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Wild idle fluctuations when below 1300 rpm

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Finished building up a 3S-GTE engine for an MR2 but could not get it to idle properly below 1300rpm. Anything lower would gradually cause the rpm to fluctuate more and more the more I close up the ISC valve or idle adjustment screw and would eventually fluctuates to a stall. ISC is on open loop and I have went as far as plugging the ISC port up to control idle with the adjustment screw only so it is not the ISC settings that are causing the fluctuations.

Aftermarket cams were installed on the car and degreed per manufacturer spec while building up the engine. These were Kelford 264 cams which isn't that aggressive. However, the final adjustment on the cam gears were a little worrisome as the adjustment were pretty must at the end of the adjustment scale on the exhaust gear with 11 degrees of retard but I did measure it two more times while building up the engine to make sure it is correct. I know aggressive cams will require a higher idle due to note being able to pull sufficient vacuum but 262 cams are far from aggressive and looking at my MAP readout, vacuum is pulling strong. I have another 3S-GTE engine with the same cam that idles just fine at 900 to 1000 rpm.

Lambda looked stable enough to me and would be fine tuned once the idle problem is solved and I have already flattened the ignition map a little to make sure its fluctuation between the rpms isn't causing the problem.

Right now, I am truly stuck on what's causing the crazy fluctuations in rpm and cannot progress any further with the tune.

Attached is the latest map used and a log from startup where the rpm was stable and high until the engine warmed and the ISC valve started closing up and the fluctuations begins. Manually pushing the ISC% back up rises and stabilises the rpm.

ECU map.pclr ECU log.llg

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I'd start by flattening out the ignition map from 1500rpm and below to a much lower value so the engine doesn't make as much torque, try somewhere between 10-15deg as a test.  While working through what ignition works best I'd also target something like 0.9 lambda

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Agree with JMP here, less advance (flat all the way to 1500) and set it richer initially.  Once you get the ignition right you may be able to lean it back off but its easier to start on the rich side.

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Thank you for all the feed back.

Yep, seems like my attempts to "flatten" the base map had gone the completely opposite direction. Instead of lowering the ignition for 1500 rpm, I raised ignition for the lower rpm range to match with the higher rpm and made the matter worse.

Following the suggestions here, I started the up the engine with around 15 degrees ignition across the board. It still fluctuated initially but after further flattening everything to 10 degrees (map1 attached), the idle stablised significantly (the last section in log1 attached).

However, after shutting down and restarting the engine, the revs started bouncing again. After playing around with the ISC% and igniton timing again, idle seems to have settled down a little with ignition lowered all the way to around 7 degrees (map2 and log2). Also, after blipping the throttle, it takes awhile for the engine rpm to settle. Regardless, things seems to be on the right track and it probably just need more work from my end to make it better but I was already choking to death from the exhaust and had to call it a day. No exhaust was installed yet after the downpipe and I was standing right next to the engine (and down pipe) while updating the map breathing in all the exhaust.

map1 https://drive.google.com/open?id=1IaVah5A4vdlLyH5JfTU0La5ZAXwTz1y4

log1 https://drive.google.com/open?id=1F5teTRz1bkeCcFuiAugsOg4vFyMkF3JF

map2 https://drive.google.com/open?id=1GJgUpzr4-_9pc9KzLwfxF7Bis5nZ9MTm

log2 https://drive.google.com/open?id=1EdA81ldKOtN2gkaN2j2tRC-8LZXLyyAn

 

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So the point in your log where idle is stable shows ~5 deg of timing. technically you could just set everything in the ign1 table below ~1500rpm to 5deg and it should stablise. This is quite a low number though so I suggest you set everything below 1500rpm to say 10 or 15 deg as suggested by JMP, but it must be all the same number in the cells near idle (for now). Once idle is stable, even if its too high, you can proceed. Next thing is drop the values in the base idle table a few points until you get the idle rpm you want. 

Once you have it mostly stable, turn on ignition idle control, with the "zero error" cell in the middle set to the same 10-15 value you used in your ign1 table.

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Finally got some time to work on the tune again. Managed to get the idle to be somewhat stable with 10 degree ignition and enabled idle ignition to further dial in the idle. As I was dialing in the idle ignition, it still felt like things would benefit with a slower igniton with 8.5 degree in the zero error cell.

Throughout the day, I was struggling hard to keep the RPM with dipping and fluctuating for a few cycles before stablising after blipping the throttle or a warm startup. After spending some time with close loop idle control (which seem to have little effect) and also working on the fuel map, things seem to have improved a little. By the end of the day, the RPM would still dip by roughly 100 rpm and takes maybe 4-5 seconds to stablise again but was already much better than what I started with. There seems to a brief moment where the engine would run lean after lifting off the throttle but I can't seem to tune it out (I've checked and it's not overrun fuel cut). Not sure whether that is the cause of the rpm dip.

Also to note on the A/F ratio is that the 0-5V signal coming from the AEM gauge seem to be a little off. When it's at stoich on the AEM gauge itself, the ECU is reading 1.05 lambda. It is not a grounding issue as the ECU and gauge share the same ground and I have read the voltage right at the connector of the gauge between the 0-5V signal and ground and the voltage given off is indeed slightly different from the calibration table given. It's not a big problem and I would deal with it by adjusting the calibration table later. (Damn, I missed the Link CAN Lambda on my own car).

If I rise the idle RPM to around 1200, things were significantly but my friend (the owner of the car) seems to prefer a lower idle even if it sacrifice power. I am wondering how much cam timing would affect the idle quality. If it would help, I am thinking of advancing the exhaust cam by 2 degrees from its current position if it would help (the intake cams are too difficult to access with the engine still in the car).

 

Attached is the latest map I cam up with so far and a log showing the oscillation on a warm start up and throttle blip.

https://drive.google.com/open?id=1dagL6I2eSxUJwja4YKddCcbGYx1dAw2U

https://drive.google.com/open?id=1pMdI18ZQv1IT4mYq6pBPsVz-qQXhBRWn

A big thank you for all the help I have received here so far!

 

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Its going lean because of this pink area in your fuel table, I suggest copy the cells from the 35kpa row up into the ones I have highlighted in pink.  I would also probably bump the CLL RPM lock out low up to 1500 so it is not turning on & off right around idle.

ww0ffuX.png

 

I think I would also change the idle ignition table to something more like this:

2Prj827.png

 

 

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