Engine RPM increases too much when using AC - 2008 EFI

[RehanBhatti]

Good to know that your alternator is fine. Did you ever get a chance to scan your ecu? If not then scan it, there might be some error codes store in its memory. Those codes are very helpful to diagnose many issues.

[aminjafer5441]

I don't have a compatible scanner and even the electrician didn't have it on hand. The CEL is off, could there still be any error logged in the ECU?

[RehanBhatti]

You can buy a cheap (in price) bluetooth scanner Vgate ELM327 1.5V and can monitor live data from your ecu. That scanner works great with SZVIEWER app.

[aminjafer5441]

I've just ordered the scanner online. I'll try to see if I can get any information from the diagnostics regarding this problem and post back on the thread soon.

[RehanBhatti]

Great. Make sure that your scanner is same in this pic

[Xulfiqar]

check if your ECU is actually going to closed loop mode, on cold start the ecu will raise rpm to maintain a stable idle, if this is not released when warmed up, the rpm will shoot high.

the closed loop bit is triggered by the coolant temperature sensor.

[aminjafer5441]

Yes I believe it is going into closed loop mode as the Idle rpm reduces to about 800 once engine is at optimal temperature.
Even when Ac is on and compressor is engaged then the Idle goes to about 900-1000rpm but once the compressed trips and ac switch is on then the rpm shoots to 1800 and recently it went to 2000 rpm then started bouncing between 2k and 1.5k rpm.
If I turn the AC off then idle returns to normal.

[aminjafer5441]

I've made a few videos to demonstrate the issue here. It seems to be an electrical problem other than IAC valve as I've changed IAC valve sensor twice and even swapped throttle body with kabli one with same symptoms to check if issue is in IAC valve or throttle body.

1. The car idle returns to normal when AC is off, at no point during driving does the idle ever stay stuck high when AC is off.
   video: https://drive.google.com/file/d/1FaSAqBmwMWVYhViS3qQ1CXfubR8iQF-F/view?usp=sharing
2. The car idle shoots up when ac is on and the compressor trips (compressor clutch disengages) and the car is moving not stationary.
   video: https://drive.google.com/file/d/1FcswK9I3KvNr9iO9D5YfYYE19uOC4oFl/view?usp=sharing
3. When car is stationary and AC is on then the high rpm issue is not there. However there is a sharp drop in RPM when the compressor engages which eventually recovers in a few seconds and when it disengages the RPM jumps a little high above idle and then slowly returns back to normal.
   video: https://drive.google.com/file/d/1FYlP0SEWbH-99axbDH4W8BsUVlX7r47-/view?usp=sharing

Basically I've had two well know electricans also diagnose the issue but to no avail. They say that if car is not giving any other problem then keep driving as it is but the car is actually dangerous to drive with ac ON as I'm used to engine braking and sometime when the compressor disengages when I'm engine braking the car suddenly surges as the RPM shoot high again.
Please do give your two cents about what could possibly be the issue here ?

[RehanBhatti]

Try to scan your ecu when you driving with AC ON. And make a clear video with help of screen recording app of your cell phone. We will try to observe any abnormal activity by that video clip. It seems a tricky situation.
Btw, did you check your TPS voltage at fully closed throttle?

[aminjafer5441]

TPS voltage is 0.83 volts at 0% throttle. I will try to record a video of the diagnostics with AC on and then post back.

[aminjafer5441]

I was really busy so couldn't update on the issue. Just recently I used the diagnostics to check if the AC magnet clutch reading on ECU reads correctly and found out that even when the magnet clutch is disengaged the ECU shows it as on.
And when the car is moving then the IAC position increase to 30% (normally at 16%) or more regardless if the AC compressor clutch is engaged or not.
Do you think the ECU is getting false reading of AC compressor load which is why it keeps RPM up even when Ac compressor is not engaged?

[RehanBhatti]

I have never know that SZVIEWER show AC diagnostics too.

[umair149]

If Ac clutch is disengaged but ecu says its engaged then it could also be a bad clutch.
Check if ecm is providing ground to AC main relay coil in this scanario to turn it on, check if relay is correctly working and providing voltage to ac clutch but clutch is not on, then u have an issue in ac clutch.

[aminjafer5441]

Thank you for the explanation. I think I figured out the issue. The AC card has been bypassed by the previous owner and some "ustaaz" electrician has put a manual thermostat.
I'll have to pull apart the wiring and see wether the AC clutch signal wire going to ecu is directly attached to work with AC button.
But what confuses me is that it should have had the issue last summer als but it was actually working normal then.

[aminjafer5441]

Yes there are a lot of readings available. I accidentally double tapped the screen and it displayed all of them.

[RehanBhatti]

Would you like to share your short term and long term fuel trims

[aminjafer5441]

[pwuser156659349483]

hey do you have the picture of that ac card?or where it is located?

[aminjafer5441]

Nope. Unfortunately it was removed by the previous owner.

[pwuser156659349483]

oh! ok.Do you have cultus owners manual?