bouncy idle

tmbg · Post by **tmbg** » Mon Jun 05, 2006 8:46 pm

Hi folks,

running MS2 2.36, v3 board, MT 2.25, '88 300ZX turbo.

Can't get it to idle stably, it was idling real rough and low at first, I adjusted the idle stop screw to try to get it to idle higher, now it bounces back and forth between 1300rpm and 400rpm.

I've tried to tune for minimum MAP, but with it as unstable as it is, it's very difficult, and tends to stall out. It smells very rich, rich enough to make my eyes water, and O2 goes from 1V to 0.3V, back and forth, which makes me think maybe it's misfiring, but if I lean out the idle bins, it won't stay running.

For cold idle I'm using the stock bosch AAR, no computer control.

Please let me know if you have any thoughts, tomorrow night I'll try to actually get a datalog posted.

Thanks,
Ian

tmbg · Post by **tmbg** » Mon Jun 05, 2006 9:20 pm

ok, so I couldn't resist, here's a datalog...

I think my neighbors probably hate me... it's 1am and I'm in the garage running my Z. It's not the quietest beast in the world either, with its 3" straight through no-cat exhaust :/

MegaScott · Post by **MegaScott** » Tue Jun 06, 2006 12:22 am

Sounds like you have the EGO minimum RPM limit set too low, you have a NB sensor? You will get hunting with the EGO correction kicking in at idle, raise the limit and re-adjust the idle VE bins for a smooth idle.

tmbg · Post by **tmbg** » Tue Jun 06, 2006 4:54 am

the EGO minimum was 1300, I turned it up to 2000rpm, now it doesn't hunt way up to 1700rpm...

now it's like it idles great at 850-900rpm for a few seconds, then falls off and either dies or races for a second to get back to idle. Similar to what it was doing before, but not as cyclical.

MegaScott · Post by **MegaScott** » Tue Jun 06, 2006 6:06 am

What is your configuration? (msq) do you have high or low impedence injectors? what VE do you have at idle?

From the looks of your datalog I think you have plenty of cranking enrichment, you might need to richen up your VE, your after start enrichment looks so so, your Warmup enrichment looks like it needs some richening up. Standard tuning stuff on a first run situation.

See - http://www.megamanual.com/v22manual/mtune.htm#howto

tmbg · Post by **tmbg** » Tue Jun 06, 2006 6:14 am

they're high impedance injectors, 260cc on a 3000cc engine, REQ_FUEL is set to 12.9, idle VEs are around 25.

It seems like it's running very rich, but I'll try playing with the ASE and WUE.

I guess I need to go get that LC1 I've been wanting.

mops · Post by **mops** » Tue Jun 06, 2006 12:38 pm

I have basically the same problem. I.e I'm having difficulties tuning idle.

here's what I tried and my observations.
I have PWM idle valve, so I can precisely adjust amout of air with MS. I my car idles great at 1000rpm, but stock idle is 800rpm.

To achieve 800 rpm idle I have to reduce amout of idle air or reduce idle timing (currently 12*BTDC)

Either or combination of those things will get my idle down, BUT then idle is very weak. That means if I rev the engine and then relase the throttle then rpms will drop to below idle - like 600rpm, then recover from there, but it will overshoot idle again, to say 1100rpm, and few more oscillatios like this until it finds the idle. Enriching does not produce stronger idle for me.

I tried enriching and advancing timing below idle point, so it recovers good, but still the actual idle point is weak.

To make idle strong then I have to run, say 14* BTDC idle timing and allow more air in, then idle is much better and stabler. but then it's pretty high, like >1000rpm... leaning out does not work well... it will idle there as lean as 16.something:1 AFR's then then it will start misfiring....

And I cant stabilize idle speed over time... i.e. once I set it up at some point on the next set of lights it can be 50rpm higher or lower than i set it to originally.

I have other areas tuned pretty well by now and car is great to drive, but idle is ALWAYS bad.

arnold · Post by **arnold** » Tue Jun 06, 2006 1:13 pm

I must admit I am in the same trouble: car drives pretty well, idle is bad. I can get the idle right, but when I rev it and take my foot off the acceelarator the engine dies or almost dies
Maybe the supercharger and bypass valve makes it even more complex. I use the Bosch aux. air valve for cold starts

tmbg · Post by **tmbg** » Tue Jun 06, 2006 1:19 pm

mine actually dies when you hit the throttle at idle... it takes a lot of finesse and a very light touch to rev it up. I'm guessing my problems are mostly enrichment issues...

I'll screw around with it some more tonight. I haven't gotten beyond idle yet, so I dunno how it runs in the rest of the map!

mops · Post by **mops** » Tue Jun 06, 2006 1:40 pm

tmbg wrote:mine actually dies when you hit the throttle at idle... it takes a lot of finesse and a very light touch to rev it up. I'm guessing my problems are mostly enrichment issues...

I'll screw around with it some more tonight. I haven't gotten beyond idle yet, so I dunno how it runs in the rest of the map!

try running bit more timing at idle and at idle rpm, abouve idle load - it will make off idle response much better - but will not fix all your tuning issues.

my idle is bad, and my cold idle/warmup idle is really bad, with engine looping, bucking, idling at 2krpm and then 700 rpm, bucking some more...

most aftermarket ECU run some sort of idle control algorithm, it would be very easy to write one up, i might actually have a go on on it.