lights dimming and odd idle(videos)

[kyser182]

ok so. 93 GS.
everything is stock, recently put in a new alternator and battery. within last 6months anyway. but this problem has been there since i purchased the car.
since we cannot imbed, here is youtube links to what i am discribing

first one is the lights dimming. Dashlights, headlights, radio, basically everything dims when i press the break pedal

http://youtu.be/aNzbMa4tV88

this second one is more elaborate to discribe.
85degree day, sunny and i am driving the car. idle is pretty normal the whole drive
40degree night and i have the heater on, headlights on and rear window defrost.
when i come to a stop, the idle wont come down from 1000-1800 , its random where it decides to stop
once i push in the clutch, put it into first gear and let off the break, this is what the idle does

http://youtu.be/ks4LogCJtTE


sorry for the poor quality, i forgot to put settings back on phone, if you require better i can manage that later =p


what i am really looking for here is directions to start looking, things to check/test or replace
i really appreciate it guys/gals !

[wytbishop]

My first thought is that there is a short circuit somewhere in the brakelight wiring. Bhen you press the brake pedal and everything dims it seems like there is a large draw on the charging system.

Your idle problem could be related, but also could be caused by a number of other things. A common cause of erratic idle is low coolant levels. The Throttle Body is the highest point in the cooling system so when levels are low the flow of coolant through there is not constant and the idle will "hunt".

With the engine running, but COLD, remove the top filler cap on the passenger's side of the engine and fill right to the top. Now leave it off and carefully remove the rad cap. This will allow any air in the radiator to escape. Replace the rad cap when it gets to the top and then fill the engine right to the top again. Make sure the overflow res is filled to the bottom line and your cooling system will be totally full.Drive the car till the engine is warm and see if the idle calms down.

If that doesn't do it, I would check the timing, idle set screw and TPS in that order.

From there it gets dicey.

[Nd4SpdSe]

At idle the alternator isn't the easiest for the alternator to create power. If you have all your accessories running, you could notice the light dimming when you press the brake pedal. A volt meter would help troubleshoot that, see what kind of drop you get.

Another thing that it could be would be a bad ground. With a bad ground, it has to force more electricity through the "pipe" for the source to get the power that it demands. A resistance check between the negative terminals on the bulbs and ground would give you an idea if there's something wrong there. It should say about or less than 1ohm.

The weird idle is because the idle is too high. It starts doing that if your idle is around and above 1500rpms, and once it hits 1500, it drops, and goes again. The higher your idle is, the faster it does it. Considering how slow it is I'm going to say taht your not overly off, but a 1500rpm idle is damn high. Could be a vacuum leak or need a TPS adjustment. I'd start with the TPS adjustment, than work with the idle screw from there. Another trick is to unplug the IAC and see how she acts/reacts.

[wytbishop]

^^^ Good call on grounds. Check all your grounds.

[mitmaks]

First thing I'd do is check how much your alternator is putting out.
I got this gauge and it works pretty good
http://www.harborfreight.com/12-volt-ba ... 66842.html

[OROutdoors]

Hi there. It sounds like your car might have a low-resistance fault. My uncle (an electrcal engineer) introduced these to me a few years ago when trying to debug an electrical issue on a Sentra. I gotta say, I don't fully understand them, but to my defense, they are a bit complex. Nd4SpdSe was alluding to it.

The basics of it is that on an electrical system, there may be low resistance in the system somewhere. Low resistance doesn't show up on an ohm-meter, not continuity tester. It shows up as voltage drop. Test voltage across the terminals of the battery -- the terminals, not the connectors. Now test from the positive connector to the negative terminal. If there is a voltage drop, then there is resistance between the terminal and the connector. See how that works?

Next, test from the other end of the positive cable to the negative terminal - if there is a voltage drop, then there is resistance. By doing this, you may be able to find a section of wiring with low resistace. In the case of my Sentra, the problem was the positive battery cable, only about a half inch up the cable. The battery gasses got under the sheathing and was eating away at the cable. We found that out by seeing the voltage drop. The problem did not show up visibly (the red rubber prevented us from seeing it), and continuity was good, etc.

You can also do this test for the ground side by testing from the positive terminal to various parts of ground. I'd start at the negative connector and then work my way further out. Here's an article on the topic, it may be of some use. If you don't have a DMM, I do, you could stop by on a weekend, and we can troubleshoot. I live in Tigard. Maybe Mark or others could stop by too, if they want.

Eric

http://www.popularmechanics.com/cars/ho ... ce/4314662

[OROutdoors]

Kyser182, what did you find out?

[King58]

Same thing happened to me a couple of weeks ago.
Shortly after my car wouldn't start, swapped the alternator, now i'm running good.

[kyser182]

Unfortunately I've not found out a single thing.
I've gone through the entire engine bay and checked every wire and connection I can get my hands on.

The only thing that causes the lights to dim is pressing on the break pedal.
So it's either the rear lights. Or something to do with the break system. I just put on new tail light assemblies and checked the wires all seemed good. I don't know much of anything about the break system to be able to check things.

The odd idle is definitely mostly bases on electrical load. But it will still happen if I have everything off.
I've ser the tps and idle. Working as intended.
I have a brand new alternator so it better not be that. Lol

[mitmaks]

Sometimes "new" parts from parts stores can be bad, poor rebuild, etc. I'd have it bench tested.
As far as inconsistent idle...its most likely your IAC valve.
I would take off throttle body and clean it really well, including IAC valve. Also check your coolant temp sensor.
I've done above (cleaned IAC and replaced coolant temp sensor) and now my idle is consistent and stays where it's supposed to be at ~650rpm.

[OROutdoors]

The only thing that causes the lights to dim is pressing on the break pedal.
So it's either the rear lights. Or something to do with the break system. I just put on new tail light assemblies and checked the wires all seemed good. I don't know much of anything about the break system to be able to check things.

Questions for you:
If you remove the rear lightbulbs does this still happen?
What if you trigger the brake pedal sensor without depressing the pedal?

I assume the car is a manual, not an automatic transmission. Please correct me if wrong.

[kyser182]

Yes it is a manual. I will test a few more things when I can.