Friends. Seeking for help with my 1993 SC400 / Soarer 4.0L, Automatic gearbox, equipped with first revision of 1uz-fe Car was standing for last 7 years, later we begun restoration process.

-- the issue

The car always running low rpm, below 650-700. Actually in idle (P or N) the car is about 500 rpm, when shifting into gear, the rpm drops to about 300-400, but the car still runs good, has power, throws tail, drifting no problem at all. When AC is on, rpm drops even lower. Sometimes reaching as much as 100-150rpm. ONLY with AC switched on, the car periodically shaking hard, similar to somebody kicking the car on the side. This shaking behaviour may happen once per few seconds, or few times a second, rapidly. Also this occurs only when the vehicle is warmed up, in closed loop... Strange thing

-- whats done...

Plugs Cables IAC valve cleaned and confirmed proper workability by giving voltage to s1-s4 and s4-s1 connectors, resistance confirmed as well. EGR valve cleaned and confirmed workability following factory manual. Throttle body is cleaned Throttle position sensor is replaced and calibrated by the book to align with all the parameters. Timing is done with water pump Water temp sensors replaced. Fan, ecu and gauge sensors. New PCV valve

-- whats not done

Hoses(arrived) Caps and rotors Coil packs(on their way)

--- error codes

21 - left (driver side) main oxygen sensor 25 - running lean I believe both codes related to clogged catalytic convertors which is going to be cut next week as well.

Any help, advice what to look at greatly appreciated.

  • 1
    Welcome to this Stack. The 93, being an OBDI car, won't have after cat O2 sensors, so your codes will have nothing to do with the cats. If the car runs fine above idle and can do the things as you stated, I doubt your cats are clogged (clogged cats absolutely kills performance, but don't usually affect idle quality). Can you get any live data on the car? I'm also wondering about the RPM levels you've stated. Unless your engine is a Wärtsilä, I've never seen any car engine run at those lower RPM levels you're talking about. Wondering if the tachometer may be off? – Pᴀᴜʟsᴛᴇʀ2 Jul 19 '17 at 21:55
  • Perhaps tach is off, will try to get live data snapshot this friday. This obd1 has pre and post cat co2 sensors. My cats clogged and already broke into pipes😅 will cut all 3 of them upcoming sunday – Valentin Rusk Jul 19 '17 at 22:01
  • 1
    Recheck that code 24, it should be for the ECT sensor circuit. If the convertors were truly clogged, I doubt you'd be able to drive the car at any meaningful speed. Is the compressor clutch short cycling? You might want to check and see if the compressor clutch is dragging down the engine speed. – Ben Jul 19 '17 at 22:46
  • Hey, Ben, thanks for response. Compressor clutch or compressor speed sensor are 2 points i am going to check in very close future. EDIT: ect replaced 2 weeks ago with brand new oem. :( all of coolant temp sensors replaced. For ecu, for gauge and for hyndraulic fan.... And, sorry, the code is 25, running lean. Fixed in the above post. – Valentin Rusk Jul 19 '17 at 23:03
  • There is an update, the car runs at about 400 rpm and it feels like trying to die, this is when i feel the shake. In this moment rpm drops very low so that even lights going almost off, then it catches back and idling... And this behavior repeats sometimes a few times a second, sometimes once per few seconds, but not leaving me... – Valentin Rusk Jul 20 '17 at 12:17

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