Hi guys, i got a 90 ls400 and when i start the car in the mornings it takes about 3 seconds of cranking for it to start and when it does it stumbles for a couple seconds and then idles at around 1700-1800 rpm. If i dont crank it for the full 3 seconds and then try again it starts pretty much instantly and idles around 1800 rpm aswell. I was wondering if this idle speed is normal for cold starts cuz when it warms up it drops to 500-600rpm. It seems really high and probably 800rpm too much. It doesnt drop down if i touch the throttle a bit. Anything i can do to change the cold start idle speed or even fix the cranking when its cold? Must say i need to service the car cuz i recently bought it so who knows whats been done. Thanx
Cold Start Idle
- Thread starter boss351c
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Matt Skinner
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Most modern engines automatically run at fast idle and enrich the mixture when its cold, its the modern version of a choke.
1800 does sound high to me, but I can't claim to be an expert on these engines.
1800 does sound high to me, but I can't claim to be an expert on these engines.
Peewee
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Cranking when cold could be a number of things.
From poor spark to poor fuel pump.
There is a diagnostics box on the front of the motor, put a bridge between +B and FP.
As soon as you turn the key to ON, the fuel pump will start.
Let it sit for 3-5secs, then try the cold start.
If it starts almost instantly, your problem is more likely fuel related (bad pump, dirty injectors, bad fuel pump relay, things of that nature).
If the problem is still there, its most likely spark related (old plugs, old leads)
I'm not sure how long you intend keeping the car for, or how much you want to spend on it, but a FULL service top to bottom will be in the $1,300AUD range.
But we are talking plugs, leads, dizzys, rotors, belt, timing belt, timing belt bearings, water pump, coolant, oil, filters. But most of that is a once in 5 years type service.
As for the idle, on the front of the intake plenum is the ISCV - Idle Speed Control Valve.
Remove it (3 screws, could be a bit tight/rusty), and clean the plunger with carby cleaner. Clean the surface the plunger mates with too.
That should get the idle back to normal.
If there is still a high idle, then you probably have a small intake leak somewhere after the AFM.
From poor spark to poor fuel pump.
There is a diagnostics box on the front of the motor, put a bridge between +B and FP.
As soon as you turn the key to ON, the fuel pump will start.
Let it sit for 3-5secs, then try the cold start.
If it starts almost instantly, your problem is more likely fuel related (bad pump, dirty injectors, bad fuel pump relay, things of that nature).
If the problem is still there, its most likely spark related (old plugs, old leads)
I'm not sure how long you intend keeping the car for, or how much you want to spend on it, but a FULL service top to bottom will be in the $1,300AUD range.
But we are talking plugs, leads, dizzys, rotors, belt, timing belt, timing belt bearings, water pump, coolant, oil, filters. But most of that is a once in 5 years type service.
As for the idle, on the front of the intake plenum is the ISCV - Idle Speed Control Valve.
Remove it (3 screws, could be a bit tight/rusty), and clean the plunger with carby cleaner. Clean the surface the plunger mates with too.
That should get the idle back to normal.
If there is still a high idle, then you probably have a small intake leak somewhere after the AFM.
twisty_toy94
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- Sunshine Coast, QLD, Aust.
Mine does exactly the same boss......I've just never bothered trying to fix it........I have checked for small intake leaks, but couldn't find anything....But I'll check out the ISCV now I know it can get sticky....
Mine also idles rough at times....which I also haven't looked into...
Mine also idles rough at times....which I also haven't looked into...
thanx alot guys for ur input and i did a bit of asking around and someone told me that the starting issue when cold (not the high idle when cold ) could be leaky injectors..I plan on doin a sevice on the car very soon and will get back to u with results.
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