1JZ hunting between 2000rpm and 3000rpm when driving along HELP!

[88cameron88]

OK, so the story goes, last week my 1j just stalled going down the freeway, then when i restarted it it would hunt on idle and then come good for a few seconds then start hunting again. replaced throttle body, replaced throttle position sensor, replaced idle control motor.
car was "fixed"

now the issue is, when driving at any constant speed where the revs sit between 2k rpm and 3k rpm the engine hunts. so the car is constantly on and off the throttle, jerking the car back and forward, except my foot isnt moving on the accelerator!!! it makes the car near impossible to drive!
this happens when you try to do any constant speed between 0 and 100km/h, after that your revs are above 3k rpm and it wont do it.'

anyone had this issue before that can offer some sort of resolution for it??


thanks in advance

Cameron

[midnight_purple_GA70]

100% standard 1jz?
standard ecu?
factory fitted?

leaking ecu caps?
fuel pressure

how long since a fuel filter change?

[88cameron88]

100% stock except for exhaust and front mount, engine is fitted in an r32 skyline. fuel filter only has 500kms on it. has heaps of fuel pressure and the ecu has been swapped a number of times with another one and it doesnt change it.

doesnt seem to be a fuel issue... more sensor related or air leak related....

but im asking because it has me stumped now

[EldarO]

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fucked ecu.

replace the ecu, or replace the caps inside it.

[wilbo666]

Have you checked the adjustment of the tps? If the idle contacts are closed above about 2000 rpm the engine ecu will enter fuel cut... Something to check

Cheers
Wilbo

[88cameron88]

read above about allready swapping ecus and not fixing the issue.

[88cameron88]

and thanks wilbo, i have thought all along it was a tps adjustment issue, but have had everyone telling me it isnt,
so i will properly check the tps adjustment and go from there.
thanks

[EldarO]

read above about allready swapping ecus and not fixing the issue.

I did, but the basic thing is, it was fine, and now its fucked, 1jz's are generally built incredibly well, their only real weak points are the standard turbos, and leaky caps in the ecu. My bet is, your ecu is fucked, and when it went, it took something else out with it.

[SHEPPO3930]

This is a long shot, but if it's surging at light loads with little throttle, it may be running lean. I've experienced this in the past (not a 1jz tho). After all other avenues were exhausted, I cracked the sh1ts and threw it on the dyno and replicated the conditions (in my case, 100km/h, top gear, cruising with very little TPS). Hey presto, under these conditions the motor was crazy lean! After re-mapping the fuel table in that area, the AFR's richened up to where they should be, the surging went away.

I'm not saying this is your problem, but it may be something to check!

[88cameron88]

will do, thanks sheppo

[88cameron88]

the ecu was swapped at the same time as the tps, and the problem wasnt solved, only thing is i didnt set the tps, i just put it on, so hopefully this is the issue.

oh and off topic... standard turbos are not a weakness on a 1jz if you put decent dumps on them to keep them cool like any turbo should be.

[George]

I have had similar problems with some other engine type, and it was ignition.
In my case, igniter just entered its road to hell but still ran. At constant speed your AFR normally is reasonably lean. With some ignition system part a bit stuffed, that may cause misfiring because with leaner afr, arcing voltage is higher - it makes spark harder to occur

I would recommend to check some simple things
1 Check for oil on high voltage wires and coil packs, wipe with white spirit if necessary
2 Remove rubber caps from coil packs (on the side that connects to spark plug) and inspect for crack. If you see any cracks this is it. You may temporary fix em with epoxy glue. Even smallest cracks can cause problems
3 Maybe lend 100% good coil packs and wires for an hour somewhere

[manny]

I second Wilbo's advice - I had identical symptoms on a 1JZ Soarer where someone had played with the TPS position and idle screw.
Returning the TPS to the correct position resolved the symptoms.
These settings are 2JZ based but work just fine to get a 1JZ back in order
http://wilbo666.pbworks.com/f/131607...S+Settings.pdf

[88cameron88]

i solved this, thanks for all assistance, i just turned the tps clockwise a bit and its all good!