1JZ throttle loss

majestic47

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Oct 2, 2018
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#1
Hi guys,

so, I recently bought a 1990 JZA70. Runs great until the engine has been heating up for about 20 minutes, driving on the freeway. Then if I give it much throttle at all, it acts like its hit the rev limit, at about 3-4k rpm. I have to let off the gas in order to get any sort of acceleration to shift to the next gear. Let the car sit, and its fine once it cools back down. I don't even know where to start, especially since the problem only pops up after the engine is hot. There's has an exhaust leak on the uppipe, but that's the only engine related issue that I know of so far.
 

tylerjacobsen85

WVsupradriver
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#2
It could be unburnt fuel popping in the hot exhaust. I would check/change your spark plugs first. But be careful with the coil pack connectors they will shatter like glass If your not careful. If you do break them you can buy just the connectors from toyota and other places online.
 

hvyman

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#3
Check for codes.

Could have cracked coil packs tho. Pretty common.

Plugs are good to change but coils go bad more often.
 

twin2turbo

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#4
As mentioned check for cracks in the each coil pack along the stems. Also you may have blown capacitors within the ECU, this can cause all sorts of strange issues. If its bad enough the acid can eat through the circuit board rendering it unfixable.

Id also check for codes

Look into a knock sensor rewire aswell. The shielding on the original wiring will be heat damaged and worn out. You can rewire them with RG-58 stranded coax cable that you can find any most wiring stores.


Just a few things to check
 
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#5
Changed spark plugs, and the ignition coils don't appear cracked. I got the issue to duplicate yesterday, after getting off the freeway, from going 75mph (120kmh) for about 20 minutes. After I parked, I gave it a little gas, and could watch the RPM's bounce rhythmically. Drove the car again about 20 minutes later in a little slower traffic, for a little longer, and had no issues. I get steady blinks on the check engine light when bridging from TE1 to E1 and starting the car, so no codes.

Is it possible to test the coil packs? I'll obviously want to do it when the problem occurs again. Can I replace just 1 of them? or will I need to replace the whole set?

Thanks for any help.
 
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hvyman

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#6
Pull the blue boots off and check closely.

It will almost look like it’s a plastic mold mark. But really there tiny cracks. There not going to be gaping holes. Just fine cracks.
 

majestic47

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#8
I'm being cheap, but looking to change the coilpacks soon, and also add an adjustable fuel pressure regulator. I changed the fuel filter, since it needed to be done anyway but no fix. Also checked for boost leaks, and I found a tiny one at one of the blow off valves I need to seal off.

The car is still very drivable. The acceleration issue happens worst when I floor it. like my redline moved to around 4,000 rpm. If I dont put the pedal to the floor, its almost like it wants to happen, but doesnt. Hard to take video while driving.

heres a video of what it does in neutral after I experience the acceleration problem. I hold the gas pedal, and the rpm's bounce. let off, and idle is way low. I can duplicate this problem by holding at about 3500 rpm and then letting off slowly.