Occasional rough idle?
 

Hi everyone,

I'm having a little problem here and need to know if anyone else is having it as well. My MS is fully tuned, fuel and spark, and strictly speaking runs great.

Except for this one issue: When the coolant is warmer than 50C (122F), the idle sometimes feels a little rough, like a cylinder is randomly misfiring once every one or two seconds. If the MS is also controlling the ignition, the revs will bounce back and forth from 600 to 1200rpm, like I have lumpy cams installed

By "sometimes", I mean that I may start the car, warm it up and it runs great until I switch it off and restart. Then it may (or may not) exhibit the problem. It is mostly an on-off problem. It will either exist from start to finish, or not at all.

If you gentlemen could be so kind as to say "Yes, I think I have it." or "No, I have experienced anything like it." then I woul be most grateful. I need to know if I am the only unlucky bloke, otherwise maybe I can talk James and the other good MSnSe developers into having a look.

I have a complete description in the MS-extra forums, other setups seems to have it as well: http://www.msextra.com/viewtopic.php?t=22625

Thanks,
Jim

It happens to me every once in a while also. I've tuned most of it out by slightly modifying both my warmup enrichments, and the ve table. I doubt I'll ever get it completely ironed out but now when it does it it only fluctuates between 700-900. I don't think my tables would be of much use to you though since I have a 1.6L, and I had to modify my values from the 1.6L base settings from other 1.6L .msq's.

Brian

The key symptom is that it randomly appears and disappears (completely) as you switch off the engine and restart it. It may be warmed up all the way and running fine, you switch it off and restart, it idles badly. Switch it off again and restart, it runs fine. Repeat as many times with randomly selected bahaviour when restarted (idle fine, idles roughly).

my car does something like this. it'll idle really rough randomly. it doesn't dip below an indicated 700 rpm or above 1k ever, but it IS inconsistent.

and it's running on the stock ECU.

and I've cleaned out my intake manifold.

do you use the stock IAC? what about VTCS?

It's not doing it with the stock ECU (I can switch the injectors back to the stock ECU one by one). The IAC and everything else is still handled by the stock ECU.

Reverant, I get the exact same symptoms on my MS'd Roadster.

I also get the ignition spikes that Foundsoul gets and mentions on MSExtra

Richy, I get the ignition spikes as well. Not good. I think we need to "escalate" the importance of these issues in msextra.com...

I don't get that problem.

On real cold starts, the engine will sometimes die or idle really low (400rpm), but a little tap of the gas wakes it up.

Al, which version do you run? MSnSe (029q2, 029t), HR...?

Yeah I've been meaning to post to add an extra voice, it doesn't worry me *too* much atm as I'm n/a but I will have a supercharger in a month or two and I don't want to grenade my engine :(

I'm also N/A at the moment, that doesn't make me any less concerned, there aren't only spikes "out there" but dips as well, you can feel them pretty hard when starting from a red light on an upward slope, you feel the engine bogging down as if you instantly lifted your foot off the throttle. Very irritating and bad for the drivetrain as well.

Anyone else? Yes or no...?

29q2

After looking back at some datalogs, I realized I have this problem also. Ignition timing dips to 13 when 22 is called for, and the idle varies. It took me a while to realize that it isn't always there, and that it's all or nothing. Either it runs great, or it has both problems. I'm updating the code today which should solve the timing issue.

Mschlang,

check your PMs at msextra.com. Thanks,

Jim

I'm having the same problem. I'm still at a very rough tune, though. Anyone tried a different trigger predictor algorithm?

Arga,

you have this issue on the MS2/extra?

Jim

Just Bruce&Al code v2.8. Yes, same problem.

I was thinking about it and if spark control is causing this then either
a) The dwell is toggling between values
b) Spark advance is fluctuating
c) The timing base is fluctuating

I'd guess 'b' is the most likely. My advance table is evenly distributed across the rpm band and the biggest deltas are at low rpms. It might be worth it to move some of the bins at higher rpms down around 1k rpm for better resolution at idle.

I pulled my wiring harness out last night for modification so it will be a few days before I can try anything.

Can one of you post a data log of this sort of event? *EDIT never mind... saw it in your msextra post

One thing to remember is that the EGO sensor senses oxygen in the exhaust. If it's reading very lean that can mean a misfire (extra unburnt oxygen), not necessarily that it's getting too little fuel. There were some posts in the msextra forum which seem to forget this little fact. So basically you can ignore to O2 sensor when the car is misfiring, it's meaningless.

Anyone "new" to the Megasquirt scene having this problem as well?