And here I thought this was lonely problem that just I was experiencing. I've gotten so used to it I've all but given up on solving it and just called it another evo quirk. Having multiple projects is a luxury but has certainly lead to neglect of evo, which used to run perfect, now it just runs lol.

I've had this problem for about 4 years. Through 2 or 3 different tunes from 2 different tuners. The latest was someone who spent a lot of time on fuel trims and idle. The problem still persists. Only occurs on warm starts, idle will drop to 500 or a little below, very lean. It never stalls out but certainly comes close. It will either straighten itself out within 5 seconds or a quick throttle blip will fix it and then idle is normal. Idle will occasionally dip and go lean while driving...like you said, if you drop into neutral while coasting to stop or something like that. Again, throttle blip will return idle and afr to normal.

My issue isn't severe enough that I'm going digging underhood to solve it, but as with all issues, its not going to fix itself and its only going to get worse. My searching has lead me to suspect the IACV. Came across a very similar scenario on a 3000gt forum...problem was pretty widespread over there and faulty IACV was often the culprit. You can find youtube videos showing how to test functionality of iacv. Has to do with the faulty valve allowing air to pass during cold start but not during warm start. It's been a while since I read about it so my theory is rusty, but its something you could add to your list of things to rule out. Since you're willing to do the leg work on this one, please update here...Seems like more people than I thought have the problem. I'd really love to see what you come up with. GL

Edit.....Great. After that rant I see you replaced the IAC motor. Well its good to know that's not the problem. The injector leak is an interesting theory. I have RC 750s that are ancient. Still interested in what you come up with even though I've contributed nothing to your search...

 

^ yup that's my startup. But a blip doesn't really help. Holding the pedal does. And takes about 20sec. But super lean. Don't know how opening the throttle helps. That's counterintuitive.

 

I think that's why we're leaning toward a fueling issue. For some reason fuel isn't immediately available so a throttle blip or hold forces it. I remember someone's theory that engine bay heat was causing fuel to vaporize in the rail making no fuel available on startup. Kind of sounds reasonable until you go and put your hand on the rail and its still cool even after we're at full operating temps for extended periods. The leaky injector idea sounds plausible too, but the guy who suggested that also suggested that we would have a rich condition at startup, which it is not. Whenever I have the issue its always lean...like above the measurable range on AEM wb. I had it pegged as faulty IACV but it seems our friend has ruled that out. I need new injectors anyway since 750s are at 90%+...you can tell how old they are...who the hell uses anything below 1000cc anymore lol?

 

Mine idles around 17-18:1.

Weird that so many of us have the same issue.

Software issue? Do we all run Tephra 7?

 

I'm also wondering now if it is an issue with the tephra mod v7. I don't have the time to read through the billion pages in that thread, so I won't bother.

I'm happy to report my findings as they come in. However, you guys may be waiting a little while as I only get a little time here and there to work on the car. And now that it is already half apart, I'm considering a head gasket job. I suspect the HG is on it's way out and will confirm with a leak down test. But if it is in fact leaking, I might as well get it done now and over with.

 

Edit

 

FWIW, i don't think it's a hardware issue. i just rebuilt my engine, so all seals and gaskets have been replaced. again.
i've boost leak tested the CRAP out of my car. i've tried different IACVs. i have a different MAP sensor. different MAF, blah blah.

i literally noticed the change when swapping from Tehpra 5 to 7. i once went back to 5 and had no issues, then back to 7 and have it again.

i'm not saying that's the issue. it could be coincidence and/or it could also be that i'm not remembering everything exactly right over the past few years. but i do specifically remember thinking ver7 was making my car run poorly, before.

so, i thought i'd throw that out there. if everyone having these issues is on v7, then maybe there is a link.

 

Mine is opposite from you guys. My car goes pig rich before trying to stall. I am also on tephra v7.

 

Just an update to my car specifically: I unfortunately found out my valves are leaking in cylinders 3 and 4. So the head is coming off for a rebuild :-(

 

Ouch that sucks. While the heads out though you could send your injectors out to be cleaned and tested. Its pretty cheap and I would be willing to bet most people in this thread have aftermarket injectors with enough miles on them to benefit from cleaning.

 

That is an extremely good idea. I bought the injectors used so I don't know how many miles are on them. I might as well get them sent out. Thanks!

 

Try to log injector pulse width.

You could be having issues because the injectors are running at a low enough pulse width to be at their 'non linear zone', so to speak, which for older tech low imp injectors running ballast resistors, would be quite high (no exact number, but probably somewhere around 1.6 ms). Having improperly calibrated dead times would make the problem worse.

First things first though, make sure the injector dead times are set up properly. What kind of fuel pressure are you running? Most injector manufacturers publish their dead times at approx. 44 psi. The same low imp injectors running ballasts would have very different dead times compared to running peak-hold drivers.

 

so, in essence, the injectors are "too big to idle"? without some tweaking, that is. i wondered about this because my car idled GREAT with 1050s. nothing but trouble since swapping to 1450s but i changed a few other things too.

 

Great idea! But unfortunately for me this will have to wait as I am now in the process of rebuilding the cylinder head.

 

I just checked my logs and I'm not getting anything on my fuel trims. I figured it was primarily o2. Changed with Denso version and still nothing. Weird thing is I only get a random misfire code (no other cel codes for bad o2).

Maybe shell out the $350 for the oem o2?