1jz: unusual high idle on cold-start

[CrUZida]

You do know that you can adjust the TPS?
There are 2 screws on the side that you back off, and then you can rotate it.

But you'd only want a very small region before it goes OC.
You only want it to be continuous when the car is idling.

[bk_]

Tried the car today.

hit 1600 rpm, then ramped downwards within 10 seconds. Pretty cold today aswell so it is an improvement. Also engine didn't feel "sick" (minor skipping) in the first minute of driving, unlike before.

What's the normal initial cold-start idling on the 1jz? Once she stabilizes, it's no problem at all.

CrUZida, I do realize the TPS can be adjusted, although the details about the operation I did not know. Plus I thought if it still has the factory setting stuff still intact, that it's better not to touch it if I don't understand what the change will do, or what to check if incorrectly set. But now I do.

I'm still leaning towards replacing the throttle body with the JZZ30 variant to match the ECU. When I'll do that, I don't know... but I'll report back if I do.

Thanks CrUZida for your input - much appreciated.

-BK.

[CrUZida]

Just because the TPS is in that position now, doesn't mean it hasn't been tapered with since it left the factory.

Some people do random crazy shit.

[ripfast]

i have a 1j in the commodore, and my cold start was workin fine but now it has stopped workin and it just drops to like 600rpm right after it starts, i dont know why, whats the best way to reset computer, my motor was from a jzx81 as well

[bk_]

ripfast,
Resetting ECU can be done two ways:
1) remove ECU fuse
2) remove battery terminal connector.

I hope that's what you were asking. As for how long to wait to put it back in/on... Not sure if the myth is true that the settings still get retained for atleast 30 seconds (nissan forum myth? heh). Doesn't hurt to do 5 minutes?

Hey - since you have the same engine, do you mind checking the TPS pins like I have? Would be interesting to see if the values match with either of my throttle bodies.

-BK.

[mullett]

I'm thinking your O2 sensor is taking a while to warm up. Once the car is warm, so is the 02 sensor, and it all comes good...maybe the ECU doesn't rely on 02 readings straight after it's reset?

RM.

[bk_]

mullett,
hmm... One guy on this forum posted that he doesn't run an O2 sensor... so who knows if he was experiencing an issue like mine. All I know is that the O2 sensor is for emissions reasons (and secondary for fuel economy).

But then again.... some time after (not exactly after. I don't remember) the O2 wire (extended) was affixed properly, the idle issue was gone for a week, but came back out of nowhere.

I could try disconnecting the O2 sensor and see if it changes anything.

fixing the unnoticed tight throttle cable didn't seem to help. :(

-BK.

[bk_]

Just as I had an interesting idea (and went through with it today), I had a closer look at both throttle bodies: both TPS appear to have the same part number, but different color label.

The number below the part number (89452-22080) is slightly different too:
JZX81: 198500-3020 (blue)
JZZ30: 198500-3021 (green)

So I decided to replace the TPS from the JZZ30 onto the JZX81 since it's way much easier than replacing the actual throttle body. Unfortunately that means losing the factory set (pointless argument I have to admit). But on the same token, I took down all the relevent resistance values and measurements :)

Started the engine. Engine revved to ~1300 rpm max (30% more TPS resistance == 1800*(1/1.30) == ~1400... makes sense). and slowly progressed down (!= proper reset). Engine felt like crap when getting boost. Then I realized I did not reset the ECU properly (1 minute is not enough apparently).

Decided to reset ECU again, this time 10+ minutes to make sure. Revved up to a reasonable number then quickly down to 700 rpm (sign of ECU reset? seems to be).

Took the car for a drive, engine response on boost seems much more smooth after 2500 rpm than any time before... instead of the semi-rush of boost @ ~2800-3000rpm. Second "issue": the 6mm or so IDL switch distance was way too much - removing foot from pedal and then applying some of it back felt too sudden/rough about 2000+ rpm, even engaging clutch to make engine rev up felt impossible if I didn't touch pedal. But doing it below 1500 rpm (max) felt ok. Now I understand why you said it has to be minimal, CrUZida :) So adjusted it to be less than before (2.5 mm or so including slack rather than 5-6mm, maybe I should aim for _minimal_!) but did not test again since hammering out in the suburb again would be suss :).

So lets hope replacing the TPS with the matching ECU and adjusting the TPS as per what CrUZida said will solve this once and for all :)

-BK.

[bk_]

Looks like using the correct TPS with the matching ECU solved my problem!

Thanks CrUZida - you hit the nail on the head, it was the TPS indeed I also re-adjusted the TPS so IDL is _minimal_ - it's beautiful now.

It would also explain why my engine was creating so much carbon into the exhaust - engine was basically running lean. ECU thought less air was getting into the engine.

It would explain the following:
- why I had such a relatively low fuel consumption.
- why it felt... sluggish when not on boost - I just thought it was an artifact of no variable valve timing.
- why it was delayed/surging to get power, even when on boost.
- why I had basically no power until after 3k rpm in first gear, even though I had boost.
- why lifting my foot off the accel pedal on boost, it felt... hmm... like it was surging.

I never thought just one sensor would have such an influence over everything :-)

So in summary:
- JZX81 TPS is _NOT INTERCHANGABLE_ with JZZ30 TPS.
- JZZ30 ECU + JZX81 TPS runs lean.
- JZX81 ECU + JZZ30 TPS (eg: non-trc conversion) would run rich I guess.
Random observation:
- ECU reset causes first start to close ICSV.

-BK.

[EvilJack]

im running a jzz30 throttle body and tps in replacement of a jzx81 trc and ecu setup, no problems there i suppose your TPS just wasnt setup properly from the beginning?

[bk_]

EvilJack,
hmm... maybe JZZ30 TPS + JZX81 ecu... the ecu can figure out and adjust to the different (relatively higher) operating ranges of the TPS. Who knows without 3rd party measurements and comparison, heh. But I now know JZX81 TPS + JZZ30 ECU is a no-no.

Back to my original issue... I think the IDL switch needs more leeway... ramped up to 1800 rpm again after reducing IDL switch activation to _minimum_ :( Seemed to be fixed (1300-1400rpm on cold start) when I temporarily had it at 3-5mm... but was horrible to drive.

Oh well... Atleast I know (thanks cruzida!) which thing affects what... that's the main thing. Apart from that, engine runs beaut and better now.

-BK.