1JZGTE revving up & down to 2500RPM on startup

[Jabtronic]

Hey guys, just wondering if anyone knows what could be causing this..

I recently mounted the ECU up behind the glovebox in my 1JZ MX83, and now the engine behaves very different when I start it up. Upon starting the engine it revs straight up to 2.5k RPM then drops and revs back up again continuously so I have to turn it off. It never used to do this before I mounted the ECU (which wasn't mounted yet because I'd just replaced the wiring loom and had it all working fine)

I havn't had a chance to test the ECU in another car yet, but it obviously seems like something has happened to a wire in the loom. All the wires and plugs that I can see look ok..?

Anybody have any ideas what could be causing this? I'll be testing the ECU sometime during the week. BTW this is the 2nd ECU I've had.. the first one that came with the car shit itself months back (engine cranks over, fires up then dies) and the ECU I'm using now is the replacement (which used to work..).

BTW 1JZ is from a JZA70

[Cuzzo]

Usually when the motor does that its air in the cooling system.

So this can mean the wires going to the temp sensor for the ECU, air in the system, or fault temp sensor.

Not sure if this is a symptom of the leaking caps though. Peoples?

[skin]

or a manifold leak but seeing as it was when you moved the ECU im guessing not

[Dimmy]

Usually when the motor does that its air in the cooling system.

So this can mean the wires going to the temp sensor for the ECU, air in the system, or fault temp sensor.

Not sure if this is a symptom of the leaking caps though. Peoples?

I was actually going to say the same thing. Have you changed coolant recently or thermostat etc?

[brett_celicacoupe]

iscv is stuck open.

i could nearly bet $100 on it haha

check for power on the 2 middle pins of the 6 pin ISCV plug. moving the ecu probably disconnected this power supply

[The Real Roadrunner]

iscv is stuck open.

i could nearly bet $100 on it haha

check for power on the 2 middle pins of the 6 pin ISCV plug. moving the ecu probably disconnected this power supply

agreed,

if it is stuck open and you need to move the car just block the hose on the turbo side after it has run around the back of the engine.

[Jabtronic]

Ok guys thanks for the suggestions.. well the ISCV has always acted a bit wierd, I thought it stopped working a while back but lately it seemed to be?. I'll try blocking it off or closing it manually and see if that fixes it.

It's not staying at 2500rpm though, in case that's what you guys are thinking.. it's revving up and then dropping the revs instantly before revving up again, pretty quickly too.

Will also check the coolant, pretty sure it's ok though.

[Gavatron]

From memory, when the ECU is getting the Idle signal from the TPS, and the revs get to a certain point around 2500rpm it fuel cuts. Takai's 2J did it when the wiring was wrong and the ISCV was wide open.

[woggin]

ISCV, we tried to remove it off the jza70 and all it did was rev up and down!!! so we reconnected it, ran smooth again!

[The Real Roadrunner]

It's not staying at 2500rpm though, in case that's what you guys are thinking.. it's revving up and then dropping the revs instantly before revving up again, pretty quickly too.

Will also check the coolant, pretty sure it's ok though.

when the throttle is fully closed the idle switch tells the ECU to go to the idle map (and operate the iscv accordingly) if the iscv is stuck open (or there is another vac leak) then the revs will raise to 2500rpm where it hits a rev limiter (not sure if its fuel or ign or both) then it will drop down accordingly but due the the vac leak it comes straight back up again.

ive been there a few times wth wire ups on various toyotas and if you havn't wired up the iscv it will be fully open as thats the default setting it reverts back to when you switch off the ign.

cheers
linden

PS it wont have anything to do with your coolant levels, that is only on vehichles that run a wax pallet cold start valve ie 4age etc.

[JZX083]

Hey man,
I had exactly the same symptoms on my 1JZ, I swapped ECU's and it went away. I then Replaced the Capacitors in the old ECU plugged it back in and it ran like a dream!!!!!

[xistant]

yeah your ISCV is "hunting" check wiring on ecu since you moved it around, but also check inside for a leaking/swollen Capacitor's.

[Jabtronic]

Ok cheers everyone, last night I tried another ISCV which didn't act any differently. When I block the ISCV the engine runs ok when its warmed up.. (when it's warmed up with the ISCV connected it still hunts/revcuts)
So I grabbed some capacitors from work today and will solder them in tonight. If that still doesn't fix the problem I'll try my ECU in another car. If the ECU is fine then it must be a wiring prob.

Havn't been able to actually check any electrical connections with my multimeter because I broke a multimeter lead the other day lol by leaving it wedged in the door hinge, will replace that today or tomorrow.

[xistant]

dont just soolder in any caps dude

please check your wiring first before doing anything inside, id say its faulty iscv wiring .

[Secks]

not 100% sure if its the same problem ive had with corollas, but there is an easy fix....

having found no documentation quickly, i'll go from memory.. turn ignition off, remove key. open bonnet. Bridge (not 100% sure) te1 and e1. Then start the car, wait 30 secs or so, then remove the paperclip you used to bridge. should have returned to standard. Wish i could find my bloody book though..... pretty sure its like smacking the ecu, and showing it how its supposed to work, then letting it take over when the bridge is removed.

Option B: not sure if this will work, cos you obviously had the ecu unplugged for a while... but anyway... I stole this from toyotanation.com, so meh...
Whenever any engine electrical work is done (moving sensors, making adjustments, etc.) it's always a good idea to reset the ECU. You can do this by either disconnecting the negative terminal from the battery post for a couple minutes (or more depending on how cold the car is), or removing and reinstalling a fuse in the kick panel near the driver's feet. Doing this gives the ECU a chance to forget what it's learned in the past so to speak, and start with a clean slate. If you do this it will seek out fresh readings from all those sensors and use those to make the engine run smoothly, instead of piling the new readings on top of the old bad ones and trying to get a good working operation from the combination.

Cred to Toyotanation, and jeers to my long term memory.

where'd i put my beer.....?