Fluctuating Idle

[phobos]

s13 ka24de + aftermarket cams (don't know which but they aren't too racey) + dc headers. Positive it's not the original motor....

Timing is adjusted, to factory.

Cleaned IACV and TPS with some intake cleaner, well a lot of cleaner..lol

No vacuum leaks as FAR AS I CAN TELL...:(

Do have suspicion of a faulty injector but i am not sure: the car sounds like its misses or "stumbles" every 5 seconds or so... But it isnt really bad and I have always thought it might be a small backfire due to the cams? Iunno... Take this metaphor for example on how the exhaust is: Your washing you car and the water is on full blast but then someone 'runs' over the hose really quick. The water runs and runs then stops for a split second and keeps on going...this happens about every 5 seconds. (LOL can I get any more descriptive?) But there really isn't a "pop" like backfire would make. Maybe it's just because of low rpms=less noise?

Heres the sitution:

Cold start-- idle set below 750; the car dies right when started

Warm start-- idle jumps from 200 to around 900 when I set the idle to around 750-900. It's a consistant up-then-down-then-up etc. movement in the idle, like the ecu stops it from dying and shoots the rpms up but then they fall back down. It's literally like a teeter-totter... When I drive it and after, lets say, i have been going in 4th gear at 3krpm for a while and push the clutch in, it will stall on me if i dont either:

a)downshift to lower speeds and wait for lower rpms before i push the clutch in.

and

b) i obviously keep it alive by heel-toeing it :rofl: and use the e-brake to STOP LOL!!!!

When I set the idle to 1k, it will idle WHATEVER the condition of engine warmth... with no fluctuation. Maybe a little fluctuation within 200 rpms but then immediately idles at 1k.

I also believe the ecu isn't the original ecu that came with the car... maybe from another model? Does this matter? I know some things are different when it comes to putting s14 stuff into an s13, not the other way around though...

Don't know much on the history of the car either. My father got it from an impound auction i believe and is letting me have/use it because my 510 got flamed...:faint:

HELP! Please? According to the manual idle is supposed to be at 650 give or take a few. I dont like running with a 1k idle...

[ryguy]

I know you said you don't think its a vacuum leak but honestly thats what it seems like it is. Look for cracked hoses, I just had a cracked brake booster vacuum hose and i had the same exact problem.

[phobos]

Yeah, im going to check a few more times and have other people look for a vacuum leak as well... Two eyes are better than one! lol and sometimes a second pair of eyes help...

[slider2828]

Get a spray bottle... Make the water really soapy and spray on hoses only not on electrical stuff. It will bubble if you have a leak.... Probably the only way if you don't have a smoke machine or a compressor....

It COULD be also faulty injector.... Ohm your injectors and make sure in spec....

[phobos]

Get a spray bottle... Make the water really soapy and spray on hoses only not on electrical stuff. It will bubble if you have a leak.... Probably the only way if you don't have a smoke machine or a compressor....

That is a very helpful hint! Lol, never thought of that.

[phobos]

Get a spray bottle... Make the water really soapy and spray on hoses only not on electrical stuff. It will bubble if you have a leak.... Probably the only way if you don't have a smoke machine or a compressor....

It COULD be also faulty injector.... Ohm your injectors and make sure in spec....

What exactally is a smoke machine? Like the ones they use at halloween? The Fog machines? Never heard of one.

Where could i find one, and where to you insert the smoke into?

Also, how would i use a compressor to do the job as well?

These seem like better options over soapy water.

[slider2828]

Yes smoke machine like hollywood, but it doesn't come out like a big cloud, but rather the smoke comes through a small tube.... You basically can put it into your intake system and look for where the smoke comes out of it. I dunno if it is water based, but it really smokes it up and look for cracks and leaks. (Shop at my friends school has it.)

Compressor is you take off your intake, cover it up and seal let. Then the big seal, you put a little nipple on it for your compressor and you compression test your entire intake system and vac system. If it don't hold pressure you have a leak and usually you can hear it with a stethoscope.

[Skaterjunky8]

smoke machines burn baby oil. If you cant get a smoke machine which I doubt the soapy water isnt going to do anything unless you can see it get sucked in cause its vacuum not pressure,soapy water is for boost leaks or otherwise pressurized systems like the new California Evap testing. What you need is a good can of 3 dollar brake cleaner. Start to spray it around your intake manifold gasket throttle body and other vacuum lines, and areas, make sure you dont spray it anywhere like the distributor or other ignition source. if you hear the motor idle up then wherever you just prayed is sucking in unmetered air. then isolate the problem. However best way to do it is a smoke machine if your buddies or friendly mechanic have access to one. Otherwise maybe its just your aggressive choice in cams? no CEL?

[Skaterjunky8]

Yes smoke machine like hollywood, but it doesn't come out like a big cloud, but rather the smoke comes through a small tube.... You basically can put it into your intake system and look for where the smoke comes out of it. I dunno if it is water based, but it really smokes it up and look for cracks and leaks. (Shop at my friends school has it.)

Compressor is you take off your intake, cover it up and seal let. Then the big seal, you put a little nipple on it for your compressor and you compression test your entire intake system and vac system. If it don't hold pressure you have a leak and usually you can hear it with a stethoscope.

i dont see how this makes any sense, since your intake valves will never all be sealed at one time. I think you are thinking or a turbo system where you would check the IC and pipes for leaks up to the Throttle body by pumping pressure into the turbine.

[SoguRacing]

i had the same problem on my sr a while back. You're running too rich. if you can, try to lean it out at around 1000-1200 rpm. did it for me. as for cracked vacuum hoses, its a possibility but that would cause it to run lean. more air than measured = lean condition. That was my particular fix yours may be different even though we had similar problems. try it :) good luck

[slider2828]

You do the compressor test with the engine off. Its testing if you have any boost leaks in your system, which can be related to fluctuating idle in terms of unmetered air into your system... Not specifically for anything except boost leaks. Vacuum leaks are just tough in general....

[Skaterjunky8]

hes none turbo, but yes vac leaks can be a bitch if you dont know what your doing

[69datsun510]

I have some good injectors, as you know, so you can switch them out. Nobody posted a common cause for uneven idle can be a bad pressure regulator, but I put a new one on for ya, so it's not that. We had to replace the fuel pressure regulator cause the car wouldn't start, it was flooding out from a bad regulator. If its a vacuum leak, use the brake cleaner spray can, solution. Check the brake canister hose as ryguy suggested, it came off easy and seemed old, I had to remove it to put on the pressure regulator. lmk if you get it solved.

[240_S13]

if you dont find any vacuum leaks then check your air flow meter.

[ConceptS14]

Get a spray bottle... Make the water really soapy and spray on hoses only not on electrical stuff. It will bubble if you have a leak.... Probably the only way if you don't have a smoke machine or a compressor....

It COULD be also faulty injector.... Ohm your injectors and make sure in spec....

a vacuum leak will not make bubbles... think about it.