum] than most.


your RPM shooting up is result of some sort of startup setting on whichever ecu you may be using.

 

The ECU is DIYAUTOTUNE - MegaSquirtPNP MM9093

 

I'm at about 18-19 in. Hg. of vacuum at idle. And, yes, you sacrifice maximum torque timing in the idle region because of other considerations.

Your RPM zoom looks like a different problem. I suggest you address basic idle performance first. Here's a procedure that worked really well for me in setting up MSPNP9093 idle:

1. Setup idle VE first. I would recommend shooting for maximum vacuum in setting up idle VE because it is a good, non-noisy signal at idle conditions. It ends up being ~stoichiometric, but it is easier to set than using AFR. Use the following steps:
a. Change Idle Control Algorithm to "PWM" and "Warmup Only." Set your minimum duty cycle to 19 and your "Idle Duty at Upper Temp (DC)" to 19. What we are doing here is eliminating variables and putting the idle air control valve under your direct control.
b. Start the car and let it warm up. You should notice that once the "Slow Idle (Upper) Temp (F)" is reached, your idle duty cycle should be fixed at 19.
c. Now, adjust your idle screw to give you an RPM that will keep the car alive while we mess with idle area VE. 1000RPM should work fine.
d. Now were going to find the best VE for your idle, knowing that all other variables are fixed. Go to your "Fuel VE Table 1" and note your current operating kPa and RPM. We're going to change all of the VE cells surrounding this point so that we get a constant VE without interpolation. In my case, I ended up at a VE of 40. It was a very distinct peak.
e. Once you've found your idle VE, set all of the cells in the idle region to this VE to provide stability for your engine. That would be all cells up to about 35kPa and 1500RPM. Your idle VE should be the minimum VE in your map.

2. Now setup idle timing. Just use something between 10-15 and be done with it. If you want to use spark table switching to stabilize your AC-on idle, then use a lower setting, otherwise just set 15. As with VE, make sure all of your idle cells have the same timing to provide stability to the engine. In addition, adjust the timing in your lowest RPM column to idle timing all the way up to 100kPa to provide constant timing for cranking.

3. With VE and idle timing set, and while still in "Warmup Only" mode, adjust your idle air screw for your target warm idle speed. I adjusted for 900 RPM. The basic idea here is that we are setting the minimum air bleed (consisting of minimum DC + idle air screw). We want the closed loop idle control to be able to add air for loads such as lights, AC, higher outside air temperatures, etc. But we should not be relying on closed loop idle to provide our minimum idle air setting. Note that your idle air screw should be at least a full turn open to avoid large % orifice size changes with metal cooling and heating. If this results in too high of an RPM, then reduce idle timing. You can see how these things are interrelated.

4. With all of the above done, you can now return to "PWM" and "Closed Loop Only" and mess around with closed loop settings to provide recovery from loads. Note that if you don't have big loads like AC, plenty of people are content to just use "Warmup Only." It is simple and stable.

After you get idle stabilized as above, post another recording of your startup RPM zoom.

 

Forgot to ask. Are you still using your MAF?

 

Nope. Removed.

 

Those instructions sound very helpful. Our setup seems pretty similar, what are you using to tune..? I'm debating the switch from Mega Tune to Tuner Studio. I'd like to take a look at your MSQ file if you don't mind. Bryan.Spears@Parrot.com or attach it in a reply.

 

Very nice writeup hornet

My idle control definitely needs some work and I didn't have a clue where to start.

 

This is exactly what I had in mind when I created the post. Good to know it's already working for others.

 

MSQ is attached with a caveat -- areas outside of idle have not been tuned -- they are still at MSPNP base map values. I'm still breaking in my turbo and haven't been to the dyno or done any significant road tuning yet.

I'm still using Mega Tune. But I'll probably switch to Tuner Studio due to its auto-tune functionality -- need to make sure my LC-1 is reliable first -- but that's another story. Most of the power users around here are Tuner Studio types.

Doesn't really matter for tuning idle though. Idle tuning is a manual process.

 

That's impressive... I went to save the file to my desktop and I just so happened to have named mine "Latest" as well. Thank you for your words my friend. As stated, I hope this helps others.

 

is it sad I have no idle how to tune MSI idle settings ...

 

Never mind this- just read your build thread - You are using the LC-1 Hornetball - What Wide Band are you using?