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1G Rough idle on cold startup, kinda disappear after driving 15 seconds

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dreadnought369

Probationary Member
4
0
May 23, 2021
Europe
Hello ya'll, kinda new to the DSM world but I learned so much lurking these couple months. I recently bought a 1G Mitsu eclipse, 100.000km (62.000 miles) in good shape, practically stock, GS (European trim, 150hp), LPG conversion kit installed and working.

Everything is fine, the only issue I'm encountering is kinda annoying: on cold startup, the engine doesn't spool high enough and after a brief power-on peak at 1500 RPM, it just drop and dies. I can try how many times I want but it still won't power on well and stabilise. I have to disengage the clutch and accelerate while remaining stationary or directly driving for 15s or so, after that it idles at 750 RPM, so the correct amount by reading online. It's really annoying if I have to get out of a tight parking stop. Once I'm driving, I have almost zero issues with rough idling. Engine may dies if I'm using the AC and coming to a stop. I know about having to adjust the BISS screw, but the stable 750 RPM once warmed up seems to indicate it is set correctly.

There doesn't seems to be any vacuum leaks, it's an aspirated engine so not much stress on the hoses. I've heard it might be an issue with the o2 sensor needing to warmup before sending the correct amount of air, but I've read conflicting information. Engine seems to be running correctly (no visible black fumes coming out, although it might be running lean...).

I'll be going to a mechanic soon but he has no experience in DSM (kinda rare nowadays where I live), so I wanted to narrow down the culprit, maybe if any of you is in the same boat and solved this issue.
Sorry if it seems stupid, but most posts online are talking about too HIGH rpm on idle, instead of too low.

Any help is kindly appreciated :)
 
Wait; your car runs on propane? Or does lpg also stand for something else?
That’s different.
I could certainly see why there might be some drivability issues. These don’t sound too bad among the spectrum of ills that folks post about with their dsms, just saying. Perhaps describe the lpg thing a bit more. I’m intrigued that things improve after only 15 seconds. Definitely not enough time for too many things to warm up.
 
Wait; your car runs on propane? Or does lpg also stand for something else?
That’s different.
I could certainly see why there might be some drivability issues. These don’t sound too bad among the spectrum of ills that folks post about with their dsms, just saying. Perhaps describe the lpg thing a bit more. I’m intrigued that things improve after only 15 seconds. Definitely not enough time for too many things to warm up.
Yes, a LPG conversion helps in switching from gasoline to propane at any time you wish. They installed a switch on the left of the small coin tray, near the handbrake. That switch changes the fuel used, so I have two separate tanks now. This is all to reduce running costs, since propane costs almost one-third of gasoline with no real perceptible performance drops. It is a fair bargain. But installing the LPG kit comes with some complications. Namely, the engine bay is stuffed with wires and hoses that bring the propane directly into the engine. Also, there's some modification on the throttle wire, since it makes a longer travel to get into a new electronic box for LPG, before actually opening the throttle valve. IDK if this somehow tampers with the usual startup sequence...

Still, I guess I was lucky in buying a relatively low mileage eclipse that seems to have been tended well and not aggressively used. But yeah, it is really weird that I need to throttle up for a few seconds to successfully start the engine up. It doesn't happens every time tho, sometime I can just power the car on the first try, even if the RPM still usually drops below 500 for a couple seconds before stabilizing, making the car vibrate a bit.

Kinda weird, uh?
 
And it does this on gas or propane or either?
Propane mode only triggers after the engine has been running for some time, it needs to sense a hot engine before activating. So it always power on using gasoline. But the idle issue already existed when the LPG system was out of order. Now that I’ve repaired it, nothing changed.
 
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