Lexus V8 idle probs

[mick08]

My lexus 1uz-fe in my hilux is playing up, its been a good reliable car for nearly a year now since the conversion but has all of a sudden started to idle funny, it did this some months ago for a few weeks and then seemed to fix itself, just the last few days it has come back. It has lost its fast idle at 1000rpm when cold and if your not careful it will stall when ya back off. I have looked at the IACvalve, removed it and cleaned it i even replaced one of the roller bearings and regreased the insides but this was not the problem, it seemed in good order anyway, but after reading some other posts on the subject it seems that the ECU temp sensor can also do a similar thing when it gets old and inaccurate it can send the wrong voltage to the ECU telling it that its already warmed up and doesn't need fast idle. This is where i was at yesterday ready to get a new sensor $37 from Bursons or $71 genuine but this morning it did somthing else when i started it cold at 7:00, it idle up to high, it went straight to 1500rpm which it has never done before and it stayed there for a good 10-15min of driving before reverting back to the normal 650 idle, sarvo after work started it up and it had the low idle again. My question is can the ECU temp sensor cause it to idle up to 1500rpm or should i be looking elsewhere? The O2 sensors were both replaced at the time of conversion so are 9-10mths old max, they were aftermarket ones but haven't caused any dramas as yet, someone else on here is using them also and has had no faults.

[stradlater]

My guess is it probably could...

That said, all the stuff I have is aftermarket.

For what it's worth, wouldn't it be worthwhile replacing?

[stradlater]

My guess is it probably could...

That said, all the stuff I have is aftermarket.

For what it's worth, wouldn't it be worthwhile replacing?

[mick08]

True True, i'll do that and see what happens.

[stradlater]

Hell, i have about 5 of the things, all used, but if it all goes pear shaped for you..

[MWP]

Yep, i would be checking both the coolant and air intake temp sensor values.
There are tables in Toyota service docs that show what values they should be for a specific temp.

[punkture]

I wouldve thought your coolant temp sensor (ecu temp sensor) affected the air/fuel ratio mostly, but in turn i guess it could also make it run higher idle? try letting it idle, and as it says in the bgb, disconnect the iscv connector, the revs should jump to 1200rpm, then reconnect it, and they should fall, if not your iscv is dead. ecu codes?

[mick08]

Well i put a new (aftermarket) ECU temp sensor in and it made no difference after i disconnected the battery to clear the codes if any. I did not hook up the diag plug inside the cabin but do have the one on the engine, and i must admit i have not checked the codes. While i had all the covers off i thought i would check out the iscv and it was quite clean inside since the last clean with just a bit of black soot that wiped right off. I did try to cycle the key with the valve out and expected to see it move,it didn't,so i earthed it to the engine and tried again but it didn't move, so i put it all back together and started it up and it didn't idle at all, thinking it had logged a code because i had the plug off the iscv i again disconnected the batt feed to clear codes and it started and idled perfect at 1000rpm, BUT..... thismorning it didnt idle up at all and didnt work this arvo either so I'am now looking at the iscv as the problem, does anybody have a spare one? Does anybody know if they are the same as another toyota that would be more likely to be in the wreckers than the 91 soarer that i came out of. Any help greatly appreciated. MICK

[mick08]

Yep, i would be checking both the coolant and air intake temp sensor values.
There are tables in Toyota service docs that show what values they should be for a specific temp.

Does the 1uz have an air intake temp?

[MWP]

Yeah, in the AFM.
But as said above, coolant temp would effect idle speed more than air temp.

[mick08]

MWP what is the other two wire sensor there when you take the covers off, its closer to the centre. The ECU temp sensor is closer to the drivers side then moving to the centre youve got the gauge sender then theres another big two wire plug, what is that?

[stradlater]

Ones ecu, one is dash/guage, other is I dunno. Think it's for the ecu again.

[RA35GT]

Most likely the cold start injector time switch.

[punkture]

yup is the cold start injector switch, i recently checked mine and it was farked..i used one out a camry, had the same connector but i think the heat range is altered slightly, e.g the effective resistance range. i had similar troubles recently with the 3sgte, turned out my rotor button was destroyed, pull ur dizzy off and check that first it sounds exactly like my problems.

[mick08]

Another update today it wouldn't idle at all whilst driving to work and had to start it several times when i wasn't fast enough to catch it, When i got to work i turned the key off and restarted the engine and it did what i think is limp-home mode, constantly revving up to 1200 and back again,up down up down, i pulled the plug off the ISCV and started it again and it did the same thing, thinkin it had logged a code i disconnected the batt till lunchtime and went out there and started it again, it did idle but it was back to idleing low but at least some sort of idle, it has always driven as normal and does not hunt or miss a beat while on the run so i do not think it is the rotor buttons, i would imagine that they would show up more under load than at idle and its under load that my engine has always run best, its gotta be that damn ISCV.