Another funky idle

[benemorius]

1990 240sx 5spd 140-160k milesBored out tb and exhaust chopped off right before the muffler; no other mods that I'm aware of or can recall.

Sorry to post yet another idle problem thread. I'm just sick of searching and sorting and deciding what stuff I need to try and what stuff is irrelevant. I'd appreciate it if someone could ask me the right questions and give me advice that applies to my situation.

This is an occasional problem, and it's done it since my girlfriend got the car almost a year ago. On some trips, my engine will idle nicely at 700rpm or so, but a lot of the time it doesn't like to act right. It will idle normal for about five seconds after I put in the clutch at a red light, but then it slowly creeps up to anywhere from 1000 to 1800, taking about ten seconds to get there. I'll take off normally and the cycle will repeat itself at the next light. Then lets say I arrive at work, and leave for lunch several hours later and it idles beautifully for the rest of the ride.

Well, I say it idles beautifully, but actually it stutters every few seconds while idling at normal speeds (the stuttering is less noticible, if not gone, at higher idle speeds.) I don't know if that is related though.And when I say stuttering, I mean the engine shakes breifly, and the exhaust coughs.

I have, for various reasons, recently done the following:

-replaced oxygen sensor-replaced fuel filter-seafoam down the brake booster hose-seafoam in the gas tank-advanced the timing to +25, which reminds me-

I played with the timing a little and got what I consider noteworthy results. Advancing it ten degrees or so reduced the stuttering to almost nothing, whereas retarding it multiplied it greatly. Advancing it five degrees helped a little, and that's where I left it.

Last-minute note- I would swear that when watching the timing marks, the flash which occurs when the engine stutters shows a degree or two lower than normal. It's like all the marks just shift to the right for a split second and then return to normal.

I'm sure I need to provide more info. Don't get pissy with me; just ask.:asmile

[maik21]

ho yea... i have the same problem with my 240 90 auto trans...when i go to the red light and push the brake.. it still into 850--- then 5 secs it goes to 650.. if i put the gear into neutral... it goes to 1100 rmps.... then 5 secs goes to 850 rpms and if i still into neutral.. then 5 secs and goes 1100 rpms again.. and again, and again and again.....

1100 rpms --- 5 secs --- 850 rpms --- 5secs and again and again...into neutral gear

and into d gear .... 850 rpms - 5 secs -- 650 rpms - 5 secs -- 850 rpms--- again cicle

i replace all the vacum lines... i clean all the sensor arnes (wires) and watch for leaks (weak) i put seafoam trough the fast idle control solenoid.... vacuum hose before throttle body.... seafoam into gas tanks etc.. in other words... i use seafoam to wash the car and the problem still. ...

i think that the problem may be a tps switch because one day ... it have a contact false and it cause that my rpms goes up and down intermitent. but i dont know if that may cause my problem.

i have the idle problem too... the same that you

[benemorius]

Well, add engine grounds to the list. I finally got around to redoing them and I don't notice that it had any effect.

Does anyone have any other suggestions?

[maik21]

today , i put a ground into de aac valve solenoid... the solenoid have 2 wires.. one that have aprox 10volts and other go to the ground that ecu give to it. i cut the wire that ecu give ground to solenoid and i put a ground permanently on it. now, my idle is better. =)) the rev up and the rev down there is no exist =))) im happy ==)

[benemorius]

I disconnected the harness coming off of the tps and it no longer seems to idle high. The stuttering is still there, but the idle speed only bounces between 500 and 800 now. Can anyone tell me what I've done?

[Nismo_Freak]

Start engine, allow it to properly warm up, allow idle to mellow (if possible).

Now you need to unplug the TPS, and re-set timing to about 18 deg. (make sure you run 93 octane or the engine will ping). Now adjust the idle screw on the intake manifold so that the idle RPM is around 800 rpm (650 for MT's but I think thats a little low). Plug in TPS.

See if that smoothes out your idling issue, if not you need to thouroughly clean the throttle body, and the IACV would be a good start as well. After that check your TPS for voltage creep when the RPM's start to rise at idle, also check it for proper voltage at idle.

An FSM would be an excellent tool for you, you can find a copy of the S13 FSM in PDF file around the net. Honestly any of the Nissan FSM's will outline the proper method of diagnosing idling issues as well as ignition timing.

Edit - Didn't notice KA24E... assumed KA24DE

[180fan]

Your SOHC's timing is supposed to be set to 15 BTDC if it's got no other mods. Also check out the fuel injector plugs. Push em around and see what they do. Also check out the plugs for corrosion and being loose. I used some electronics cleaner and a small screw driver to scrape the greenish corrosion off the plugs.

If pulling the plug on the tps smoothed things out though, you may need to check over the voltages for the TPS. The proper voltage readings aren't coming to mind right now but if you check out the fsm it'll tell you the readings.

What Nismo_Freak suggested with the hosing down of your iacv is a good idea. while you're at it, hose down your MAFS and check over the connections there too.

[benemorius]

Hrm. Funny I should happen across this thread. I haven't gotten any email notifications on it recently...:-/

Anyway, I did happen to start messing with the TPS earlier today. The ground appears to be bad. It's reading 1.xxv whereas it should be down around .4v. Tomorrow I'll run a separate ground for it and see what that does. Too bad it's dark out now...

180fan: Are you sure it's 15 degrees? I'm too lazy to look right now but I remember everything I read saying it's 20.

[navysnail]

yes its 15 degrees

[s13sr20chris]

Your SOHC's timing is supposed to be set to 15 BTDC if it's got no other mods. Also check out the fuel injector plugs. Push em around and see what they do. Also check out the plugs for corrosion and being loose. I used some electronics cleaner and a small screw driver to scrape the greenish corrosion off the plugs.

If pulling the plug on the tps smoothed things out though, you may need to check over the voltages for the TPS. The proper voltage readings aren't coming to mind right now but if you check out the fsm it'll tell you the readings.

What Nismo_Freak suggested with the hosing down of your iacv is a good idea. while you're at it, hose down your MAFS and check over the connections there too.

a very good suggestion!