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Old 04-06-2010, 12:39 PM   #1
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Default Bouncing idle, steady IAC duty

Hey guys,

I just finished installing my RX7 550cc injectors. It started right up with no problem, and then within a few seconds I had a bouncing idle. My IACV duty cycle stays constant during all of this. Would a vacuum leak cause a bouncing idle, or would that only create a higher idle? It also behaves in the same way if I hold it at a higher rpm. This happens whether in closed or open loop idle control.

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Old 04-06-2010, 12:41 PM   #2
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What are your timing and fuel settings like in the idle region?
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Old 04-06-2010, 01:08 PM   #3
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This is what I have. Before these injectors I believe idle was around 43-50kpa and did not bounce.

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Old 04-06-2010, 01:09 PM   #4
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Your AFRs look like they're fluctuating from lean to leaner. Try adding more fuel and see if it stabilizes.
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Old 04-06-2010, 01:13 PM   #5
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I'll go and try that.

Why does this happen even at higher rpms? Is this a sign of some other issue?

I also unplugged the IACV while it was bouncing and nothing really changed in terms of the frequency, but the overall RPMs did drop, so it seems to me that the IACV is fairly stable.
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Old 04-06-2010, 01:15 PM   #6
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I also see now that your fuel table makes baby jesus cry. Specifically, the values in the 40 kPa row should not be that much leaner than both the 26 and 53 kPa rows. I would bet that's causing a lot of your idle grief. EDIT: It also happens at higher rpm because your 40 kPa values are also fux0red at 2000 rpm.
Also, you don't need 0 rpm columns for either fuel or spark, but I suppose Adaptronic's tables are so huge that it might not matter.
EDIT EDIT: Your timing is okay but it will help if you make the 500 and 1000 rpm columns have identical values at whatever MAP you idle. Similar deal for fuel. You want very close or identical values in the cells that bracket your typical rpm and MAP at idle. That will keep your fueling and timing consistent and help keep the engine from oscillating.
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Old 04-06-2010, 01:39 PM   #7
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Thanks for all the pointers, it seems to have helped a lot. I still don't know exactly how to tune the fuel area at idle very well, but it is stable now.

If I rev it up and let it spin down it hits some rough stumbles. Do stumbles at idle mean too much or too little fuel?

I can't seem to get it to idle leaner than 13.5 AFR with these injectors. I was good to about 15.8 on the stock ones. Is this due to the minimum on time nature of injectors?

Any fueling/timing theory tips are greatly appreciated.

Lots of man love, David.
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Old 04-07-2010, 12:39 AM   #8
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For reference on my 94 with MegaSquirt I idle about about 13.0-13.5 AFR and that is the only way to get it stable. Jerry at DIY said thats what he has seen on a good number of miatas to get a stable idle.
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