RPM drop and stall on load at idle

[pwuser161684645588]

I'll have to adjust it back. The engine has rotary iacv so I usually adjust by unplugging it and blocking the bypass port as rotary valve becomes sort of free, then adjust base idle to near 650 as spec is 700 +-50, base idle near 650 and let iacv fine tune b/w 650-750.

could you explain this scenario a bit brother??

[rajaatta]

You need either exhaust analyzer or widebody exhaust analyzer to see the fuel mixture.
Yes pulse width is modified but on scan equipment it is hard to see it.
Actual figures comes on analyzer.

[thatdevsherry]

It's the method I used for adjusting the butterfly of throttle. All mechanics I've seen adjust it while the IACV is connected, which is wrong.

I got to know about this method by googling so I wasn't sure if it's correct. It does make sense though. Also I believe @Xulfiqar has also talked about this method in old threads.

The goal of IACV is fine-tuning idle, not being responsible for keeping the engine from stalling.

I only have experience with baleno which has a rotary idle valve (spinny shaft) with 3 wire connector rather than 2 wire.

Once you unplug the connector, the iacv doesn't go into full close position, rather it's still in an open state, even if you fully rotate the coil side, there's still opening in it. So I use a cloth or something and press it with my thumb on the iacv opening in the throttle body which blocks air from going into iacv entirely, even if it is open.

This fully blocks the iacv port. Now all air has to go through butterfly solely.

This is the time to adjust base idle i.e. how much air is going through butterfly. Then adjust it to somewhere near intended idle. For baleno its 700 +-50, so adjust it near 650.

Once this is done, butterfly is adjusted. Now you can connect iacv back.

If you totally close butterfly, now iacv has to overwork to maintain the engine and not let it stall. Think of you as being hired to deliver pizza from shop to home. But now they tell you that you have to make the pizza too else shop will close.That wasn't your job xD

iacv is just to fine-tune idle and help with idle-up on loads. The butterfly should let engine idle at 650. Then iacv fine-tunes it to the intended idle by ECU i.e. 700.

[thatdevsherry]

Ah I see. I'll still double check that there is voltage change in trimpot, and then check that the voltage is changing on the ECU connector. If that's changing I'll take it to enercon again and adjust afr using the exhaust analyzer output.

Thank you

[pwuser161684645588]

that is very well explained brother! This is my first time hearing about setting idle like this. Btw, will it affect fuel efficiency or performance of the engine? will it also have any affect on butterfly's life?? I also have a Baleno, that's why im curious.

[Xulfiqar]

This is the actual correct way, its explained nicely in other brand repair manuals which use the same rotary valve iacv (some old volvos also use it)

[sameerulhaq064]

Great thread . Following

[thatdevsherry]

Affect on fuel consumption is minimal. This is the best idle you can get while keeping iacv from working less/hard.

Trying to go below won't work as even if you close butterfly fully, ecu will open up iacv to get to 700. However, opening up butterfly too much will use more fuel.

If a mechanic adjusted butterfly so much open that even when ecu fully closes iacv, it can't bring down idle. If that's the case your idle will be higher and use more fuel.

Butterfly is going to be fine with this adjustment.

if you fully close butterfly, it will get stuck when cold, and have sticky behaviour when opening it up due to big vaccum change. Makes it hard to smoothly get on the throttle without giving a jerk.

Other than that nothing changes with performance. Only affects idle and off-on throttle transition.

[thatdevsherry]

So I measured voltage from middle pin of trimpot to chassis ground. surprisingly the voltage being shown was 4.7V. Rotating didn't change it.

Yet the CO% was 0.48% (lean) at enercon.

I then checked the voltage in ecu connector. The two pins (CO adjuster resister & ground for CO adjusting resistor). No voltage.... Weird because one of the diagnostic pins is also not showing 5V. Which isn't an issue but CO% one is. I mean I'm doing the same probing and the electric load voltage shows up. CO% isn't.

Even changing to chassis ground didn't show any reading.

Will have to consult an electrician it seems. Most probably I'm doing something wrong. That or ECU is totally ignoring trimpot and going by it's base fuelmap (aayein). Zero knowledge if it can work like this.

EDIT: manual says to check voltage when couplers are connected to ecu. i was doing with coupler disconnected. Not sure if that's the cause. Prolly is because they might need reference voltages by ecu. Will see if I can try backprobing or something without breaking my back in that confined space.

[Xulfiqar]

You need to do the test with everything plugged in, as the variable trim pot takes reference voltage from ecu itself.

Use backprobe pins to do the test, long time ago I made testing harnesses myself from junk ecus (desolder the connectors from it)

From those connectors I made a breakout harness which you can front probe easily - i made the harness about 30 inches long so I could probe it while seated.

Keep it up!

[thatdevsherry]

Thank you for clarifying. Love the harness idea.

I went over the wiring diagram once more because the pin numbers and connectors are named differently. Connector names were different and pin number depends on which side they were being shown from.

3 wires were connected from co adjuster to ecu and I was able to find out what they are after doing a bit of braining over the connector diagrams.

VCC: power supply for sensors (reference)
CO: CO adjuster signal voltage
COE: GND for CO adjuster

Makes it so much easier to understand. I could see the 3 wires in trimpot but never knew what the third one was. Now I know which one's which

[thatdevsherry]

Today's update

So I couldn't fit a needle behind the ecu connector. I went back to the trimpot to measure voltage.

Power source to gnd: 5V
Signal to gnd: 4.7V

Moving the trimpot did not change the signal voltage.

Checked voltage on cousin's baleno, signal to gnd was 3.2V.

Wiggled out my car's trimpot and no resistance was coming out in the pins. Removed the cover where trimpot is soldered to male connector, 2 solders were broken.

Cousin being handy resoldered all 3. Resistance was now seen in male connector pins.

Attached trimpot to ecu. Signal to gnd was 2.7V. Rotated knob, voltage was changing now.

Not having exhaust analyzer, adjusted to the other baleno voltage i.e. 3.2V.

Felt a bit of fuel in exhaust, adjusted back to around 2.8V.

Seeing water coming out of exhaust. But now I need to adjust CO% at enercon. Last visit would've been wasted if I tried to change it because trimpot wasn't functioning.

However, first I'll replace the intake manifold gaskit as a precautionary measure. While doing so I'll check if rotating trimpot changes injector pulse width now.

Although I couldn't feel any difference when adjustin trimpot when car was running.

But some progress has been made. Maybe this isn't the issue but still, something broken was fixed.

[atifsrehman]

Great read , at least now I know how to adjust RPM on throttle body. Thanks mate...

[thatdevsherry]

Todays update

i hooked up a scanner to confirm trimpot is changing injector pulse width. It was.

Went to enercon, initial reading of CO% was 3. No wonder my motorway driving gulped fuel xD

Brought it down to 1.05 - 1.20. Slightly richer side on the spec (0.8 - 1.3) but still within it.

RPM still drops though. Car hasn't stalled as of now. I haven't replaced intake manifold gaskit. Won't do it until I verify with a smoke test.

Keeping an eye on other components (ignition etc) in case something feels off there.

Cousin also had his baleno engine rebuilt. Faced stalling when braking near a uturn. Happened only twice. But he also noticed rpm dropping too low sometimes. Possibly related.

[atifsrehman]

Can you do DIY smoke test I am just wondering ??

[thatdevsherry]

It certainly is possible. Just a bit of pain to set it up. Will try.

[thatdevsherry]

So I was able to stall on idle by following:

1. Move steering full lock
2. Let go near full lock so no pressure is being applied and wait for it to go to idle rpm
3. move steering to lock which is just a bit of steering and hold there

engine either:
- vibrates with rpm drop near 500 and die
- vibrates with rpm drop near 500 and recover

interesting to note that psps on signal is super fast. on normal steer rpm shoots up.

So this is interesting that even when the psps switch turns on during the above method, engine has a hard time instantly raising rpm and instead drops rpm and dies sometimes. Whereas on normal psps on at steer it shoots up to 1100 without hesitation.

The fact that rpm drops and it vibrates is showing hesitation to raise rpm. It shouldn't let rpm drop low when psps is active.

todo:

• check intake manifold leak.
• check base ignition timing is correct since it's without distributor. there are documented ways to set ecu to base ignition timing and then to verify with timing light. but what i'm concerned is if its possible during rebuild they misaligned pulley and crank. not sure if that's possible to do. but if so, concerned for that. oh well better to confirm base timing shows correctly first.

[thatdevsherry]

So I changed the intake manifold gaskit as a precautionary measure.

The old gaskit was metal one so that was good. just that it had silicone applied around the intake holes. I didn't see any mention of rtv with metal gaskit in FSM so I installed the new one dry.

But no improvement. So that's not it.

Timing I have yet to verify. Not sure if this is it because the stall only happens when engine is at operating temp. And sometimes when braking and steering the rpm doesn't go down and hangs around 800 like it does when i rev and let off. It's where iacv takes over and then brings idle down.

Ignition timing is being controlled by ecu. Can see it fluctuate between 10-15 btdc on scanner. Just need a timing gun to verify that locking ecu at 5 btdc corresponds to 5 btdc on timing cover as well.

Even if brake booster checks passed, I now suspect it. At least one variable is now out of the way (intake manifold gaskit).

[Xulfiqar]

Find an oldschool vacuum gauge and check manifold vacuum when anomalies happen.

Isolate the brake booster and see if change happens, a leaky brake booster can cause loss of vacuum.

[thatdevsherry]

Thank you for the suggestion. Will check it out.

I did a rudemantary test by checking MAP voltage at idle with and without brake booster linked (and pressing brake when connected) but vaccum gauge is better for this as the sensor doesn't really make things obvious.

I also noticed engine won't start when really hot. Looks like my battery needs replacing. Super slow cranks and I tested voltage drop on battery when cranking and when engine was hot it dropped to 9.6V (maybe even when cold), and even going to 8.5V when trying to crank for longer. Has the daewoo MF battery that was present when I bought the car. Saw the battery autotmotive topic so will check if I can prepare a khushboo battery myself.

I readjusted my base idle with a new strategy.

Used the isc actuator message to command the lowest idle (500) and saw that rpm dropped to 500.

(Anime Nani effect). I had adjusted by blocking iacv with cloth and idle was ~630. But commanding 500 idle caused rpm to actually drop to 500.

I then adjusted throttle stop-screw a few times until rpm went above 500 and then the commanded idle (500) caused isc duty cycle to go to 1% (full close) trying to bring idle down. Helps because I wanted to close iacv fully so I can adjust base idle. Then adjusted the base idle to near 650 when iacv duty cycle was 1%.

So the base idle should be better now. Commanding 500 makes isc duty cycle 1% (full close) and butterfly is mechanically open to make rpm be near 650 and not below it. Confirmed that closed throttle position is still ON when throttle isn't pressed. Pumping brakes and holding makes rpm drop to 550 and at 550 isc duty cycle increases and brings it back up.

Was coming to a u-turn and when braking the rpm had already dipped near 550. As soon as I turned the steering wheel fully, felt engine vibrate and I was 100% sure that it'd stall but it recovered. Thinking maybe I should increase base idle further to 700 but FSM adds 50 tolerance (700 +-50) so not sure where exactly to set it at as setting to 700 means on idle isc can't bring it down further. But it might make isc respond at a higher rpm than 550 and prevent stalling.

Adjusting base idle this way did improve it. I can see the needle dropping to above 500 mark whereas before it would be at 500 mark.

The to-be-replaced battery shouldn't be causing issues when running I guess. On cranking it makes sense, but when engine is running the ecu reports 13.8-14.4V. Better get the battery out of the way first. Would be pretty embarrassing that I stall on a turn, and then proceed to start it and it just cranks in slow motion and I just smile to the traffic I blocked.