240 WON'T IDLE!!!!!

[matts128]

Bought a 89 240sx with a 98 ka24de swapped into it and it will not idle right for anything and I cannot figure out the issue. iv built many motors and worked on many cars and cannot figure this out, it starts and stays at 2k for a few seconds then drops to 1500 then to 1000 then bounces between 500 and 1k shaking badley and usually after 5 minutes or so of this it stalls it doesn't matter if it is cold or warm. I unplug the iac and it dies, iv sprayed carb cleaner and the idle doesn't pick up and iv replaced the throttle body gasket and unplugging the maf makes the car stall as well so that's not the issue either. I'd appreciate any input before this engine goes to the junk yard.

[centralcoaster33]

That sucks. Flames and Five exclamation marks! I feel your pain.

Idle issues pop up for lot's of people. Have you been searching for similar threads online? I think you're on the right path. Checking vacuum is a great idea. Your ground wires need to be good also. Bad ground and intake leaks will mess up the idle. Carb cleaner is an okay test. Since your into engines, can you get a vacuum pump/ measure tool and check that way?

I have found, with a newer S14 KA24DE that you can run it on either a MAF or a TPS but not with nothing. So, if you unplug MAF and car runs, then TPS is probably good. Likewise if you unplug TPS and car runs, then MAF is probably good.

You have newer engine, did you get newer ECU and all the goodies? Put on a scanner and pull your codes.

Have you checked the voltage of your battery and then alternator? Those need to be about 12.2 and 14.4 volts.

If the exhaust sensors have gone bad, that'll affect your idle and it should throw a code. I've coasted into Autozone with a bad sensor and driven away with a happy car shortly after. They even loaned me a sensor socket and wrench.

Timing. Well, if it won't idle, it's hard to measure this with a light, but maybe try? It's probably bouncing all over the place.

Steady fuel at proper pressure is needed, but I'm thinking you have that. You can check the resistance of your fuel injectors pretty easy and fast. You can listen to your fuel pump.

There's another website with a thread titled "Bogging Issues? Hesitation? Look here." Check that out.

Do not adjust the idle at the throttle body using the screw for the butterfly. You can play with the big screw on the IACV.

You would also have an auxiliary air valve for your AC (I think). So, can you get the car to idle better with the AC turned on? Turning on the AC in the car will make the AACV open during idle. It's a good test. You've plugged your IACV back in by now right? Good.

[matts128]

That sucks. Flames and Five exclamation marks! I feel your pain.

Idle issues pop up for lot's of people. Have you been searching for similar threads online? I think you're on the right path. Checking vacuum is a great idea. Your ground wires need to be good also. Bad ground and intake leaks will mess up the idle. Carb cleaner is an okay test. Since your into engines, can you get a vacuum pump/ measure tool and check that way?

I have found, with a newer S14 KA24DE that you can run it on either a MAF or a TPS but not with nothing. So, if you unplug MAF and car runs, then TPS is probably good. Likewise if you unplug TPS and car runs, then MAF is probably good.

You have newer engine, did you get newer ECU and all the goodies? Put on a scanner and pull your codes.

Have you checked the voltage of your battery and then alternator? Those need to be about 12.2 and 14.4 volts.

If the exhaust sensors have gone bad, that'll affect your idle and it should throw a code. I've coasted into Autozone with a bad sensor and driven away with a happy car shortly after. They even loaned me a sensor socket and wrench.

Timing. Well, if it won't idle, it's hard to measure this with a light, but maybe try? It's probably bouncing all over the place.

Steady fuel at proper pressure is needed, but I'm thinking you have that. You can check the resistance of your fuel injectors pretty easy and fast. You can listen to your fuel pump.

There's another website with a thread titled "Bogging Issues? Hesitation? Look here." Check that out.

Do not adjust the idle at the throttle body using the screw for the butterfly. You can play with the big screw on the IACV.

You would also have an auxiliary air valve for your AC (I think). So, can you get the car to idle better with the AC turned on? Turning on the AC in the car will make the AACV open during idle. It's a good test. You've plugged your IACV back in by now right? Good.

Thank you for the reply, the ecu and goodies is still obd1 but everything fit and plugged in because I had to buy a new ecu and wiring harness so I think the last owner did the proper conversions, it has brand new o2 sensor, also I have egr delete as well as p/s and a/c. I don't believe it is vacume due to not having any idle spikes when sprayed, also I can rule out timing because there is no bog/ hesitation on acceleration nor excessive power loss or backfiring. I had considered low compression but it just runs to good besides the idle. I have a 3" straight pipe and it looks a little rich maybe, could that be linked or maybe something in the obd2 engine to obd1 wiring and ecu that was over looked? But all the plugs on the wiring harness fit except for the missing emission plugs? The only thing that I could even think of is my throttle cable is really streched and has alot of slack but idle should be controlled by ecu and not cable from what I have heard

[matts128]

Anybody else have any other potential causes of this?? Still can't get it figured out...

[matts128]

Thought that after months of fighting with the car I would post the solution I found since I have not seen a solid answer to a KA idle problem any where else. It was a bad TPS, put a new one on, set it to its proper voltage and now the cars runs like new!

[SoundEfx]

Thanks for posting the solution for others to find.