s14 OBD1 Chasing code 21 and 41, idle and missing issues

[zmannz]

Hey guys, I just picked up another 240sx last night, got a great deal on a clean car and this was the only known issue. It's an auto 95 le? Has power everything, but no sunroof or 5 lugs, 193k and never been modified. So, basically, from a cold start, the car will run fine no matter what until it gets up to temperature. After that, as long as I don't drive it hard it will drive and idle fine, just occasionally it will stumble at idle as if the idle air valve is sticking. I will take that out and clean it up when I can wrench on it more. I know the other issue is something else though. If I have reset the ecu, and then drive it around soft like I said above it will run perfectly 95% of the time. If I drive it hard a couple minutes though, after I come to a stop the first time it will either stall or almost stall out and then the CEL light comes on and it won't idle evenly unless I put it out of gear and play with the throttle a little. Then if I drive it soft its fine again. If I drive it hard more it starts missing under any throttle level and won't idle. Rinse and repeat. I am trying to go through all the intake when Im on it next too, I can see a pretty good crack or two in some of the vac lines and the pcv line from the intake to the front of the head. I checked the timing and it is good. It never has issues with starting. Just put in new plugs too, so I will take them out after a few drives and see if any look different. I am thinking maybe the distributor/coil is going as it is either heat or acceleration related. The guy I bought it from tried a new fuel filter, didn't change anything. Could this be a fuel issue? The codes read out 21=Ignition signal circuit and code 41=Intake air temperature sensor (IAT). I had a a spare new IAT sensor I put in but haven't yet driven it to see if that killed the 41 code. Funny thing 41 only shows when 21 does. I got 20 or so miles last night with no codes then made it throw both just gunning it hard up my street on the way in. Anyway, just casting, seeing if I can fish out the right answer without a lot of grease accumulating under my fingernails. I will update as I am able to try out fixes. Thanks in advance. Oh and before anyone asks, I am going to do the fsm steps when I get back to work on it too.

[compactfean]

Doesn't the harness for the iat and the dizzy come off the same loom? Maybe something up with the wires in that area., other than that you definately have symptoms of the coil going bad. Ive had multiple cars that had coils go bad so I know when they die.lol. Unfortunately the coil is in the dizzy so its rather external coil mod, or new dizzy.

[zmannz]

Word. Yeah they do snake off from the same area. I was fishing around the harness a little last night and found some electrical tape that definitely wasn't factory but I think that a mechanic was only reattaching the harness to a tab that screws to the fan housing to keep it in place. I removed the wire wrap and tape and saw no splices or damage but I can look farther back at the harness when I pull the intake to fix vac and water lines to be sure. I am searching out another distributor to test with, don't wanna buy one til I know its bad because I plan to go external coil or further when I get around to throwing megasquirt on here. I just need this to be a reliable daily driver to commute in while my bimmer is getting painted and rebuilt out back. After that I can tear the motor and harness out or whatever I want.

[zmannz]

Update:

So, I did all the fsm procedures, and everything seemed fine with it there. I did all I knew to do, which was try a new distributor. I also put in an intake air temp sensor I knew was good. I did that and retimed the car, everything ran fine from sunday to yesterday. On the way home from work, I got on the interstate for about 10 miles at around 70mph, and about a mile from my exit the car started running rough under light throttle. It idled fine after I let it coast in neutral for a sec, so I slid it back in gear and accelerated, sped up fine. Then after I go on the exit it started sputtering and missing under light load. Got it home and at every light the idle would jump, almost stall, then come back to normal at every stop. I stopped in at an auto store and got some stuff there, and when I started it up it was fine until I pulled out, then hesitating under light load started again. The check engine light came on again finally and I checked it when I got in, it was 21 and 41 again. I reset the ecu in the evening and test drove it again in some heavy rain. I drove all the way to work and back and it had the same issues but no CEL. Well, this morning I pulled out to go to work and it was hesitating, idle was uneven, and it ran like crap. It stalled in the light before my job and I could barely get it started again. I limped it in to work and pulled the codes again. This time it was only code 21. So, I have replaced all the ignition pieces I can for now. I am starting to think it is a fuel issue. Any ideas?

[zmannz]

UPDATE:

So, I went and played with the car some at lunch. It was back to cold when I opened the hood, I double checked all the wiring and the hoses. All seems right. I started it up and let it idle about 10 minutes until the temp needle started moving. I revved it up a few times, all the way to redline, and then held the revs at 2500 for a good 30 seconds. After it came back down to idle it dipped low and then held fine. After that I revved it again and couldn't get any bad feedback.

Pulled out of the parking lot and slowly made it out of the service road to the main road, and accelerated hard up to 50mph on that road. After I started cruising at 50, the jerking and hesitation started again and for the first time the CEL popped on while at cruise speed. Every other time it has come on while sitting still in gear when the engine dips to nearly stalling out.

It stalled every time I stopped after that until I got to the auto parts house. Revs drop normally then it bogs down, sometimes even the oil light pops on for a sec. I let it sit there for a few minutes while I bought some things and then walked over to grab lunch. After I came back I checked the codes and it came up 21 only again. I started it up without clearing the codes and it idled like crap, as if the Idle control valve was dirty or just not working. I reset the codes and drove it to another parts store where it was parked for almost an hour. After that, I started it up and it idled fine. I dorve it easily back to work, and it didn't start jumping and hesitating again until I was almost back. So, I drove it around the lot some, did some sliding around, hard braking, and hard accel, and it would only jump and hesitate under light load, ran seemingly fine with the gas floored. After that I parked it and it idled nearly fine, but would almost drop out then idle again if I popped the gas a little. Couldn't get another light to come on. I am about to drive home from work so we'll see how it goes again. I bought a nicer meter today that measures ignition dwell and a mass of other things, plus it is way more accurate for dc than the fluke and ideal testers I have from being an electrician. I am going to ohm out and test all the ignition stuff again tonight and clean the iacv. Think I should order a set of injectors or fuel pump to try? I tried unplugging each plug wire while it was idling crappy to see if one didn't make any difference, but they all seemed to make it run worse which tells me all 4 cyls are at least getting a good spark. I have another s14 ecu somewhere in storage, so I am going to dig that up asap and see if its for an AT car. If so I will try that too for s*** and giggles. Any ideas are appreciated. I am almost ready to part my s13 coupe to get a swap for this. I never have issues with swaps like this!