Is it possible to wire and ISC valve the wrong way

[Jez England]

Hi All,

I have a 1UZ in a WB ute.
When cold it has a very low idle (600rpm) and hunts a little bit.
When warm it idles very fast (1200) and occasionally seems to have a small miss/studder.
Temp sensor OK.
No engine codes in diagnostics.
So I am wondering if it possible for it to have wired incorrectly during the transplant and whether I can just reverse ISC1 - ISC4.
Thoughts

 

[Jez England]

Update

I ran continuity tests between plug and ecu wires - all appear to be wired in correctly. So I reversed the order anyway at the ECU to see if it would make a difference. It made no difference to the cold idle. Didn't wait to see if it fast idle at operating temp.

I put the wiring back to the original but now I am stumped at what next.

Thoughts

 

[blinkerfluid]

is the M-REL output wired correctly?

IIRC, the ecu uses the MREL to keep itself on even after you turn ignition off to reset the IACV motor. So the next startup it causes fast idle and then slowly comes down to set RPM when at operating temp.

 

[Jez England]

I believe so, Black-Orange wire from ECU E11-4 to Pin 86 on EFI Main Relay and I can hear a relay click several seconds after I turn off the ignition. When starting the engine has a very short period of fast idle and then comes back to a very low RPM, then as the engine warms up the idle goes up to a fast idle. It was like the ECU temp sensor was reversed, so I checked that and it is good. The IAC resistances across the solenoids are good.

 

[blinkerfluid]

I believe so, Black-Orange wire from ECU E11-4 to Pin 86 on EFI Main Relay and I can hear a relay click several seconds after I turn off the ignition. When starting the engine has a very short period of fast idle and then comes back to a very low RPM, then as the engine warms up the idle goes up to a fast idle. It was like the ECU temp sensor was reversed, so I checked that and it is good. The IAC resistances across the solenoids are good.

engine coolant temp sensor good?
Coolant bled properly, ie no air in the cooling system?

if the engine is missing or performing bad / hesitating specially when warm, have you checked and confirmed if there are no vacuum leaks, good ignition system and plugs.

 

[Jez England]

Check the old sensor and replace it with a new one - Check it was with in spec before putting it in.

Ran the engine up to temp so I would have thought all the air was out of the system + plus it does the same behavior every time, idle come up as the temp increases runs about 95deg when operating.

I haven't found a vacuum leak. The engine runs well, but occasionally it sound likes mike it hesitates a bit like it didn't fire properly, but I don't have any codes come up to suggest the ignitor didn't fire.

I just ran the voltage on the OX sesnor and earth in the diangostics and it ranges between 0.1V and 0.8-0.9 so I think they are good as well.

 

[Jez England]

I tried to reverse the ISC1 - ISC4 Pins in the ECU thinking they had been wired wrong in the transplant, but it didn't make a difference, so I put it back the way it was originally

 

[Jez England]

I have an update for anybody interested. IAC bearing was seized, so I replaced them, but it still had the same behavior, idles faster when warmer.

I though the IAC was working previous to this post, but it was not. Now I definitely knew the IAC was working, so I figured it (IAC) must be out of range i.e. the idle stop had been adjusted for cold idle with the IAC was not in the picture. I watched a few You tube videos (thanks Kevin Glover) and spent some time reading the documents I have, and I think I have it.

Looks like the top screw (its on the secondary buttery and I'm not sure what it is called) had been adjusted to compensate for the IAC not working. So the true idle stop (bottom of the primary butterfly was several mm off) and the TPS had been adjusted to suit.

Anyway, I adjust the idle stop back to about 600rpm when the engine was at operating temp. then using the guide given by Kevin Glover and the manuals (had to change it slight given it is the car but basically the same checks but at the ECU using a multimeter rather than a test lamp), I reset the TPS.

Now it seems to idle well when warm (700rpm), will still need to see if it idles OK when cold ... I'm in Western Australia so it will probably be a while until I get a chance to test it

 

[Zuffen]

Well done!

Things like this can be a bitch to track down and the engine is 30 years old so you're always wondering if the ECU is at fault or not.

Kelvin must have saved a heap of people a lot of heart ache! I know he's helped me out.