Kuroki924

Hey fellow Rennlisters, I have a riddle for you all. So my 82 924 N/A drove just fine all week and I parked it at home Friday night, where it sat until Monday morning. Started up, but the idle was fluctuating (~700-900rpms) whilst running hard, so I shut it off. Started it a few minutes later, and it did the same thing. I didn't drive it for fear of something major being wrong, and today it started up fine again and the idle didn't fluctuate like it did yesterday but it consistently idled too low. (Hovered around 700rpms) again whilst running a little hard, so I got a ride to work today. Does anybody have any idea why this would happen after running completely fine before? (Keep in mind it rained all weekend too, so water may have something to do with it) And what should I do? Should I just let it run for a while and see if it smoothes out?

mel_t_vin

Ignition system could have been adversely affected by rain. How old are the plugs and wires?

Take it for a nice, long, drive to rid the engine compartment of any residual water.

Kuroki924

Thanks for the reply. Since I've had the car I've replaced pretty much the entire ignition system up to the plugs, which I've expected needed to be changed for some time now. Would it be a good idea to drive it with the way it's running?

mel_t_vin

So, all consumable ignition components [plugs, wires, cap, rotor] have been recently replaced?

Water can wreak havoc on electrical components. Is the car only idling low...600-700 rpm? Have you driven it, even just around the block, since it started doing this? Take it out on the road and report back how the engine responds under load.

Kuroki924

Yep, I've even replaced the ignition coil. And yes, that's exactly what it's doing, idling right around there and running a little hard. And I haven't driven it yet but I'm taking it to work today as it's only supposed to rain for about an hour, so I will post updates today. Hopefully my new spark plugs get here today, I'd like to get those changed.

Kuroki924

Well, I was going to take it to work. Believe me, I wanted to. But I started it and it was idling around maybe 500rpms, burning more oil than anything and sounded like it was barely firing, so I'm not driving it like that. It's gonna have to wait until I get home so I have more time to look at and tinker with it. Does this bring any other ideas to mind?

mel_t_vin

Up to the plugs? How old are they? What do they look like?

Kuroki924

Alrighty. So after waiting for parts to show up as well as permitting weather, I've changed the spark plugs. The ones in it weren't destroyed but were definitely due for a change. The car was still running a bit rough so my dad and I adjusted the air-fuel mixture along with the idle speed screw ever so slightly and got it idling steadily at 900-950rpms which is exactly where it needed to be, and wasn't running too rich or lean; it was running beautifully. It drove fine around the block a few times, then began idling around 1000-1100 while softly popping quite often out of the exhaust when I tried to take it to work. I know for a fact that idle speed screw on the throttle body is very easily moved, so could it have maybe spun out ever so slightly from where it was just from vibrations, causing the system's overall adjustment to go out? I don't want to touch the idle mixture because I'm confident it's where it needs to be, and I'm convinced the idle speed screw is where the problem lies now but I won't be able to find out for sure until I get home. Does this bring any ideas into the light?

Kuroki924

Update:
So after a fine adjustment on the fuel mixture the car has been running beautifully again for the past week and a half or so, until the rain came again. Now I know for a fact the engine is in tune, so signs are now pointing only towards electrical components. My first thought is the idle stabilizer on the front driver's side wheel well in the engine bay. I'm going to spend time drying the plugs out assuming there's any kind of moisture in them. Is it possible to relocate that part somewhere else in the engine bay, where it won't get so easily wet? The wires running up to it are fairly long, so I imagine as long as it's safely secured and protected it wouldn't be an issue. I'm thinking about bringing it closer to the firewall on the driver's side, in that little space where the information plate is. As for the ICM that is originally mounted behind the idle stabilizer... Would I be okay fashioning a case to put around that to protect it from getting wet? I imagine that's something that should typically stay dry, and it has to stay where it is on account of the wires it plugs into being fairly short.