RPM drop and stall on load at idle

[thatdevsherry]

A good update.

Opened iac valve fully. removed silicone. added new rubber gaskit. Used the iacv valve that came with throttle body (was using another one) and I soaked it in machine oil for 10 15 minutes (or i should say bathed it xD). Bolted it to throttle body. Cleaned iacv solenoid with contact cleaner and pen-pineapple-apple-pen.

O-ring b/w solenoid and valve body was missing in my iacv before. red flag

So added a new o-ring and started her up.

Used the expensive scanner to do actuation test. RPM dropped to 500. No idea why that happened since I had adjusted base idle before. Oh well I fiddled with the actuation test 2 3 times (because each time i redo it ends up at a different rpm) and ended up with base idle of ~675.

Got home, started logging the brake and steer and..
PSP switch started activating early (90-100deg) from center.

Tried doing brake and steer at full lock, car vibrated as if about to stall but it recovered. Did it 5 to 10 times and it didn't stall once. Behaviour similar to my cousin baleno that I also couldn't stall.

Don't know if it's related that the early psp activation is a sign that car won't stall at full lock. Because I'm pretty confident I can stall it as I did before. Now I couldn't.

Will check if psp switch behaves the same at warm temp again.

Thinking I should up the base idle further to 700 or in other words, making iacv flow duty be at or near the minimum level mentioned in fsm (5%).

Will update on situation on next drive.

EDIT: I would've preferred if it acted similar to the iat disconnected flow because that's just perfect. But guess its suzuki being suzuki. Sensors being too sensitive i guess.

Barometric and map seemed to be fine. Not sure if ecu has a barometric pressure sensor inside but when i turn ignition on, barometric is at 101.57 kPa. As soon as I crank (even a teeny tiny crank that doesn't start engine) the baro value changes to 95.71 kPa.

MAP at ignition on is 95.71, so maybe ecu first uses hard-coded one and then on crank uses the map value to set barometric pressure for iacv and fuel adjustment.

Screenshot of me doing the brake and steer today when car didn't stall. the purple line is at 500 when 0, so the rpm sometimes dropped to 400 as per the logs. Maybe better to add some noise filtering or average window in visualization logic.

Engine speed - ISC flow duty - PSP switch - MAP sensor voltage

Above seems fine as ISC flow duty goes up as soon as psp switch is activated, rpm takes a while to come up, maybe it's the lag in milliseconds that it takes for iacv motor to move the shaft.

Engine speed - ISC flow duty - PSP switch - battery voltage

Looks about fine. Goes to around 12.8V - 13V sometimes so not sure about that. But otherwise seems to remain in good zone (as per me... looks bad actually but self soothing). Though drops are momentary so maybe it's all good.

Engine speed - ISC flow duty - PSP switch - injector pulse width

Injector pulse width does go up, should check if it's any different with IAT sensor disconnected.

Engine speed - ISC flow duty - PSP switch - Ignition advance (calc. not confirmed but should be near)

[Xulfiqar]

Set base idle to 700 rpm then retest.

[thatdevsherry]

Is setting to 700 fine right? Not sure what FSM means when it says idle should be 700 +- 50 with isc duty of 3-30%. Most videos I saw were setting just below intended idle. FSM gives a range so not sure what's the best base idle to set for it.

I'll move to 700 while keeping isc flow duty >= 3%. Will retest.

[Xulfiqar]

On cars with mechanical throttle i work on the principle that your base idle should be idle and your isc then takes care of additional requirements.

But you should not simply use the rpm gauge as your instrument, its for entertainment only, use something true and proper, scan tools can give you that data, if you dont have it then calculate it from the ignition coil firing pulses with a dmm that can measure Hz

[thatdevsherry]

Thank you for sharing this.

So FSM says 700 +-50 tolerance so base idle should fluctuate around 700, not below it. ISC to be responsible for idle-up and handling other loads which drop rpm (small steering that don't activate psp, radiator fan, and even notable things like power windows which drop rpm and don't signal ECU directly).

I'm not using the rpm gauge for adjustment. It's pretty inaccurate below 1000.

I had replicated the isc actuation test from a scan tool that a nearby garage has. RPM calculation is somewhat close (15-50 diff).

My tool showed base idle above 700, which seems wrong as the expensive one was showing around 675 so I'll adjust base idle to 700 using their scanner and report back.

Sharing some videos below for fun (and to show how I'm adjusting base idle etc).

@pwuser161684645588 the base idle ones might be helpful to you. I didn't show the actual adjustment because I was caught off-guard with the low base-idle. But it's pretty much a lock-nut and an l-key bolt thing that you move to change stop position of butterfly. It's near the mechanism where throttle cable end attaches to throttle body.

base idle using isc actuation test 1/2

base idle using isc actuation test 2/2

isc actuation with isc flow duty changing

[pwuser161684645588]

No. The starter spins at the same speed all the time no matter the temperature of the car. Something heat soak related, which is gonna be a big problem to find.

[pwuser161684645588]

Yes, i was thinking the same. Although fuel pump was new (2yrs old now) pressure test was also good. And the injectors were cleaned and flow tested about 2-3 months earlier. So i wonder what the issue might be. Ignition coils? Sparks Plugs?

[thatdevsherry]

I haven't yet done a pressure test on mine. I did check injectors and they were all consistent.

Did a rudemantary test by having throttle slightly pressed. FSM tells that if warm engine starts easily with accelerator depressed then check idle system. But it started late so it's not idle system. I would've banged my head against the wall if it did because I've gone over iacv so many times

Next test to try is priming fuel pump a couple of times before starting warm engine to see if it starts early then.

I doubt it's the ignition coils and plugs. I don't see any other issue when driving related to them so it seems unlikely they'd cause this behaviour.

[thatdevsherry]

So I took the car out for a short trip.

Was just near home and car was at operating temp, I braked at a slow speed (around 10-20kmh) and hadn't yet turned the steering wheel for a right turn.

RPM suddenly dropped to just above the 500 mark. Car was vibrating. I was at maybe 1kmh with clutch and brake pressed. Most of the time it keeps the rpm above 750 mark when I'm braking with clutch pressed. And now it was just above the 500 mark with engine vibrating. Clutch and brake pressed, no steering input yet.

Parked home and did brake and steer test, car isn't stalling. This was a bit new as rpm had dropped near 500 braking in a straight line. PSP switch has moved to near full lock again. But hey, engine not stalling with my tests. We have some progress and I'm a bit happy!

Almost all the time i brake with clutch pressed it drops to above 750 (not at 700 idle) and at this instance it dropped to just above 500.

Worth mentioning it's still at the 675 base idle. Yet to move to 700.

I do remember going above causes issues (like a mechanic once did) and when ac turns off or on it drops rpm a lot before adjusting. Prolly cuz rpm is so off that default idle up trips it out and it has to readjust.

Might take it out on an empty road and see if i can replicate the rpm drop and log it because it's intermittent.

My naieve thoughts:

At idle, rpm drops to 700 idle after rev up and brake press. Normal.

If vehicle speed not 0, it holds it above near 750 (not 700 idle). I was expecting it to drop to 650-700. But currently it somehow holds it at ~800. I have clutch and brake pressed so no engine load except brake. So the only signal that is different has to be VSS.

As it comes to a complete stop it drops rpm further to around 650-700.

Not sure if it's related. Because we have progressed and car isn't stalling with brake and steer test. We now have this new behaviour.

Better to log it with vss data to see how isc flow duty is influenced by vss.

I couldn't find a kabli map sensor to test so currently have to monitor the one that's currently plugged in. Used my cousin's map sensor some time ago when brake and steer caused stalling. car still stalled with his sensor. But it's kinda stupid to use his car's one because his car also has somewhat related issue... so that wasn't very helpful.

TLDR: PSP moved back to near full lock. Brake and steer not causing stalling anymore

But new intermittent issue. Brake with clutch pressed when vehicle speed > 0 sometimes drops rpm to near 500 and keeps it there for some time. No steering input. Just brake and clutch pressed while car is still rolling.

EDIT: Could it be fuel pressure regulator? Not managing changing fuel pressure when going from acceleration to sudden idle?

[thatdevsherry]

Thank you for chiming in.

I had some electrical work done on it some time ago. There was a short somewhere that would cause engine to immediately stall when you pulled on the wiring.

Once that was fixed, I haven't yet gotten the camshaft DTC again. So that's a good sign. I do remember the battery voltage was also moved closer to actual. Need to check with DMM again to see the difference b/w actual and what ECU reads.

I checked voltage drop at each ground point in the engine bay. All's good.

I haven't yet dove in to the cabin wiring as that seems unlikely. The flasher relay does have a weird behaviour, but it was present before rebuild too, so that remained a constant.

I do like the idea of disconnecting non-essentials! That could help.

I'm currently exploring the fuel pressure regulator being bad. Don't have a gauge close by but the following symptoms are present that are supposed to point to it:

• engine cranks for longer before starting when engine is warm and left off for ~30 or more minutes (regulator is supposed to be a one-way valve and retain pressure, seems to be dropping it. Although cold start is super duper quick)
• intermittent idle drop to 500 when braking (most of the time it stops to 800, intermittent it drops to 500. Regulator not reacting correctly to changing pressure? e.g. getting stuck "sometimes")
• quite a decrease in fuel economy (I could get 13-15km/l before rebuild, now I hardly get 10-12km/l. Naively suspect regulator maintaining too much pressure as car seems to pull a little "too good")

I have yet to log coming downhill and braking and recreating the 500 drop. I can then verify if ISC flow duty had increased during that drop or not.

[thatdevsherry]

Update

I went ahead and changed the fuel pressure regulator with a kabli one. Doesn't seem like the right one for it and had to cut the metal return pipe as it was touching intake manifold.

Ordered the correct one from aliexpress with same part number. Hopefully quality is good and that one works fine.

I took the kabli one for a drive to make sure it isn't sticky or something. Car still pulls good. No hesitation.

Checked the behaviour by pressing clutch at 40-50kmph. RPM dropped and settled around 900-1000 and stayed there the entire time VSS was > 0.

Not sure how the behaviour was with the old regulator, but one thing I noticed is that on the old regulator when I approached a speedbreaker, the rpm would drop to ~800 and then as I was going over the bump, it would sometimes drop < 750 to near 500 mark.

Now, I went over the same speed breakers but the rpm never went below the 900-1000 point, even as I was going over the bump.

Also I'm not confident the kabli one is right because the return line goes up vertically. Not sure if that will cause fuel to come back into it or something. Waiting for the other part to arrive but will keep experimenting with this one for now.

Worth mentioning, when at idle and stationary, moving steering very slowly causes idle to drop to ~500 mark, car vibrates a bit and after ~5 seconds the idle starts going up. This happened before too. Pretty sure ECU never commands ISC until the rpm starts going up. Need to confirm with logs.

[Xulfiqar]

Do you see fuel leaking from the vacuum signal port for the FPR?

[thatdevsherry]

I took a look at the hose when mechanic took it out. It wasn't wet. But my dumb brain said to put it in my mouth and squeeze in out for fun, so I did.

I was able to smell fuel. Or tasted? I think it was smell otherwise I'd be dead. Don't think I should've smelled that even though the hose was super dry. The hose was attached to the old FPR when I did that.

EDIT: I think you mean checking the kabli one... I'll check it and update.

[Xulfiqar]

A leaky fpr is checked on running engine, remove the vacuum line and check if fuel leaks,

You may need to wait for a while or use a tissue paper to see if fuel wets it.

Please do not put stuff into your mouth or nose.

[thatdevsherry]

I haven't yet checked FPR, will check when I find time (or check the aftermarket part if it arrives quick).

I readjusted base idle to near 700 and it seems to be working fine for now. RPM drops are there when I do slight steering at idle (logs attached below) but I believe this is normal for this engine (think it was like this before rebuild too).

I did some tests at base idle (isc flow close) to get an impact of how different loads are affecting the engine idle without ISC intervention.

Slight steer at base idle (isc flow duty 1% (full close))

Drop of ~175 RPM. Not sure if this much load from P/S pump is normal or not. Cousin's noisy pump hardly puts any load on slight steer. AI said it could also be that his pump is worn and has less resistance. No idea. Have to test slight steer on his car with isc flow closed. Or mine has too much resistance e.g. relief valve sticky, or belt tension is too tight (TODO).

Brake press at base idle (isc flow duty 1% (full close))

Negligible impact on RPM

YT links

Brake and full-lock steer updated. Does an up-down-up before stabilizing. Expected it to be a single smooth transition up. But eh, no stall ever sine IACV was installed properly. I happy

base idle slight steer. I notice steering pushing back if i reduce steering pressure a tad bit (visible in video). Normal?

idle load test. Mostly to show off my prototype scanner. No real value addition. Probably need to adjust when to show "red" cuz either this voltage is normal or there is an issue xD

After a few drives I'll check if rpm does the yeet-to-500 like it did when I was braking straight. If not, I'll mark this topic as either complete or go ahead with a rename or new topic to address "RPM drop" if it becomes an issue. Awaiting aftermarket FPR for now.

EDIT: I might be chasing a few different issues. Before rebuild I remember steering would drop rpm, but this is excessive.

Cousin's steering with PSP

Haven't tested without ISC intervention. But slight steering does not put much load on engine, rpm remains stable. Didn't log but I'm pretty sure the rpm remains stable when holding full lock, unlike mine which bounces around initially.

My steering with PSP

Was holding at lock for a few seconds to see how it stabilizes. Visible that the RPM goes up to 1000, then drops to ~575, then to 800, and pretty much stable then.

[thatdevsherry]

Took it for a drive. Only drop I noticed was when I pressed clutch at low speed and steered fast into a parking spot, but drop felt normal. No weird behaviour. Didn't have scanner and the rpm gauge is inaccurate. No vibrations felt.

Might just be normal for P/S to have this much load.

I tested slight steer and when it drops, isc starts recovering it back in 1-3 seconds. Just slight vibration in car when it drops to low rpm, nothing obnoxious. Its a 2005 baleno, pretty sure this can be considered "normal"?

This is all after using the kabli FPR. Today when I pressed clutch at low speed rpm dropped to just above the 750 mark, and kept there. I then stopped the car to see what it does, it was keeping rpm around the 750 line the entire time VSS > 0, and when i stopped it moved it a bit lower to 700 intended idle.

One other thing is that when i do full lock steer into a street the rpm don't like shoot up, they kinda just.. hold the rpm i think somewhere above the 500 mark initially and then bring it up to just below 750 mark.

I'm happy though. Maybe this is intentional. It's holding rpm at full lock pressure. Not really supposed to shoot up rpms all the time.

I think issue is resolved now just a few more drives to make sure it is. Drive is so much better. Full confidence that car won't stall no matter how much I steer in a parking spot, which was the original issue.

What helped:

• IACV (rubber gaskit, o-ring, spindle oil the heck out of it)

• Good base idle (675-700)

(Above 2 did same time, brake and steer stall was fixed immediately)

• FPR (No drop to 500 noticed when braking with clutch in straight line after replacement)

A big thanks to everyone who contributed to this topic.

I was living with this issue for about 9 months after rebuild. And only about 2 months ago I got frustrated and took it into my own hands and this topic was made, and we got the engine into a better state and fixed issues.

EDIT: For anyone interested in the scanner I worked on, I also made a topic for it.

[thatdevsherry]

So after a couple of drives. Marking this as complete.

RPM sometimes does drop when backing up and forth in parking spots etc and braking straight, but not too much so as to cause vibrations. Engine just becomes... a bit too quiet. My P/S pump "might" have some issues because on full lock I hear an intermittent high pitch noise (not belt, and not groaning), but meh. It is fine.

But I've tested full lock turns when the rpm is down in parking spots and engine isn't stalling.

Can it be better?

Don't know.

Am I gonna put more effort into it?

No. As long as engine isn't stalling on full lock load, and the rpm drop is not so much as to cause vibrations, it is as good as it can be for me.

I also tested on a downhill road and when braking rpm had dropped down near 500 mark but the vibration was not too obnoxious. A tiny vibration that isn't concerning. I steered full lock with brake pressed and psp switch managed to bring rpm up. So happy I wanna cry.

Thanks again to all who helped out

[thatdevsherry]

Well well well. Issue appeared again as I was testing it in a "kacha" road.

When I came home and retested it almost had stalled then recovered. RPM went so low I saw the oil light come on for a quick second.

Something is still up. No idea what the guys did during rebuild that is causing this.

@Xulfiqar I had shown in a post above (92) that when I locked ISC duty to 1% and then steered slightly, the rpm drop was around ~185. Isn't this too high of a load from P/S with just very slight steering (~45-90deg)?

The recovery of rpm from a certain stall kinda shows iacv is working fine, just that it's really at the edge of overcompensating and fails in certain conditions.

[thatdevsherry]

So even though brake and steer test makes it just sort of die and get revived, it hasn't yet stalled on normal driving.

If it ain't broke, don't fix it.

[pwuser161684645588]

brother could you please make a video on adjusting the throttle. I tried some mechanics and most of them said 'aisay ni hota'. if you could just explain it to me in detail how you do it via call or chat, it would be great help. I also have manyyy manny more issue but that's for a later day. Thank you.