High idle & cold start problems

[Project240]

Why the hell is my car idling at 2500RPM?

First of all, it takes about 2-3 minutes and like 15 tries to get it to start in the morning. Then, once it starts, it idles at about 2500RPM. THEN, once I start driving, it keeps idling at 2500RPM, but the idle drops and rises. It'll shoot up to 2500, then drop to like 1300, then up, then down, about every 2 seconds. As if the engine is revving itself. After a few minutes it calms down, but still idles kinda high.

WTF? I don't think my AIC is connected (I know it has something to do with connecting a black/yellow wire, but I'm not sure exactly what to do), so I'm sure that would help. Does anyone know *specifically* which two wires to connect to make the AIC work? Don't say "just use the KA lower harness" because I wired this car almost a year ago using the RB lower, not knowing the KA lower would be easier.

[Andrew85cm]

Yeah ditto. I have the same problem. I was told to connect the black and yellow wire from the dash harness white plug to one on one of the oval plugs so I connected it to a black and yellow I found on a gray plug. My cold start problem was not fixed so I disconnected it. I wish I had used the KA lower harness freakin a. I would really like to know how to get this thing to start like a normal car instead of the 15 tries and me looking like im driving a piece of crap. My car doesn't idle that high though. It did when it was misfiring but it will idle at like 1500 to get warmed up. Once I get driving it drops to about 800-900 rpms. I also have a problem getting into first when my car is super cold. Any info would be awesome.~ANDREW~

[Eikon]

Both situations are very similar to mine. Obviously a common problem for RB swaps.

I have a very hard time starting when cold. I am installing a fuel pressure regulator right now because I think my problem is getting fuel into the rail or cylanders at cold start. I should have it done in a couple days, and I will post if that helps.

JonPowell recommended that I check my signal on the wiring from the ignition to the ECU. He is suggesting that I (we) might not have the ECU on the same page to get the thing started.

Have either of you tried the diagnostic mode on your ECU? What errors if any are you pulling?

As for the high/hunting idle.. I also had this problem. I was advised to remove the Auxiliary Air Contorl unit and clean it very well with Carb cleaner and then reinstall it. It is very easy... sits at the back of the intake manifold.. only four bolts... remove the solenoid and go to town on it. My idle is now very smooth.. You can adjust the idle up or down with the screw on the AAC unit.

Both of you should try cleaning the AAC.. see if that helps.

I will get back to you if I find out that fuel pressure is the cause/solution for the cold starts..

[Andrew85cm]

I have a nismo fpr and that does nothing for me. I am currently running the correct fuel pressure. I'll try cleaning that AAC valve that seems like a good idea. I was thinking that I will see if that works. I'll try this weekend and get back to the forum to tell results. I have reset my ecu but I haven't checked the codes for it. I believe Carl H did for me. I think all that is okay.~ANDREW~

[JonPowell]

Problem #1, sounds like bad MAF...symptoms of bad MAF=Super high idle(around 2500), rough starts, super rich.

Problem #2, sounds like no cold start signal from ignition switch...symptoms of no start signal=Super hard start when cold

If AIC was bad, you probably wouldnt idle at all, the valve is normally close to closed.

[Andrew85cm]

Sorry to sound dumb but where do we connect "cold start signal from ignition switch" to what ever it needs to be connected. I am in western PA and the weather is always freakin cold. I mean negatives and when the car takes 10 hours to start (being sarcastic) its not good. Thanks for the help Powell. You are awesome at that whole wiring thing. This is the reason I am studying mechanical engineering and not electrical. Dang those wires.~ANDREW~

[Wulfgang]

Both situations are very similar to mine. Obviously a common problem for RB swaps.

I believe that this is only a common problem with S13 RB20's. Therefore, it is more likely a wiring problem and NOT a mechanical problem or sensor problem.

[USMCgetsome]

start wire on the ecu plug is #43. John wants you to find the ignition relay and tap it into the 12vdc coil of the relay. Many people have done it. Helps apparently. I've done it as well and i've never had a prob. Starts up cold warm hot whatever temp. Also, the AAC valve has cause issues with idle and startup. But my old rx-7 used to do the same thing it's called pulsing start at 1000-1800 rpm and back down. It would only ilde well when it was really warm. that was when i had overheated my engine and warped my housing.

[Slo_240sx]

I would start with a coolant temp sensor. Check your coolant make sure its full, if its low then pressure test the system and make sure you don't have any leaks. Try disconnecting the coolant temp sensor and see if it changes anything. Sounds like its reading way off colder than what it should be and giving it alot of cold enrichment for a cold start. They when it warms up it probably goes haywire and makes the idle fluctuate. I would also look into checking the tps sensor and making sure its getting the right reading. Just starting with simple stuff even though you guys went hella deep into it. kepp up the good work fellas!

-Alex

[Andrew85cm]

I have a new coolant temperature sensor. I mean the one that goes to the ecu not the gauge cluster. It came broke so I replaced it with one that fit from I think a Z32 but maybe something different. So I don't know if it's something different but I think the engine is reading fine at least on my engine. I haven't got a chance to take a look at anything yet.~ANDREW~

[Yellow4g63]

My cold start problem was because I didn't have the cold start wired to the RB ecu. It's easy to find on the ecu and look in the KA dash plug for the start signal wire. .... well on a S13 anyway not sure about the 14.

[klh6686]

yea i figured out which one on the RB ECU is start signal, but where on the car do i tap from, i couldn't figure it out from the digrams... and before you accuse me of not researching i figured out my speedo, tach , and temp sensors with the rb lower

[accel junky]

Should be the orange wire on the KA white dash plug.

[JonPowell]

yea i figured out which one on the RB ECU is start signal, but where on the car do i tap from, i couldn't figure it out from the digrams... and before you accuse me of not researching i figured out my speedo, tach , and temp sensors with the rb lower

Any +12V that is hot when key is in START ONLY will work. All you need to do is let the ECU know that you are STARTING THE CAR and it will fatten the fuel map & alter the timing a little to make it easier to start. It's like a choke on the older carbeurated cars.

[Eikon]

See Above ^^^^

Thanks Jon!!! You were dead on. My S13 with RB20 starts right up... And that's saying something consider it's below freezing here. The wiring did the trick.

Thanks again!!!

[klh6686]

yep that did the trick, i ran a wire from the orange wire on the plug by the glovebox to pin #43 and i no longer have to tap the gas a little, i just hold it to start for a second or 2 and she fires up . that makes me so happy thanks guys!

BTW, Project240 (thread starter), you should try this out and post back your results, good luck

[Project240]

So this KA white plug, it's up under the dash somewhere? Not coming off the ECU harness? Will it just be hanging free?...

[JonPowell]

It's actually clipped to the metal dash reinforcemebt

[klh6686]

As jon said its clipped to the dash reinforcemnt. It is located on the passenger side right above the ecu, you should be able to get to it by just removing the glove box. If you did like me and put the RB20 tach in the stock gauge cluster, its the same plug that has the wire you tap into for the tach. connect the orange wire to pin #43. Good luck.

[frosted flakes]

i use to have a cold start problem in my s13 with the rb20. it would take forever to start in the cold. but now since i wired it into my s14 its starts soooo easily in the cold. one start and its there. i think you have to check your wiring. the 8-step wiring doesnt show how to wire up the cold start injector. thats where it is right there. wire that up and i guarantee it will run good in the winter from now on. mine does.

[Project240]

Thanks!! I connected the cold start wire and all is well with that

I cleaned the AAC, too, but now my car is doing that stupid revving s*** even worse than it was before. Vacuum leak, maybe?

[JonPowell]

vacuum leak or your cleaner ate one of the seals in the AAC.

the 8-step wiring doesnt show how to wire up the cold start injector.

The VW's used to have a cold start injector, a 5th fuel injector in the intake tract to add addl fuel. The RB has nothing like this, instead it modifies the fuel maps on start up to lengthen the duty cycle on the 6 injectors. I understand what you were saying but the Nissan cars have no actual "cold start injector"

[Project240]

After looking at the seal on the AAC (where the 4 bolts hold it on), that is a very good possibility Think I could use some RTV or something to make a new seal for it? I'd bet it's a ***** to try to find a new one from Nissan...

[Slo_240sx]

like jon said theres no cold start injector. Its called "Cold enrichment" when the ecu senses a cold temp and changes the fuel maps. Open loop when its cold and runs the coolant temp sensor for most of the fuel settings, and after it reaches operating temperatures it switches to closed loop and runs fuel and timing maps off the o2 sensor.

[Project240]

Does anyone think I could just use some RTV sealant where the AAC bolts to the manifold? Or would it be best to buy some Mr. Gasket and trace myself out a gasket??

[RB20FordRanger]

Ok guys I have been looking for a fix for this problem for about 3 months now and came up with nothing. This is the first RB I have ever owned/worked on so I'm new to everything. That being said I put the RB in my 1994 Ford Ranger..... Sooooo I have the same problem with high idle usually about 2300-2500rpm I haven't had a chance to experience cold start as it hasn't dropped below 80* in the last 3 months. When I was doing the swap I had my intake manifold and valve covers Powdercoated. Could having the intake manifold Powdercoated messed something up? Or where is a common spot for a vacuum leak? When wiring I used the factory RB lower harness and ordered a wiring specialties RB20DET to any Datsun harness for the motor and used the stock chassis harness from the ranger. I understand I drive a ford but I have the Nissan where it counts. Any info on the subject of how to fix the high idle is what I'm looking or at the moment. Thanks

[RB20FordRanger]

Project240 I'm pretty sure I used rtv for the AAC on mine and haven't had any leaks there.