1UZ VVTI High Idle Issue

[Antanas]

Hi all,

I'm currently doing an engine swap and I've run into an issue that I can't figure out. This engine worked fine when I pulled it out of the a 400

My engine idles at 2000rpm +/- a 100rpm. Its a constant smooth idle, It advances the timing to around 35 degrees straight away and keeps it high, won't go lower, my stock 400 keeps it at 7.5 degrees at idle.

It starts up easy, runs for a second, pauses for a moment as if the power was cut then carries on running.

The things i have checked:
Vacuum leaks - none.
Fuel pump keeps fuel pressure up at 3.5 bar.
ECU works fine in my 400.
Checked/swapped MAF - no difference.
Checked/swapped crank sensor - no difference.
Throttle body isn't excessively open when running.
Checked timing belt - cams line up to TDC when cranks at 0
Stock transmission - runs the same when trans is or isn't plugged in, rpm does come down in gear but its still 1300rpm.
Coolant temp sensor works fine - idle comes down slowly with coolant in but only to 1600. Disconnecting it causes a rough idle and difficulty starting.
All four O2 sensors are connected and working.
Oil pressure is good.
Immobilizer works fine with the stock key.
Engine loom is uncut - only bits ive crimped is to plugs E11 and E15 with power wires connected on that massive fourth plug from the engine loom


Its something wiring or sensor related and i have no idea where else to check. Any help would be appreciated.

 

[gloverman]

Does the throttle body hum? Have you looked over the live data and checked fault codes? In the live data is BM+ listed as on? Are the aps and tps tracking correctly? Has anyone fiddled with the throttle stop screws on the TB?

 

[Antanas]

Throttle body hums. Only fault codes I'm getting is transmission related and bank 1 pre cat O2 sensor which isn't reading in live data. Tried fiddling the throttle body screws today and it ramped up the idle to around 3000, at certain points it hunts. i've not seen anything in live data for BM+ but its got 12v going to it. The most difference we saw was when the maf was connected but separated from the inlets flexy section.

I dont know how to track the aps and tps yet.

 

[gloverman]

Playing with the throttle body screws is a bad idea. These are factory set and should never be adjusted. What happens when you unplug the throttle motor? Have you confirmed the throttle plate opens fully? Do this with the engine off. Have you also checked there is no external air entering the intake manifold? such as through the power steer idle up circuit? Or leaking brake booster , gaskets, PCV circuit etc

 

[Antanas]

Unplugging any of the throttle body connectors forced the idle to go up.

There is no vacuum leak, you need a lot of air to get to 3000rpm+ and there was no change to anything when spraying cold start spray everywhere.

The throttle body opens fully.

Power steering circuit is connected straight from the manifold to the resonator box. There is no leak from the brake booster, no difference is made even if you disconnect the booster and block the pipe.

 

[gloverman]

Maybe try blocking the powersteer idle up circuit. Connecting directly between the manifold and resonator box is incorrect.

After that if your mechanical side is correct then you might have a wiring issue.

 

[eicca]

The fact that the timing jumps right to 35 degrees advance tells me the ECU thinks the throttle is open for some reason.

When in neutral the normal behavior is to advance timing up to 45 degrees at 2500rpm and hold it there all the way to redline.

Can you read live throttle position and calculated load?

 

[Antanas]

I can read live throttle position, not calculated load. I'll compare it to a standard LS400 and get back to you