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Hello, I've recently completed my 95 SC400 manual swap using a 240sx trans. The motor runs great, idles perfectly, and the transmission is amazing for $300. It will go through gears perfectly; However, while driving the motor will tend to drop past idle and die when holding the clutch while rolling to a stop. I've been slowly releasing the pedal while left foot braking to ease it into idle, but I can't always rely on that especially at a sudden stop. Any ideas? I'm thinking the Idle Air Control Valve might not be doing it's job, though I'd rather not waste the money if I need something crazy like an aftermarket ECU. Thank you for any response.
Don't think I've ever seen a 1UZ mated to a manual and using the stock ECU/electronics. So the engine dies when the clutch pedal is pressed? Hmm that seems backwards to what I'd expect. Release bearing is heavily loading the engine?
Can try cleaning the IACV but don't think it does much when the engine is warm and at idle.
Not that it dies when the clutch is press at any time. I can hold it just fine 99% of the time, and pressing the clutch would be taking load off of the motor. It only happens after putting it under load while driving then clutching in, the rpms shoot down faster then the idle can "catch". It has no rev hang at all. I've thought of cleaning it, didn't want to make it worse, though I'll try tomorrow.
Ah that clarifies things. Is possible IACV is not fast enough since it is designed for only the auto transmission? There is low risk in cleaning the valve. You could always rig up a damper that is used on manual transmission Toyota's, it looks like a vacuum pod but isn't simply a plunger that extends, then retracts slowly which allows the engine to rev down smoothy. This was done back in the day when electronics were not as good.
I think cleaning it helped but didn't solve it completely. I annihilated it with throttle cleaner, disconnected the battery for a while too so it might start learning how to deal with it. Of course my inconsistent tachometer decided to not work today so I couldn't watch exactly what was going on. Happened ~30% of the time while repeatedly testing it, though I only drove it home just now on a cool night. I'll see how it deals with a Florida morning. I might find the plunger suggested, not sure where I'd put it. I had an idea of using a recalled hood latch spring from my job on the cruise control bracket to slow it down instead.
Edit: As I'm looking at this picture I realize how easy it would be to just adjust the pedal/throttle cable to idle higher. Good idea?
Last edited by KaedanMTSC; Mar 24, 2023 at 07:28 PM.
Very bad idea don't mess with the throttle stop screw or cable tightness. IACV takes care of idle along with spark timing, fuel trims etc. changing the stop will mess up how the engine idles and runs.
Making a custom bracket for one of those dampers would not be super hard. Hard part is finding one.
I had to read it a few times... Reading is probably not my strong suit.. lol.. anyway.. Did you have similar issues when it was automatic? It sounds like an issue I had, once I would let it "coast" or "idle" to slow down at speed and it would just die. Whole dashboard would light up at 40mph, but as soon as I hit the throttle it would "come back to life"... Any chance your cooling system is not completely sealed? This may be irrelevant, but may help. Check your radiator for leaks, hoses and cap. If you're having a surge idle, it may also assist here.
Following this. I desperately need to manual swap my '95 SC 400. I had a KA24 transmission, but sold it off back in 2021, figuring I wasn't going to do it anytime soon. Skip forward to now, and the car hasn't been touched.
Out of curiosity, what are the RPM"s at 65MPH? How about at 80MPH?
I don't know if this is going to help, but whenever my manual transmission cars did this, it was 100% because of bad alternators. Same thing happens to my automatic trans cars when I am driving and then put them in neutral to coast up to lights and such.
I monitor battery voltage and I can see it drop below 12, which causes the entire engine to die. But on manual cars if I let off the clutch the engine immediately restarts and its like nothing happened at all. It's a bit different with coasting auto cars, you can put them back in gear but they don't always restart themselves
I don't know if this is going to help, but whenever my manual transmission cars did this, it was 100% because of bad alternators. Same thing happens to my automatic trans cars when I am driving and then put them in neutral to coast up to lights and such.
I monitor battery voltage and I can see it drop below 12, which causes the entire engine to die. But on manual cars if I let off the clutch the engine immediately restarts and its like nothing happened at all. It's a bit different with coasting auto cars, you can put them back in gear but they don't always restart themselves
I see…. Oddly enough this never happened when the car was auto and i used to coast in neutral all the time. Similarly to what Kaedan said, the car holds idle fine too, but sometimes, id push in the clutch to come to a turn or a red light and it’s like the motor can’t catch its own idle.
Once i turn it back on i could coast in neutral just fine.
I usually have to play with the throttle to hold the revs up so it doesn’t die when i push the clutch in.
Usually if i do it correctly, the car gets very close to dying but i catch it by pushing the throttle and thus keeping the engine alive.
It’s almost as the revs drop quicker than what the IACV can calculate. Which is why i need to give it gas to it can hold idle for me…
The dashpot idea seems like it could mitigate this issue, but i’m just curious as to how it was installed or if it fixed the issue completely. hmmmm….
The dashpot is old and needs to be adjusted. there is a screw on it to make it engage earlier to slow down the butterfly. also make sure the cover on the back of the pot didnt fall off it gives the nipple pressure... Giggity
Manual Swapped, Dies When Clutched
