Idle problems an tuning question

[rbduck]

I have a 1990 240sx with the ka24e SOHC engine. FIrst the question. On the FAQ there are tw procedures listed for tuning the idle via tuning the TPS and IAA.The SOHC procedure gives zero details on the procedure.So, will the DOHC procedure work? I assumed it would so I tried up.

Now for the problem. I followed the procedure closely. The TPS was very linear from 2k ohms to 10 k ohms. At normal running temp, I adjusted the voltaage to .50volts (midway between the .45 to .55 range) . I disconnected the harness to the TPS and reconnected per the procedure.Next, I disconnected the harness again. I adjusted the IAA to 650rpms. When I reconnected, the rpms went up to about 1700 rpms. I took the car for a drive. Every timr I stopped for a stop sign, the RPMs went to 750rpms immediately. When I went home. I pulled into the driveway. Killed the engine and restarted, the rpms went to 1700. My son used th ecar last night. when I talked to him this morning, he said it idled at 1700 most of the time. When I drove it to work this morning and had to stop., It idled at 1700 about two thirds of the time. The other third it would idle at 750.

Oh yea, I've checked ALL the hoses and vacuum hoses. No problem there. Any of you guys have any ideas???

Ruben

[BabyboyDeLa240]

you sure your engine is not cold when you start driving it.... My car idle there when cold but after it warms it drops to around 600-750 and when you apply brake it drops a lil more.

[rbduck]

Yes, I assume it,s hot after doing 20 miles of road driving and when I get off the freeway it will idle 1700 at one stoplight and it might idle 750 the next stoplight. I'm sure it's hot..thanks for the reply

[schyawn]

I have kinda the same problem...The engine idles fast (about 1700) when cold...that's fine...after it warms up, the idle is good as well (about 750). BUT if after i turn the car off (when HOT), and then restart, it idles high again, about 2000, sometimes going up and down between 2200 and 1700. Sounds like i'm revving the engine like an idiot to anyone outside the car. after a minute or so it goes back to normal. Any ideas?

[rbduck]

Sounds real similar to mine, except if I stop at a light and it's buzzing at 1700rpm...it's not gonna drop nomatter how long I sit.

And before anyone asks. The butterfly valve is not sticking and the stop for the manual idle adjustment is correct.

[rbduck]

OK..I'm replying to my own posts now..(talking to myself?) When I was coming home. I cranked my engine and it idled at about 1000rpm. I stopped at (6000 stop lights) 10 stop lights (I counted). At each stop It idled at at around 700rpm.Just before I got home I wondered somthing. here comes another story) My driveway sits at about a 10 degree angle(hood high). When I pulled in and depressed the clutch, BAM 1700 rpm. The reason is that yesterday after tuning it. I drove around, The motor idled at 700rpm at every single stop. WHen I drove into the driveway....you guessed it 1700rpm...

I don't know if this is merely a coincedence or what, but I'm going to watch it closely. This angle thing couldn't possibly have anything to do with it. Surely. I am curious if I were to disconnect my battery overnight to reset the ECU if it would have a positive effect. Any Ideas out there?

[240nismo]

that buzzing is your heat shield, im gonna take mine off, its useless anyways

[rbduck]

LOL..LMAO... I'm sorry,, I was using the word "buzzing" as a figure of speech and not a literal term. I ment the engine was idling at 1700.

Oh, by the way, I took my heat shield off a long time ago.. the buzzing was driving me nuts..

Have a good one..

[rbduck]

ok, I think I'm boring you all to tears. here's what I noticed over the past couple of days . I took the car for a long drive at lunch. The engine idled perfectly until it warms up. then when you stop it drops to around 700 rpm then climbs over the next 10 seconde to 1700rpm... that's it in a nutshell..any ideas??

[240nismo]

vacuum leaks, ignition might need to be advanced, check to see if there are two wires connected to the distributor... one of those is the timing advancement-it ticks the distributor over to give it a constant spark and keep a steady idle. It should be a single wire, the other one is like a bundle of wires.

[rbduck]

Here is what I did to resolve my problem. I removed and cleaned th IAA/AAC valve. I cleaned corroded connections to the AAC valve and the temperature sensor. I put i back together...followed the procedure to set via the TPS and all works perfect now.

I do have one last question though. Why the hell do they put a idle adjustment on the ECU when it actually, at least to me, does absolutely nothing?