When to use IAT vs CLT initial steps for closed loop idle

5.3LS10 · Post by **5.3LS10** » Sat Oct 01, 2016 7:01 pm

Hey everyone,

As the title says I am curious in what situations or scenarios one option would be better than the other.

Everything I had seen points to use MAT but I had a lot of issues with the vehicle staying running while warming up if I ever touched the throttle and knocked it out of closed loop and I would have to play with the throttle to get it back to closed loop. Then when warm it would hang around 1200-1300.

I switched from MAT to CLT and now I can command the larger value when cold but as soon as the engine gets up to temperature I can command the lower value for the IAC.

I have a cold air intake that is isolated from the engine bay so my MAT readings are usually very close to outside temp.

My combo is in my signature.

Let me know your thoughts and see if maybe I have a bigger issue else where and maybe that is why the MAT setting did not seem to work for me.

Thanks,
Shane

Yves · Post by **Yves** » Mon Oct 03, 2016 1:27 pm

I also use clt. No issues with it. Mat didn't work well either.

nathaninwa · Post by **nathaninwa** » Mon Oct 03, 2016 5:21 pm

I found using mat worked for me after undersranding how the table works. My stuff is turbod so I see large temp swings and needed more air when it was hotter. I also noticed when the seasons changed from summer to winter entering idle was goofy using clt. Now I have a 30* to 150* spread to cover most situations

Post by **muythaibxr** » Tue Oct 04, 2016 3:42 am

Nathan's explanation is why you should use MAT.

Yves · Post by **Yves** » Wed Oct 05, 2016 7:44 am

Really ?

What's the reason for a bad idle at cold temps ?
Increased resistance to engine turning due to thick oil, bad mixing of the fuel with air due to low temps and finally increased piston clearance due to low expansion of the pistons since they are not hot (less air entering, less dynamic compression). All of which reduce engine speed.

The first thing is mainly due to engine temp of which coolant temp is a good indicator.
The third equally is dependant on CLT.
Only fuel vaporization is dependant on air temp and CLT.

If air temp is such a good indicator, then tell me why you would have a WUE graph where enrichment is in relation to CLT...

pit_celica · Post by **pit_celica** » Wed Oct 05, 2016 9:48 am

For idle control, you need to control the air mass entering the engine precisely. Air mass vary a lot with air temperature. Engine coolant temp is the same on a hot engine, regardless of the outside temp. At colder temp, air is denser and less air volume is needed for the same idle RPM target. So, the initial duty value for the idle control will also need to be different. This is why you want initial duty vs IAT and not vs CLT.

Your comparison with WUE (fuel vs CLT) is irrelevant because the idle RPM speed isn't really controlled by fuel volume, but rather by air volume.

Sam

Post by **jsmcortina** » Wed Oct 05, 2016 10:06 am

Ken and I have talked about removing the CLT option to prevent the confusion.

James

Yves · Post by **Yves** » Wed Oct 05, 2016 10:22 am

pit_celica wrote:For idle control, you need to control the air mass entering the engine precisely. Air mass vary a lot with air temperature. Engine coolant temp is the same on a hot engine, regardless of the outside temp. At colder temp, air is denser and less air volume is needed for the same idle RPM target. So, the initial duty value for the idle control will also need to be different. This is why you want initial duty vs IAT and not vs CLT.

Your comparison with WUE (fuel vs CLT) is irrelevant because the idle RPM speed isn't really controlled by fuel volume, but rather by air volume.

Sam

Did you actually read what I wrote ?

On my engine I found that the engine always returns to the same idle stepper position no matter how hot the outside temp is. Besides you compensate for air temp already in the fueling calculation.

Yves · Post by **Yves** » Wed Oct 05, 2016 10:23 am

jsmcortina wrote:Ken and I have talked about removing the CLT option to prevent the confusion.

James

Apparently for some people the IAT initial value hasn't worked and you want to remove the CLT ?

pit_celica · Post by **pit_celica** » Wed Oct 05, 2016 2:27 pm

I think that this would be a good subject for a poll on the forum to see what people are actually using (IAT or CLT).

Sam

nathaninwa · Post by **nathaninwa** » Wed Oct 05, 2016 6:56 pm

The trick to iat is paying attention to the current MAT. I was against it in the beginning till I actually tried tuning it and found the idle stumble I was complaint about after a boosted run was able to get tuned out where before just a cruise decel resulted in a smooth idle transition.

Then, though it wasn't bad, I was able to tune those 25* degree mornings into good idle transion where leaving it as coolant I was chasing my tale when the afternoons would be 50 to 60*

It takes bit longer but makes for a well rounded tune.

The mat correction table only does fuel, sometimes we need better initial values to jump start a smooth idle transion

My turbo car application would see 25 to 30* mornings and from time to time would see 120* boosted temps with a coughing idle transion when I was just coolant based

Yves · Post by **Yves** » Wed Oct 05, 2016 11:28 pm

Maybe there is a difference between turboed and NA

And then some

krisr · Post by **krisr** » Thu Oct 06, 2016 4:55 am

With my NA Pontiac I use IAT for my initial step table. I figure since CLT will dictate where the idle speed is and air mass is largely governed by air temps so it makes more sense to give it the correct amount of air volume before returning to idle to prevent stalling or hanging as I can see a difference in steps needed between seasons.. That being said, I've had no issues using CLT or IAT to tune the table, but IAT gives that extra dimension for precision IMO.

Kris

nathaninwa · Post by **nathaninwa** » Thu Oct 06, 2016 6:41 am

Turbo cars see more temp change on a daily basis, where all motor cars see more seasonal changes, but it's not uncommon to see 120* while in traffic on a hot summer day, then see 30* temps while traveling to grandmas house over the holidays

5.3LS10 · Post by **5.3LS10** » Thu Oct 06, 2016 8:43 am

Thanks for all the information everyone.

Sorry I have been tied up on other projects and have forgotten to check back in.

I am going to start by changing back to coolant and fine tune my X and Y ranges to hopefully give me better control.

One thing I noticed on mine (I can provide a datalog to confirm) is that when warming up it requires a much larger stepper position than when warm. If I am remembering correctly almost double.

This could possibly be due to other issues with the tune that I have not sorted out 100% yet. Maybe too much WUE?

I will play with it this weekend when I have some more time.

Thanks again,
Shane

Post by **muythaibxr** » Fri Oct 07, 2016 4:00 am

The closed loop target table gives the sets the target based on CLT, and should be higher on a colder engine. That target feeds into the initial value table, where if you use CLT, you are reusing something you have already factored in on the target table. Instead if you use MAT you get an extra dimension to tune and can tune out stalls and stumbles that occur due to high air temp requiring more air to keep the same idle speed. On my NA engine, this was needed because I have open ITBs and the engine bay gets very hot. I have tuned every car I have used CL idle on this way.

Nathan has it right.

ashford · Post by **ashford** » Fri Oct 07, 2016 8:58 am

the only acceptable way of getting rid of clt based for me would be to include and adder based on coolant. reusing the open loop warmup graph should be doable for that

Post by **muythaibxr** » Fri Oct 07, 2016 4:00 pm

Have you attempted to tune based on MAT?

5.3LS10 · Post by **5.3LS10** » Mon Oct 10, 2016 7:10 am

Well I spent some time this weekend changing my car over to MAT for initial steps and it works better than before. As the days get colder I will keep playing with it to make sure I have accounted for the colder temperatures.

(Colder air requires less air volume so less IAC steps and warmer air will require more IAC steps right?)

Just making sure I understand it correctly. to start estimating the other fields

thanks again for all the help everyone!
Shane

jesse408 · Post by **jesse408** » Thu Oct 13, 2016 5:47 pm

Can someone with experience please post a screen shot of a properly tuned Initial Values Table based on MAT so that we can get an understanding of how the progression of numbers in the table should appear.
When the throttle is lifted, the idle valve seems to go straight to the highest value in any given MAT temp row regardless of RPM. Should the values be lower at lower RPM and higher at hoghr RPM?
If you idle at say 875 RPM should there be a break point below idle RPM? Should that value be higher that idle bin in order to deter stalling, etc?
Thanks.

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