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Hey do I've got a 2006 ZX4 S with a 5 speed and over last winter, I replaced the alternator. Come to this summer, and I've noticed an odd problem. Whenever it is quite warm/hot outside (20+ celsius) and if I get stuck in stop and go traffic, the battery light comes on and the idle drops for an instant to around 250 rpm, as if there is an excess load on the engine. I've measured running voltage (@1500rpm) and its around 13.7-14.1, which is fairly healthy so I don't believe it to be an issue with the alternator. The battery is around 3 years old but gets exposed to -40 temperatures nearly every winter. Also, the idle problem is not constant so I have no reason to suspect a vacuum leak. The car hasn't died yet, so I'm not too worried, especially since this problem hasn't happened when it's cold outside and its about to be winter here, but I really don't wanna be left stranded. Anyone have any ideas?
 

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Check the wiring to the plug on the alternator. Check your air and fiel filter. When was the last time the grounds were cleaned and your spark plugs changed?
 

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Check the wiring to the plug on the alternator. Check your air and fiel filter. When was the last time the grounds were cleaned and your spark plugs changed?
Wiring is fine and I cleaned out the grounds when the alternator was replaced and subsequently when the problem first started. Plugs were changed approximately 30,000km ago.
 

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Check the wiring to the plug on the alternator. Check your air and fiel filter. When was the last time the grounds were cleaned and your spark plugs changed?
Air filter is the odd lifetime filter that they for some reason had, and according to the gauge that is supposed to show its condition, it's still fine. Haven't checked the fuel filter but there aren't really any other signs of anything wrong with the fuel system.
 

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Check the wiring to the plug on the alternator. Check your air and fiel filter. When was the last time the grounds were cleaned and your spark plugs changed?
Air filter is the odd lifetime filter that they for some reason had, and according to the gauge that is supposed to show its condition, it's still fine. Haven't checked the fuel filter but there aren't really any other signs of anything wrong with the fuel system.
Ummm...the low idle symptoms you are describing could be a clogged fuel filter. For the battery light to come on indicates a wiring issue or a bad rebuilt alternator. Why I only buy new alternators not rebuilt. Get a volt meter that plugs into the cigarette lighter socket. That way you can observe the voltage when the battery light comes on. Rebuilt alternators fail when heat soaked due to the rebuilder not replacing all of the diodes. They then can work fine after cooling off.My 06 ZX5 showed green on the gauge even though the filter housing was full of leaves and copious amounts of dust. I removed it and cleaned it out with a shop vac. Car ran much better.
 

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My battery is 5 years old and sees the same kind of temperatures. Haven't had a problem.

Does it happen with the AC on? I know my engine bogs a fair bit when it kicks in, but never as far as making the battery light come on.
 

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Do they teach at schools now that a vacuum leak must be constant? Because it seems to be a widely held idea even though it is whoppingly dead wrong.

If the battery passes a loadtest at the correct CCA then it is good regardless of age.

I'd be looking close at the PCV hose run behind the intake that commonly fails on those, the rubber can react to chemicals to gum up like bubblegum to vacuum leak then reseal to run fine. Seen it more than once.
 

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I was going to say AC too. The AC compressor might be locking up briefly to the point it's stalling the engine (250 rpm) OR the idle isn't getting kicked up to compensate the extra load fast enough, which in either case slows the alternator enough to the point it stops charging the battery momentarily and causes the battery light to illuminate.

Disconnect the on/off wire going to the AC compressor (if like other Ford setups, should be a single wire going to the top area of the compressor, unhook it) and turn the AC on. Will NOT get cold air, but should also not get the engine slowing down to a stall.

If the symptom goes away completely, reconnect the wire to the compressor. With AC on, stand in front of the engine and watch for when the compressor clutch locks up and starts spinning (middle bar on pulley for compressor will either move with pulley when engaged or it won't) as that's when the compressor is actually working. If engine sputters like it going to stall at any point when the compressor clutch kicks on, you'll at least know what's causing the engine slow down.

From there, have to discern if it's the actual compressor, or if the idle speed isn't being adjusted fast enough to compensate for the extra load. Also, IF the cooling system is low on refrigerant, the compressor clutch with cycle on/off constantly like every few seconds. Normally, they kick on/off in further apart intervals as pressure builds/drops.
 

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Haven't had this problem, but I will tell you this about that stupid air filter. I replaced with an after market filter on the end of the stock tube right after the resonator box that has the gauge that doesn't work and let me tell you!! It made a world of difference!! And by doing it this way, when you open the hood, you can not tell there's an after market filter there. So if you put your fender well cover back I would say smog techs won't notice, unless peticulerly nosey. $8 bucks on Amazon and a Gatorade bottle is what i used. Good luck
 
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