Strange Idle Issues *Dies At Lights&

[pocket-rocket]

By mal adjusted throttle, your talking the TPS? I didnt look very closely at that.

I think he is talking about throttle plates that someone had messed with despite warnings on the car and in the manual not to mess with them. I don't have a scientific way of doing it, but when I have to adjust one I turn it a bit past the point where the throttle plate no longer sticks after letting it slam shut by way of the spring from a WOT position, that way it won't stick closed down the road.

I wouldnt suspect a sticking IACV simply because pulling a vacuum line off raises the idle up, not drops it. And I wouldnt put much money on it sticking closed, since closed is where I want it to be when it gets warmed up.

I am looking for something that will drop idle speed, not raise it.

That's because you are letting unmetered air past the IAC and TB.

When I get some time I can throw my meter on the TPS and see how linear it is, and what base idle is set at. I really wont be expecting to see much. But may as well try it anyway.

That's not a bad idea at all and can't hurt anything.

[Stinky_1]

the biggest problem I am having right now is that the symptoms have not come back since I put the tranny treatment in the car. I dont want to do a bunch of things at once. If I do, then I will not know what fixed it. If I do it one at a time, then I can say exactly what fixed my problem, so it may help others.

I was playing with the throttle cable to check if it gets stuck at all. It was smooth all the way through.

NNot sure on the unmetered air comment. This car has an Intake Air Temp sensor, not a maf. So opening another vacuum line would do the same thing as the iacv opening. Unless I am missing something.

For now though I wont be changing anything just waiting for the problem to come back, so I can start working through all the things suggested above. I like the tapping the ECU idea. I have seen my skyline run really bad when it had a bit of a weak connection to the ecu. Similar in fact to how this car runs when it is running rough. So, its very possible that one of the connectors is just loose.

I will check the coolant though, and the TPS. And then re-check the throttle plate thing.

I still think this is either a sensor issue, or a connection issue, or an ignition issue.

I dont think its anything to do with fueling, or with air entering the engine. Just the way it stutters, its certainly spark related.

[pocket-rocket]

Vacuum lines are behind the TB, so if you remove a vacuum line with the engine running you are letting air in that hasn't gone past the TB and IAC, so it's air that's not being controlled by the throttle plate or IAC at all- unmetered. Since the throttle plate and IAC can't control this air and it's basically a leak, it causes your idle to raise because there is nothing limiting it except the size of the vacuum port it goes to. That's what I meant by unmetered air. MAF cars still have an IAT sensor too

[Stinky_1]

gotcha,

The good news I suppose is that the problem came back today.

So all my tests so far have NOT fixed it.

I have double checked the throttle linkage, no sticking at all on the plates
I checked the coolant, and didnt have more than a 10th of a volt to ground
I tried tapping on the ECU with the end of my socket wrench and had no change
I tried playing with the connections to the ecu, unplugging and plugging back in to see what happens

So, after the engine cools I will pull the IACV out and try cleaning it up. See if its plugged or jammed or any of that fun stuff, then report my findings.

Anyone else have any other ideas?

I wont be getting any fuel trim readings any time soon, since I dont have a way to monitor that.

[Stinky_1]

So, I pulled the iacv (or what I think is the iacv) out, had a look at it. Nothing much to see. Just a plunger with a spring and an o ring on it. Blew some air through the hole. Nothing really to see there.

I pulled the intake tube off and had a look around. The whole thing around the IACV is nice and clean.

Opened the throttle plate and had a look in there. There is a bit of carbon buildup, but I have seen much worse on engines that still run fine. It is actually one of the cleanest looking intake manifolds I have seen in a while.

I do see what you mean about the throttle sticking though. After me messing around with it, I had adjusted it down too much, so it was sticking closed. I adjusted it to the point where it just did not stick, and closed it all back up. I fail to see how the adjustment on the tb could cause any of the problems listed. It has got me wondering, are you guys thinking the stalling is because of ONLY low idle?

I can assure you, the low idle is caused by something making the ignition not fire right. So, yes, the low idle is making it eventually stall, but that is not the cause, it is a symptom. I am not simply trying to adjust my idle higher, I am trying to figure out what is making it fall. When I dont have the problem it idles at around 750 with a smooth idle. When I do have the problem it will idle at 750 still, but with a lumpy idle.

When it gets really bad, the idle starts to fall to around 500, and then can stall, or just struggle to stay alive. But, I beleive this to be a cause of the bad ignition, not just some vacuum leak somewhere or something like that.

in my search over the engine I came up to the MAP sensor. Or, what I assume is the map sensor. Its on the other end of the engine, towards the firewall? The line that feeds from the front edge of that to along the rear fuel rail didnt look so good. So, When I pull it to see what it was doing it kinda came right out. So, now the car does not start at all unless I really gas it up. It runs rich, and wont hold an idle at all. My new task is to attach that back on. The problem is that I dont know where exactly it went to. So I need to figure out how to pull that manifold off so I can see where it went to, and re-attach it. Anyone have a step by step on that? Is it just the 5 or 6 bolts that I can see sticking out?

[pocket-rocket]

You know, the 92 has an idle issue like that from time to time as well. It will be sitting there all happy, loping and all and all of the sudden it will start to sound like it's falling on it's face and get pretty rough. Sometime's it will catch itself and idle up, but sometimes it won't and will end up dying. It always fires back up with no problems though, and I've never bothered to figure out what is causing it because it doesn't do it too often. Nick (the PO) claimed the Magnecor wires fixed the "phantom stalling" issue the 5 speed cars had, but I think that this is that same problem coming back. I remember hearing about a couple recalls on the LQ1 for stalling and I thought they were fixed with either a new MEMCAL (different programming in the ECM) or fuel injectors.

[Stinky_1]

is that new memcal in any of the newer model Z's? So I could get a replacement by going to a wrecker. Or was it something done much later as a fix for past problems?

When I got the car it never had this problem. After a while it started doing what you say yours does. Then it gets worse and worse. It is still hit and miss though. SO I am not sure exactly how it comes and goes like that. Makes it a lot tougher to trouble shoot

[pocket-rocket]

The way to find out what MEMCAL you have is remove the coolant tank, flip over the ECM, remove the cover and read the BCC off of it. I want to say the latest revision was AYUZ or BCFA off of the top of my head depending on if it's a manual or auto. I hope someone backs me up on this because it's been a long time since I've read the BCCs on MEMCALs.

[Stinky_1]

the memcal number on the actual eprom is BHAK 1619 4256

Has anyone got a dump of the newest one for an auto? If so I could just burn my own. I have an eprom burner and a ton of eproms.

Just got the car all back together again. It starts again, but still has the missfire. I just pulled the ecu to have a closer look, and be certain the connections are good. Hopefully that has a result. But not holding my breathe.

I am open to any other ideas now.

[Stinky_1]

So, the trouble shooting process is on hold again.....

I pulled the EGR valve off, and made a blank plate for it, then put it back on. Now the car starts and idles just fine. Did the blank plate fix it? I have no idea. I will drive it like this and see if the problem comes back. Everything else I tried today I started the car after and the problem was always there. So I know none of the other things fixed it. Ill let you guys know if the problem comes back with that blank plate on.

[bszopi]

EGR was something I was thinking about, but never mentioned. How was the EGR passage? Was it pretty dirty with any buildup inside? What about the EGR itself?

[Stinky_1]

EGR itself looked as good as an EGR goes. Black on the passageways but no chunks of carbon that I have seen on other vehicles. I threw some compressed air down it to make sure all was well, didnt feel any blockages.

The line coming up from the exhaust looked the same as well.

I took a look at the plungers on the valve itself and all of them appeared to be shut tight. I have seen them get tiny chunks of stuff stuck under them before, and even though they looked closed, they still leaked enough to cause problems. I was kinda wondering about that thing, but figured unplugging it would be the same thing. I suppose if it was stuck open, unplugging it wouldnt make any difference at all.

Either way, it seems to be much smoother now. If this works I will need to make a better blank plate. For now I just cut a Sprite can, folded it over itself and screwed the EGR back onto it to seal it all up. Will run it like that for a bit and see what happens. If it doesnt come back, then in a couple weeks Ill make a template and make an actual plate at work. I have done this before on a different vehicle, I always leave the egr in place, that way I dont get any codes on the computer.

Like I say, I will report my findings.