racepar1

I have been promising for a while to do a write-up on how to fix your wandering/high idle. For many of us we clean the AAC/IACV valves by spraying carb/intake cleaner down the tube to our heart's content but still have a high/irregular idle. The trick to curing this is a ground, but not a ground for any of the idle control valves as they are grounded through their cases. This is a sensor ground. The coolant temp sensor, TPS, one of the switches/sensors under the intake, and probably others share a common ground wire. Over time for whatever reason this ground is no longer enough for the sensors to send consistent and sccurate signals anymore. The solution to this problem is to splice in an extra ground, which sounds easier than it actually is. I have done this to 2 cars with idle problems now and it fixed both of them.

TOOLS REQUIRED
1: razor blade
2: wire cutters
3: wire stripping/crimping tool
4: 10mm wrench
5: soldering iron (reccomended)

SUPPLIES REQUIRED
1: electrical tape
2: blue butt connector
3: blue eyelet connector for a 6mm bolt (10mm head)
4: 3 feet or so of 10 ga wire
5: solder (reccomended)

1: Cut open the harness (as shown in the pics below) and expose the 4-wire ground splice.

2: Cut out the factory crimp connector and strip the wires. Cut it to leave as much length on the wires as possible.

3: Find a length of wire, I would reccomend at least 10 guage, that is a couple feet long and strip it as well.

4: There will be 3 wires on one side and one wire on the other. Twist the 3 wires together (to go on one side of the butt connector). Twist your new ground wire together with the one wire all by itself (to go on the other side of the butt connector).

5: Butt connect the wires using an appropriate crimping tool. This step will be harder than it sounds as you will have to pull the part of the harness that goes to the coolant sensor closer to the rest of the harness to butt connect it.

6: I would HIGHLY reccomend that you solder the wires in the connector for durability and better connection. I really just use the butt connector to hold the wires together so it is easier to solder.

7: There will be some extra length of wire in the harness that goes down to the coolant sensor now as the ground is a bit shorter. Wrap this extra length around the harness and tape the harness back together using the factory insulation.

8: Find an adequate ground point and cut the wire to length. Take it to the chasis (on the strut tower) if your battery is relocated. If your battery is in the stock location then just take it straight to the negative post.

9: Crimp on your eyelet connector and you're ready to go!

Bigsyke

couldnt you just replace the harness's ground upstream before the corrosion? I would just be concerned with ground loops, when 1 circuit is grounded in 2 places. however;

I did the same thing on my Civic and it made a huge difference. What I did was trace the engine harness ground back to all the grounded sensors (ones that werent grounded by the ECU), and loomed them up by location. So instead of 1 ground point with 20ft of wiring, it was 5 ground points with 4ft max of wiring.

Also people seem to forget the importance of the PCV valve. It regulates your idle via vacuum, helps with windage loss, vents pressure through the divider vs venting through the head which unburnt fuel will attach onto the heads surface, thining out the oil (petrol). A clogged valve will contaminate your oil, and blow seals. I change mine every oil change. On the ka's I found its not as easy as a honda.

racepar1

PCV valve has nothing at all to do with the idle, it does however cause seals to start leaking when it goes bad. I wanted to ground the sensors directly and it worked wonderfully. What got me looking in that area is when i tugged on the harness right there the idle changed. I am pretty sure it is not corrosion that causes it I think the factory crimp connector loosens up over time at that particular point. When it loosens up the tar that is around it works it's way into the connection. The ground wire that I added was less than 3 ft long and it takes less than an hour to make the repair.

wiggafly808

Could you be more specific as to which wires?

I'm a little confused by looking at the pic.

Thanks!

racepar1

Once you cut the harness open you will see. It is the only place in that area of the harness where 4 different wires, of the same color (black), are crimped together.

EDacIouSX

i want to give this a try but im just so lazy. out of curiosity... did this fix idle problems when you are at a full stop and are turnign the wheel? cause my idle hops up and down when I turn the wheel (power steering is under load) and when i turn off/on lights it'll idle weird for a few seconds.

racepar1

My car idled weird all the time and it fixed it. If your idle is unstable immediately after a load is placed on the motor a weak ground coulf totally be causing the sensors and idle control devices to respond lazily. Try it, I am pretty certain it will work for you.

Rogue240sx

I did this in all of 15mins, stop being lazy and get out there and do it. The car seems a little better although I'm still having low idle (drops below 500rpm, a little too close to stalling for my liking. when coming to a stop and when i put the A/C on it still revs way too high (1500rpms at idle). Emissions tests show my car to be running rich, after I've cleaned the EGR, replaced the AICV, and installed a new cat for good measure. More trouble shooting for me. Maybe I'll post a new thread to see if anyone has any insight.

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EDacIouSX

i'll give this a go when i feel like moving lol. been so tired from doing other things

racepar1

Try doing an idle adjustment procedure. Let the engine warm up, run it at 2000-2500 RPM for 2 minutes, rev the car and let it return to idle a few times, unplug BOTH tps connections, and adjust the idle via the adjustment screw on the aac/ficd valve block at the back of the intake manifold. That is actually the factory procedure, not something I made up. It is also a good idea to remove the aac/ficd valve block and dissassemble and clean it thoroughly. It was only after I did that that I tried the ground thing.

Rogue240sx

Yeah I've done all of that too. I'm going to be looking into my TPS and other sensors.

*edit* Thanks for your input btw

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Silver96

The pics you used for illustration are of a blacktop sr20 is that right?
The procedure would be slightly different for an s14 ka correct?

Rogue240sx

Looks like it's a KA24DE with a painted valve cover. SR20's look a bit different

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surreybc

tps, iacv, airflow meter, engine temp sensor get their grounds from computer. at least as far as i can tell from the diagram. the engine temp sensors' ground from computer is connected to the tps's ground from computer. obviously, if computer is deciding when things should be grounded you dont want to just hook the wire to a fixed ground. can someone clarify this. it is late. the iacv aac do not ground by being connected to engine chasis, either. i think the ficd is connected to ground, though.


1991 240sx wiring diagram

ImageShack - Hosting :: img0004zx5.jpg

racepar1

Those sensors should have a constant ground, not something that is switched by the computer. If you wanna be sure and don't believe me then do an ohm test with the car off and the key out. If there is continuity to ground then I am right. Just because the wires run to the computer does not mean that the computer is actually controlling it. By adding an external ground the sensors can send more accurate signals and respond faster. The IACV and AAC valves are grounded to the intake mani throught their cases.

surreybc

I wonder why they get ground from the computer and not chasis then. The ones I can think of do have constant ground with ignition off because that is part of the trouble shooting check in fsm.The IACV is controlled by ground impulses from computer so a constant ground would mean it is on constantly. improving the computers ground might help also.

Om1kron

i'll give this a shot this weekend and report my findings.

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Wayne

racepar1

The IACV and AAC valves are not included in the circuit the I added the ground to. I simply grounded the TPS, coolant temp sensor, and exhaust gas sensor directly. All those sensors use constant ground, not a switched or monitored ground circuit. The fact that all those sensors ground circuits are tied together confirms that there is nothing monitored or switched there. If you don't believe me then test it. You seem to be looking for an excuse not to try it rather than looking for a reason to try it.

EDacIouSX

ok so anyways i finally did it and it seemed like it worked.

about 6 months ago I cleaned the IACV with the carb cleaner trick, used a whole can and it helped.

Now, I did what you said to do and it didn't 100% fix the issue but the idle is definitely much more stable. especially when the A/C is on cause sometimes he A/C would idle at 1000 rpm roughly then dip to 600 rpm for 5 or so seconds and then go back up to where it was. Haven't had an issue with that. I didn't use solder so that may explain why the problem isn't 100% gone.

Also, when I was removing the wires and splicing new grounds in i noticed that the old grounds had some corrosion in it.

anyways, idle is pretty darn good now, thanks for the write up!

racepar1

Good to hear!

EDacIouSX

actually a/c did dip the other day down to 600 rpm again and back over 1000.... dont know why. hm oh well

sunnys14

I did this and i didn't see a 4 ground wire splice. Does the ground wire from the CTS connect to the splice? I followed the ground from the CTS to see if it joined any others but I went as far as the 3rd injector and it didnt splice into anything...

racepar1

S-13 or S-14? I have never torn into an s-14 harness to do this before so it might not be there in that harness.

sunnys14

S14 harness, I think they might be different

I just went ahead and spliced in another ground for the TPS and CTS. Sure hope it solves my stumbling problem...

jspec240

Yea buddy!! Great knowledge for the dome... Im installing my KA tomorrow and might use the trick.

Drew

Racepar1

What do you think about meeting me at Magic mountian to check out those sparcos??

LMK

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Addicted2Kouki

How come this STILL isnt in the Archive? good info Aaron.

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PBucch

I am going to give this a shot tonight. I have no vac leaks, I sprayed the iacv like HELL with seafoam aeorosol and carb cleaner, still idling ~1800-2k.

Thanks again for the info buddy.

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initial_drifter

do you know if the ka-e harness is similar? kinda wanna do this too

PBucch

THIS IS IT GUYS.

Giving a good ground here helped me A LOT. my car was idling way high(see above post) and it brought me down to 800rpm. I have some surging issues but I owe racepar for this, my car is actually driveable.

Much love my friend.

sticky or archive this and give the man his due.

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SnakeKack

I don't like ressing things but I tried this and it didn't work. So far i had replaced the alternator with a Nissan Quest alternator. That made my voltage with loads on go from 13.5 to 14.5 which is nice but the idle still dips when there is too much load.

For an example after the car is fully warmed up at night I'm driving and when I come to a stop because my foot is on the brakes and the lights are lit the idle goes down. Or after I stop and let off the brakes it goes back to normal if for an example my window is down and I press the down button again the idle dips the same way.

I've checked my regular battery ground and it's good. The new alternator seems to be doing real good. And I just did the trick in this thread and I have the ground going straight to the negative term.

As far as I know the battery is ok last time I tested it with the car off it was putting out 12.65 volts. Could a bad battery still do this to a car though? I have seen batteries that seem ok but still perform like shit.

Maybe I should look into a grounding kit?