Running Lean, idle hunting and stalling

chukarhunt

New Member
Good day all,

I have a custom swap, 1992 toyota pickup, 5 speed, with the non vvti 1uzfe. I am running a MS3 Evo standalone ecu with a wideband O2 sensor, no maf, just map.

Truck has been running great until a few days ago. Being a custom swap I dont know where to start looking, but hoping to get some insight.

I started the truck one morning, fired up fine then it quit and everything went dark. Turns out the main power wire to the fuse block broke off the battery. I repaired it later that day and started driving the truck again.

I quickly noticed that the high idle (i have the stock iacv functional) was hunting, will rev up high to 2k then back down to around 800 rpm, then back up, very cyclic.

While it is doing this, the afr is reading lean around 18, should be 14.7.

Driving down the highway it runs fine, but it runs lean around 18. If I give it the throttle it adds fuel and jumps up to 12 (normal for me. I dont have the acceleration enrichment tuned perfect) but then it quickly leans out again while still accelerating.

If I let off the throttle the engine dies. It will fire right back up, but after the engine is warmed up the idle hunts. It wants to die, but then revs up to 1200, then wants to die again. If I give it the throttle it revs right up, very snappy really, but then letting off the throttle it dies.

Everytime it starts right back up, but it is running lean and the idle hunts. The ignition timing is cyclic during this time as well, which it seems to be slightly advanced while it is cycling? I need to look at the map again to verify. The iacv is steady during this time, holding position from what the gauge is telling me.

What should I be looking for? I want to correlate the broken main power wire to this issue, but no idea what could be causing it to run like this. Thanks for the help! I will try to post a video of it running and with tuner studio open if I get the time.
 

chukarhunt

New Member
Forgot to mention the throttle position sensor is holding steady as well during the cyclic idle, at least what tuner studio is showing me.
 

gloverman

Well-Known Member
Have you blocked the air supply to iacv? That would confirm if thats the hunting. Otherwise have you looked for air leaks?
 

chukarhunt

New Member
I have blocked the air supply to the iacv, it still hunts. Do not believe it to be an air leak, but I need to get more starting fluid to confirm.

If I hold the throttle open, the wideband sensor reads near 21 or 22 O2, and the engine is misfiring a lot. Could the O2 sensor need calibrating or be bad?

I have a video of tuner studio running while the engine is surging, I will upload it to youtube and link it next. When I am driving and accelerating the truck still has plenty of gettup and go if I floor it. I put 6 gallons of fuel in the tank to see if maybe I was low on fuel, that didnt change anything.

I just did an injector and coil test through tuner studio. All the injectors fire when commanded.

The coils fire when commanded too, but coil A is much much quieter than coil B. Almost half the decibel. Dont recall if this is normal, hopefully someone has experience with this?

Idk what else to check. I put a timing light on the crank and the timing is surging, just luke tuner studio shows. The data loggers show that the crank and cam wheel pickup sensors seems to be working.

Thanks for any help.
 

chukarhunt

New Member
Here is the link to watch the tuner studio gauges. If there are other parameters I should show please let me know. Thank you.

 

gloverman

Well-Known Member
So if there isn't an air leak and it's running lean what happens when you add fuel on the map?

Fixing the misfire may sort the lean situation too as misfire would result in the lambda showing lean.
 

chukarhunt

New Member
Update.

I took your suggestion and increased the AFR table values to 10 from 14.7. Engine idle quit surging, and it was seemingly running smooth. In my endeavour to identify why, I figured out a part of the problem.

For some reason, the idle air control valve stepper motor was interferring with engine operation. I need to trace back exactly how I wired up the power wires, but when the engine is running, if I unplug the iacv, the engine dies, I lose power to the ecu. When I plug it back in, power is restored and the engine fires up.

So I went in to tunerstudio and turned off the idle control system entirely. I disabled everything that has to do with the iacv.

Engine started running normally again. But now, it was running too rich. I started the autotune in tuner studio to see what would happen, and the auto tune changed my fuel ve table dramatically. It leaned everything out, from mid 70s and lower 80s to low 60s to mid 70s.

And this made the engine really open up. I thought it was quick before, but this thing has never run better. It was slow in the high rpm range after 5k, but now it screams like a banshee.

So, even in my apparent piss poor job of wiring the truck, has anybody else ever experienced something like this? I am going to trace all my wiring back from the iacv, I probably crossed the power wires somewhere with the fuel injectors or ecu input.

I have to crack the throttle open now to start it. But it is a minor inconveniece. I will probably purchase a solenoid from a 6.5 diesel engine and mount it on the throttle. When the solenoid is energized, it forces a rod against the throttle, pushing it open slightly. Figure this is all I need for now.
 

gloverman

Well-Known Member
Well thats good news. For the megasquirt I use a 2 wire iac kit which bolts on. Easy as. Theres one on my youtube channel on a megasquirt video.
 
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