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High idle issue ka24de fresh rebuild

876 Views 0 Replies 1 Participant Last post by  Dannovic
Hey guys, I could really use some help regarding my Idle issues on my 1994 ka24de 240sx s13! I bought the car in europe completely pulled apart with rodknock.

After rebuilding the engine, deleting egr and the butterfly valves as well as most unnecessary vacume lines I'm having idle issues. Its not really after I've done this, since I bought the car in pieces and never heard it run before that. (Did the delete because I'm prepping it for a turbo, and most vacume pipes and things were missing)

The problem I'm having is that the car idles really high, say between 1500-1800rpm depending on where the idle screw sits. This does not change at all when its fully warmed up. The car runs and drives great, pulls strong and sounds healthy besides the high idle.

The issue with the high idle is that I can't get it to run right for our emissions and can't get it registered untill it idles right.

So what I've tested and know so far is that the iac stays fully open untill I remove the plug. When i do, you audible hear it close and idle drops to about 1200rpm with the idle screw all the way in.

The air regulator seems to stay open aswell, removing that plug doesn't do anything but I pulled it apart and it seems to be a normally open valve that can close turning one way, or open more turning the other way. But just to test it out I jammed something inbetween the valve so its closed. With the iac connected again and the air regulator jammed shut it also runs about 1100-1200rpm with the idle screw fully in.

If I remove the iac plug with the air regulator still jammed close and the idle screw fully in the motor dies. But with both valves closed and the idle screw out I can get it to run between dying and 1100rpms or so. But it makes a loud sucking noise through the intake running that way, and wont pass emissions.

Not sure if you guys use it, but CO is at around 2% (can only have 0.3) and lambda sits at around 1.2 (however, this number only matters on the second test where you rev it to around 2750rpm. Where its still too high to pass).
If I remove the vacume line of the oem fuel pressure regulator and essentially create a vacume leak CO on idle goes to 0.1-0.2 which is good, but lambda goes way off because theres too much air. So it wont pass the second test. But this is irrelevant since it might be different when the iac and air regulator work properly.

I opened up the iac valve, cleaned it and tightened up the spring as it was a little loose. This didn't work tho.

So some people recommend me to check the tps as thats what the ecu needs to make the idle control valves do their job. So I adjusted it to be at 0.45v when closed and measured the ohms. The ohms however read different than they should be. At closed its 2 ohms, which is fine. But when open it goes down instead of up to 10ohms.

I tested 2 other tps sensors from a ka24e and ca18det and they all read the same. Not sure why, and or of this is correct or not. I swapped the ka24e one in just to be sure, but that didn't help.

I've also changed the 2 wire temperature sensor in the intake, but that didn't help either. Temp on the cluster reads fine.

When I remove the maf plug, I believe it dies. But I'll check that again with all the other plugs installed correctly (iac, air regulator)

When I pinch the hose from the pre throttle body intake to the idle air system it also dies.

The throttle body valve is adjusted properly and doesn't stay open.

Replaced the lambda sensor in the exhaust aswell, but that also didn't change.

Ive also leak down tested the intake with a smoker which shows no leaks.

Anyone have any idea on where to look, what to test or could explain what parameters the ecu needs exactly to make the idle system work properly? As it doesn't seem to change at all between warm or cold. I'm kinda at a loss, and I need it to work on wensday haha. Or atleast, id would be great if it did because if not, ill have to make a new appointment and wait weeks again.

Sorry for the long text, but I wanted to be as clear as possible and show that I've already tried everything I know could be a problem.

Bad ecu? All my spare tps sensors bad? Not sure anymore. Thanks in advance for anyone that can give me some suggestions or help fix the issue! Really appreciate it
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