Stumbling idle on cold start.
 

First off, on cold start what AF are you guys idling at and on what injectors?

The weather has just gotten colder and on a cold start my car has a stumbling idle for the first like 5 minutes of the warmup. It tries to hold 1500 rpm, but stumbles repeatedly. After 5 minutes, smooth as butter. When the weather was warmer, this was never a problem.

My AF is like 13.1 when warming up, maybe a bit leaner. Could a lean warm-up enrichment be the culprit?

You gotta run your shit rich when it's cold. Fuel doesn't like to vaporize when it's cold. I run 10.5-11:1 until coolant is 100*C. And I complain cause mine doesn't idle dead smooth at 700RPMs at 30*C and I have to idle the damn thing up to 1K to get it to smooth out....

I had no idea it had to be that rich. I will change the settings and post back.

Also, running less timing and more throttle helps smooth out idle. But I hate engines that run like that. I like them advanced and throttled back. Makes them quieter at idle, but it ain't as smooth when cold. IE-my shit would idle at 700 at 30*C smoothly if I'd back the timing to 10* and adjust the throttle to reset the RPMs.

100*C? Doesn't warmup stop at 160*F? 100*C is over 200*F. Did you mean *F?

Define "cold" :D

I idle in the high 14s when warm, usually mid to low 13s when cold. (Cold in CA and FL being defined as < 70°F.) Injectors are 440cc.

I idle at about 1,200 RPM when cold. I think my ignition advance in that region is somewhere around 16°. And yes, it's a tad lumpy. Not "OMG, it's going to stall" lumpy, just "Hmmm- that car sounds like it needs a tune-up" lumpy.

More warmup fuel is certainly something to try, especially if you've not tuned warmup down in the temperature regions you're currently experiencing.

My cold start AF is quite fat at around 11.5-12 at 1200 RPM when ambient is <50F. It doesn't stumble per se, it just sounds like a cold engine. Once coolant is up to 100F, idle gradually reduces and AF gradually leans. Running 10g with 460cc. Warm idle is smooth at 14.5 AF and 1,000RPM. Suppose I could run a slower idle but it would certainly need to be richer to keep it smooth.

Yeah, all temperatures should have been in Fahrenheit, not Celsius. And I'll also add that idling 10.5-11:1 is not typical. But my engine likes fuel.

needs more return line.

+1

I warmup no richer then 12:1. Does great.

Thanks for the tips guys, this timing stuff is confusing.

Yes it is. I idle ~20*BTDC. I let it warm up and then set my idle to ~700RPMs. So quiet you seriously can NOT hear the engine running. You can feel it a little, but can't hear it. Reminds me of sitting in a camry.

But the idle is very "weak" cause the engine is barely using any air/fuel at all. So initial tip in sucks. IE-if I stomp the pedal, it has a delay/hickup before it revs up. But I like it idling this way.

If I were to put my timing back to 10*BTDC, the engine wouldn't even idle because it would slow down and not spin fast enough to run smoothly. So I'd have to compensate by adjusting the idle at the TB to get it back up. The net result is the same RPM, but now the engine is pumping more air/fuel through it. It's easier to light more air/fuel. Plus it's easier to maintain target A/F ratios when your moving more air/fuel.

Only thing that sucks is that if I idle at 700 it doesn't do good when I turn on the A/C. I either gotta retard timing some and idle it back up a bit, or, hook up a fast idle valve to automatically idle the engine up some.

I think im gonna need a flash animation to understand this.

More timing = less air\fuel used = less throttle adjust?

Less timing = more air\fuel used = more throttle adjust?

More timing idles worse when cold, less timing idles better.

Just break it down for me.

I thought I did break it down...

I'll try again I guess.

You add timing, the engine speeds up. ( to a point of course, you can't add a million degrees of timing)

You open up the throttle by adjusting the little set screw and the engine speeds up.

You retard timing and the engine slows down.

You close the throttle by adjusting the little set screw and the engine slows down.

So you got two ways to play with idle. Timing and throttle. And fuel is a third, but it makes much smaller differences.

If you want a smooth, strong idle, and great tip in (what 99% of normal people want), then keep base timing conservative (like 10* or something) and then adjust throttle to get RPMs where you want.

If you want a quiet idle, not as smooth, shitty ass weak engine that bogs when you turn on the headlights and dies when you turn on A/C, then advance the timing a lot and back off the throttle. That's the way mine is. It uses a bit less fuel at idle, sounds different (better IMO), and quieter.

Awesome, thank you.

Last night I backed off my timing a bit, and richened up the warmup and it was night and day.

Why is the tip in better when the timing is around 10* vs 18*?

and.

Why is the engine stronger when the timing is retarded to 10* vs 18*?

The assumption with either of these is that you have the same RPM and AFR at idle. IE-say you have two identical engines at an 800 RPM idle. Only difference is one is idling at 10* BTDC and the other at 18* BTDC. The one that is at 18* will have the throttle adjusted to be less open than the engine at 10*. This is because the motor running 18* is more efficient and, given the same air/fuel as the 10*motor, it would idle much higher. So you have to choke the engine back a bit more to get it to idle at the same RPM.

Difference of course is one engine is pumping more air/fuel through it. That would be the 10* motor. This makes it more stable and generally smoother. It's not really "stronger" as it's actually less efficient. But if you try to idle away from a red light without applying throttle, the 10* motor (the one that has the throttle opened more) will make more power and not stumble or hickup as much as the other engine.

I dunno what else to tell ya. The lowest cell in my timing map right now is 20*. Fired it up this morning. It was 33*F out. Idled at 800 smooth as could be from a cold start. At 20* BTDC. Amazing what you can do at 10.5:1 AFR's. ;)

It seems you arent the only one that believes in a lot of advance for idle. I have spark tables of about 15 people, and the majority idle at more then 15.

Can you do me a favor and post your warm up enrichment table please.

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Why is your fuel VE Table and your AFR Targets table 15 x 15?

Also, where are you finding that Warmup Curve editor?

Your percentages for the warmup are also really small, mine are ridiculous right now to get down to 11:1

The accel wizard numbers are also much much higher then what I have.

The ve table is 16x16. The Spark and AFR tables are 12x12. None are 15x15...

I go into megatune and click "startup/idle" and then click warm up enrichment.

Probably cause you don't idle at 11:1 when it's warmed up.

Also, I'm MS2E, hence why my ve table is big and the software is different.
And I have a different engine than you, so that's probably why my settings are different. ;)

^ You gotta tell me these things man. Im like "woh" over here. But that was my next guess.


I really need to sort this shit out, I gotta try and switch the timing from 17 to 10 and see which idles better when cold.


Will post back with results, thanks for nursing me through this. I really appreciate the time.

This is weird as hell.

The winter before the turbo with megasquirt, idling in freezing temps was dead stable. Since then I have not touched my warmup enrichments, or idle timing. Soon as the temps dropped, I started having these weird issues. My warmup bin at 140 is like 150%, and its getting me to 12:1 maybe. Really horrendous idle, as it gets warmer it gets better. Once passed 160* its totally fine.

I have two theories now.

Either its a weak spark. My thoughts are if it was weak then id probably have problems at WOT at 14psi. Id imagine weak spark at idle would be even more prevalent under load.

TOO much fuel during warmup, The car reaks of unburned gasoline when it sits their warming up, like really nasty. Im thinking of chopping the WE back to what they were and starting again.

This is COP setup too. Running a 4ms dwell for crank and run, because any lower and the car doesn't start. So I have been running 4ms ever since installed them with a .5ms discharge.

Could the spark plugs be due for a change? I think, again, it would be more evident under load.

Its pretty freaky, it idles but its just all over the fucking place.

Also, I haven't yet experimented thoroughly, but it seems the car warms up more steadily with the headlights on? No definitive tests yet, so its a big MAYBE on this point.

So I was just doing some serious brain storming.

My car idles great when warm, at that point the engine is at 10* of timing because the map has dropped. But when its cold started, its warming up with almost 16* because the cell above the 10* is 18*. So its scaling somewhere in there.

Would lowering timing to 10* during warmup help with idle quality?
Is there anyway to pull timing based on engine temp?

I am going to try this tonight but id like to hear some thoughts.

Usually, you would add spark advance when the engine is cold. You can adjust timing based on temperature from the Spark -> IAT / Clt Related Ignition screen.

Sam..... I don't know what to tell you. Post your msq and I'll look at it.

Oh yeah. Fired up my car at 31*F a couple days ago. Purs at 800 now. Dead smooth and very strong. No hickups or nothing. Sounds like it's completely warmed up. I mean so smooth, it's scary.

Ill have to take you up on that, I really dont know what else to try. Ill post it tomorrow, I left the laptop in the car.


What I know now for a fact, after exactly 140F the idle becomes dead stable.

Retarding the timing to 10* did help make it a little better when starting totally cold.

Can you explain the logic behind that please?

OK. So i definitely get an improvement idling closer to 20* when cold. A very big improvement in fact. I left it there for now, and I decreased my idle rpm with the idle screw once it was warm. Tomorrow ill see what happens from a full cold start.

Ok. Seriously.

Why are my warmup bins so god damn high. 150% in the 140* temp.

Could this be the sign of a failing fuel pump? I have never had to have them so high.

My AIT correction for heat soak are also ridiculous and almost have no effect.

+1

Please take a look and tell me what you think.

Any ideas Pat?

I'm gonna say you are probably having an ignition problem. I see you're running a lot of dwell, and I remember reading before you had a miss when running "normal" values for dwell. I suspect this is your problem. How much gap are you running on the plugs? Try gapping them to .020".

The car would not run with values of 3.5/2.5 when I first put in the COP's. Ran spot on with 4.5/4.5 which was what I ran for factory coils. It also ran like this, spot on, through last winter, which was pre turbo.

I also am running the stock gap.

Ill play around with it just a little bit more, but if its truly not solvable im gonna find some new coils. Changing spark gap is not a solution.

Run .020" to see if it has an affect. IE-we're trying to diagnose the real problem. So do it anyways to see if perhaps this is an ignition related problem It won't cost you anything but 5 minutes time. And what's it gonna hurt to run less gap anyways?

If it doesnt hurt to run less gap then why did everyone jump on the bandwagon to go to COP's to run a bigger gap?

Ill try it, and report back.

Same reason everyone buys a dual feed fuel rail.

lol, except the dual feed rail was proved useless. While it was proven that the COP's provide stronger spark then the factory coils.

If I find some plug wires this weekend, ill connect my old coils and see what happens.

Better. question. How often should plugs be replaced since the engine is now turbocharged?

I haven't replaced mine in 4k miles since I went turbo. Running regular coppers.