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SC400 a little sluggish/ odd idle

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Old 03-07-18, 12:51 PM
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Slovo
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Default SC400 a little sluggish/ odd idle

Picked up a new to me manual swapped SC400, was S/C by previous owner but now it's NA again. Had a ton of vacuum leaks/most of the systems were taken off for the EFI and had a rotted rear subframe. Replaced everything from the blown HG shell I had sitting here. Now it's running and driving 100x better but still doesn't feel as fast as I think it should and has a weird condition we're it will get caught in a high idle loop like warm up enrichment(1100-1200) no matter what temp it's at. if I turn the car off and back on once it's warmed up it will drop down the regular 600 rpm idle some driving will result in it climbing to 800. I was thinking maybe CLT sensor but there isn't a code. All I got was a 27 & 29 (obd1). That's sub o2's? Don't think they affect the afr at all but may be mistaken. Need some expertise
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Old 03-09-18, 08:24 AM
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Most of the time, Sub Oxygen Sensors monitor the Catalyst efficiency, so I doubt that would be your problem. Older SCs tend to have issues with both the VAC meter and Idle Air Control Valve. Also do not forget, that OBD 1 only sets codes for hard faults (IE: the component has 100% failed). So even if said components are sending bad signals to the ECM, it will not set codes for them. Manual inspection and testing will be needed.
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Old 03-27-18, 04:43 PM
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Got a new IAC in there, found a couple split vac lines. It's a lot better but still only getting 12mpg.
codes are still popping up for 27&29, some say that main o2 some say sub? Does anyone have a definitive answer?
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Old 04-20-18, 12:40 PM
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I got a new maf and tps put on and new the symptoms have gone from it being underpowered to bucking throughout the revrange. I do believe the fuel pump ecu is already bypassed to run the Walbro 255, key on and the pump is running nonstop.
Watching the wideband while it's bucking shows it's going lean.
The bucking feels closest to fuel cut in a turbo car.

Other things to note that that it does smoke a little on cold starts and smells very rich. The car pulls hard when it's cold, hard enough to start breaking the rear loose at the top of first.

Now I'm leaning towards maybe a bad ecu?
any input is appreciated as this problem is super annoying.
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Old 04-25-18, 10:07 AM
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Originally Posted by Slovo View Post
Picked up a new to me manual swapped SC400, was S/C by previous owner but now it's NA again. Had a ton of vacuum leaks/most of the systems were taken off for the EFI and had a rotted rear subframe. Replaced everything from the blown HG shell I had sitting here. Now it's running and driving 100x better but still doesn't feel as fast as I think it should and has a weird condition we're it will get caught in a high idle loop like warm up enrichment(1100-1200) no matter what temp it's at. if I turn the car off and back on once it's warmed up it will drop down the regular 600 rpm idle some driving will result in it climbing to 800. I was thinking maybe CLT sensor but there isn't a code. All I got was a 27 & 29 (obd1). That's sub o2's? Don't think they affect the afr at all but may be mistaken. Need some expertise
i have a 1992 Sc400 and i have similar issues. If i have my windows and sunroof closed on a hot day. Same as what u said. I open windows come back out 30 mins later runs fine. Only does it after sitting in the heat. Idk what it is
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Old 04-25-18, 04:55 PM
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I bought a new clt sensor and it did help the idle.
Then recalibrate the tps with feeler gauges and all.
The car ran worse and got stuck idling at 1200 rpm. I adjusted it by hand again to make the idle drop. Now the car idles steady, no hump at idle and the age is around 16 with rpm at 600. Still bucks under any moderate accel though.

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Old 05-03-18, 04:37 PM
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The problem persists.
some days are better than others, I pulled the codes after I've driven the car for a 100 miles and it came back with 24 and 31 (air meter and iat).
i have 5 laying around here but I know 2 have been tested with a volt meter as working.
Swapped it in and have been driving it around, made a pretty big difference at first but slowly but surely the bucking came back.
Is there a fuse or a way to test and make sure the ecu is getting correct signal from the maf?

this **** is driving me nuts!
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