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Discussion Starter · #1 ·
im having problems with idle quality and a little hesitation up to 2000-2500 rpms. when i start the car cold, it jumps to about 1500 rpms for a few seconds (sounds perfect for the first 5 seconds) and goes down from there to die if i dont keep it up with the pedal.

im running the stock 280zxt timing @ 24 degrees btdc. what are you other 3.1 guys running for timing?

on a side note, i was told that the stock knock sensor may hear the louder engine (forged pistons, ld28 crank, etc) and give false alarm. anyone else have any experience with this?

any ideas what i could do to clear up the rough idle and low rpm hesitation?
 

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I just had about the same problem with mine this morning. I had forgotten to clean the old gasket material off the intake face and this caused a huge vacuum leak. The engine wouldn't idle, pull fuel or anything. Nor could it hardly rev up. After removing the gasket and reinstalling the intake, it runs like a dream! So basically it sounds like a vacuum leak to me.

Dave
 

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Discussion Starter · #3 ·
thanks for the reply.

i've checked the vacuum system pretty well. replaced a lot of hoses and verified vacuum levels and functionality by pulling hoses, putting a guage inline, etc. the car won't run with the oil cap off so if there is a vacuum leak, it must be small. after 2000-2500 rpms, it screams and runs smooth with no misses.

i have adjusted the throttle a bit, also.. to raise rpms at idle. this helps to keep the car running at idle but during warm-up the rpms sit around 2000-2500 instead of where they should (around 1500) so i don't think that's the problem.
 

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Are you running a 3.1L stroker turbo with the stock EFI system? Have you adjusted the AFM ect yet?
 

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Discussion Starter · #5 ·
the efi is entirely stock. yes, 3.1 stroker. have not tuned the afm but have verified that it works according to spec.
 

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Discussion Starter · #6 ·
i think the misfire at idle is what's causing the plugs to crap out and causes the hesitation. when i put new plugs in it, it idled a little rough but did not hesitate.

hmm.. could this be caused by a weak spark?

still waiting to hear about suggested timing for the 3.1 using stock efi.. anyone?

thanks guys!
 

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What plugs are you using? Stock timing should work fine.

I can't imagine the stock EFI is going to be able to deal with fueling a 3.1L engine.
 

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Discussion Starter · #8 ·
I'm using the recommended NGK plugs for the L28.
 

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Discussion Starter · #9 ·
i think im going to recheck the cold start, thermotime, head temp sensor and air regulator. something has to be messed up with the idle control system.
 

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There is no cold start or thermo-time on a turbo engine and I can't see how idle speed is going to cause a hesitation. What did the plugs look like that came out, rich, lean? You could easily have a leak somewhere between the throttle housing and the AFM doing this.
 

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Discussion Starter · #11 ·
Ahh.. true. Forgot about cold start and thermotime not being there. Guess it wouldn't have taken long to verify they are working right :)

I think when it idles poorly it is fouling the plugs and then once i get it over 2500 rpms, it cleans them up a little. I'm thinking it's running rich at idle or has a weak spark. i know it has fuel because when it dies you can smell gas. They have a very slight light brown/grey residue on them, but are clean otherwise.
 

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Fuel pressure check time and make sure the regulator isn't leaking into the vacuum line.
 

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Discussion Starter · #13 ·
Fuel pressure is ok. I installed a fuel pressure guage where the clock used to be. I'll check out the regulator.
 

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Discussion Starter · #14 ·
its 37 degrees outside tonight.. im inside my garage which is not insulated but is attached to my house. i got 3.5k ohms. seems like my head temp sensor is ok by that reading.

i took the vacuum tube off of the fpr and notice the inlets were slightly damp with gas. i took the hose off and it smells like gas inside too. do i need to replace the fuel pressure regulator?
 

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Yep, it's leaking and could be the whole problem.
 

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Discussion Starter · #16 ·
well.. new fuel pressure regulator installed. minor difference and it may be because the car sat for a couple days and it's colder outside tonight. during warmup, it almost sounded like it wanted to work right.
it doesnt seem like it's keeping the rpms up high enough for long enough when i first start it cold. started out about 1500rpm as usual.. dropped down to 800 after just 3-5 seconds and then jumped back up to 1500 for a moment and fell to die after that.
really seemed like it wanted to idle there for a few moments and it totally got my hopes up :(
 

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Discussion Starter · #17 ·
i just upped the idle via the linkage. it will at least stay running now but i think there's still something wrong because it misses at idle a bit. i think its rich at idle because you can smell gas. any ideas?

also, i did the air regulator test (pinched the hose while warm) and there was no effect on the idle.

its getting a bit late tonight so i dont want to be running it anymore for tonight. i think im going to plug off the hose going to the brake cylinder tomorrow to see if it's leaking. when i start the car with my foot on the brake pedal it does move but i could swear the power brakes helped a little more while crusing before. the pedal is a bit stiff, especially if i pump it a few times - even while running. stomping on the brakes while idling did make the idle go down a little so it's at least worth ruling out.

i know the vacuum lines on the intake are in good order. i've redone all of them from the vcm, egr, aac, and air regulator. i dont think i've checked any going to the air conditioning yet so i'll do that too.
 

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Discussion Starter · #18 ·
i just checked the 2 vacuum lines going over the engine to the a/c vacuum tank and i'm pretty sure they were backwards. i swapped them. it made no difference. i also tried taking them off one at a time and putting my finger over the holes to see if that helped. when i left my finger off of the smaller one, it was not noticable or did nothing. when i took my finger off of the larger diameter one, it lowered the idle. at least they are on there right now :)
 
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