1FZ-FE poor cold starts and wont idle (SOLVED)

[thelal]

Got the car back from the mechanic. He said the issue was that the LPG system splices into the factory oxygen sensor wiring. However, someone in the past has removed the stepper motor for the LPG system, which means it now runs open loop, and doesnt need any o2 input. The splice connection was twisted and taped, so it would sometimes send dodgy signals interfering with o2 readings to the ecu when running on petrol.. thats why it was running good for a few weeks, until it wasnt. He's now disconnected the LPG wiring to the o2 sensor circuit and terminated it, so it wont happen again and the car is running good again... for now.. haha.

Glad you got it sorted

 

[petegangies]

Glad you got it sorted

Spoke too soon. Still playing up for the first 5 mins when cold on petrol. Bogs down, low power and slighty lumpy idle. After 5 mins of driving it's fine. Also runs fine on LPG. Next step will be to clean the injectors and inspect the fuel pump. Unless this is electrical related..then I'm stumped.

 

[thelal]

Spoke too soon. Still playing up for the first 5 mins when cold on petrol. Bogs down, low power and slighty lumpy idle. After 5 mins of driving it's fine. Also runs fine on LPG. Next step will be to clean the injectors and inspect the fuel pump. Unless this is electrical related..then I'm stumped.

bugger. At least it settles down after 5 mins

 

[petegangies]

bugger. At least it settles down after 5 mins

yeah, but highly annoying, and definitely needs to be sorted. Every time I solve/fix one thing, another rears its ugly head haha.. the never ending story

 

[petegangies]

bit of an update:

I backprobed the ecu and following sensors, tested for continuity and also voltage during operation:

• Engine coolant temp sensor - passed
• IAT sensor from air flow meter - passed
• Idle suction control valve - passed

I installed the second hand idle air control valve to see how it would affect the cold start RPM. It does idle a bit higher than the original one, but not as high as they normally do when cold. It looks like someone has opened up the original IACV. The 3 screws have been removed using vice grips as all had rough edges and damage around the head of the screws. Additionally, the shielding to the wires at the connector have been damaged (possibly the auto electrician in Newcastle when installing the loom). I tried to paint some liquid electrical tape over those areas, but it was very tricky given the limited amount of room to work. At least 4 of the 6 wires had been damaged. They all seem to pass continuity tests though, which is a good sign.

I also noticed some white writing up under the intake manifold. To my knowledge, the manifold had never been removed, but maybe I am wrong. Normally wreckers/scrap yards would do that when selling parts, but why on earth the intake manifold would ever need replacing, I have no idea, unless the auto elec removed it to make installation of the new harness easier and left notes to himself.

At this point, I'm at a bit of a loss. The car will consistently bog down when cold running on petrol/gasoline and clears up after a few mins of driving after it warms up. It will not do this starting and running on LPG—certainly sounding like a fuel delivery issue.

Next steps:

• re-test fuel pressure (this was previously done and passed)
• on vehicle injector clean (via some machine my mechanic has, that cleans the injectors without removing them).

The car has 152,000kms and is on the original fuel pump. I confirmed the hatch has never been opened.

Hopefully this will give us some further clues. If the original pump is okay, I'll still be replacing the hose and filter sock as preventative maintenance.

 

[petegangies]

for those curious as to what the IACV idle air control valve looks like dismantled.

 

[petegangies]

I managed to locate a brand new genuine IACV from an EFI parts supplier locally here in Australia. Unfortunately this did not fix the absence of a cold idle. The revs flare up momentarily before dropping. Which says to me that the ECU is commanding a fast idle when cold, but something is interfering and it pulls back. It also runs VERY rich on start up, puffing lots of fuel smelling smoke. I still highly suspect that this has something to do with the 2nd hand loom replacement my father had completed back in 2021. I'm not sure if this is also why the car bogs down when cold. The 2 may be separate issues.

Next step is to confirm the fuel pump and injectors have good pressure/supply.. then it will be off to an autoelectrician to backprobe every related sensor and plug on that loom.

 

[petegangies]

Update:

• New oxygen sensor (89465-69115) and new loom side connector (11178) both replaced
• IACV o-ring (90079-60004) and screws (90079-11022) replaced
• New a/c tensioner pulley (88440-26090)
• New oil cap seal fitted (90430-37004)
• EFI fuse pulled and ecu reset
• dodgy solder joint from LPG ecu into injector feed circuit repaired

Bogging down and bouncing idle issues seem to have been resolved. Oxygen sensor circuit was getting voltage bleed from heater lines into signal wires. Thus intermittentently running rich and causing the bogging and rough idle. Not sure if the injector feed circuit solder joint was also playing a part. Anyway, fingers crossed this saga is done with. Because I have a few others I need to resolve next.

I still don't have a proper elevated cold start RPM compared to others I know, but it is at least idling up to 1,000rpm now dead cold, and holding it for a minute from time to time. Interesting that it's not a consistent behaviour.

Thanks to all who have been on this long and painful journey with me—I'm taking the win for now.

Cheers,
Pete

 

[thelal]

..
Bogging down and bouncing idle issues seem to have been resolved. ..

Good Progress

 

[petegangies]

Good Progress

driving great, and not overly worried about the cold start RPM. It starts within half a key turn and idles smooth. I actually used the manual throttle lock yesterday and set it to 1200rpm to simulate a cold start, and thought... "gee that's a high idle for a dead cold motor"... so maybe I'm glad it doesn't idle up like it should when cold..haha!