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Discussion Starter · #1 ·
Recently replaced my t body with excellent results except the idle. In gear at a stop idle speed is 600 rpm, but engine shuttered intermitantly. Put it into nuetral and idle goes up to 650 and engine smooths out.

I was under the impression that you should not adjust the idle adjustment on the t body.

What do I do?
 

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OUT OF BUSINESS / M.I.A
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There's a zillion threads on Idle Adjustment, TPS tuning and IAC Cleaning/Replacement. Grab a six pack and make a night out of it...........
 

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Discussion Starter · #3 ·
I have a full bottle of tequila instead, but its a week night. Should I still break it open?
 

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Recently replaced my t body with excellent results except the idle. In gear at a stop idle speed is 600 rpm, but engine shuttered intermitantly. Put it into nuetral and idle goes up to 650 and engine smooths out.

I was under the impression that you should not adjust the idle adjustment on the t body.

What do I do?
Mine idles at about 550, smoothly. Is there a reason why your's doesn't idle smooth?
 

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Discussion Starter · #6 ·
No idea...never did this before changing t b , but other tb never idled this low. Engine just shakes at 600. rev it up a little and smooth as silk. Ithink its just the shakes from a too low of idle.

From the archives, looks like I need to check for .9v at tps and not mess w the idle screw ,which I kind of remmeber from my 90 5.0 days.

If your s actually idles smooth at 500 (in gear/load), I am puzzled.
 

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Satyr of the Midwest
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What is your baseline timing? Sometimes going too far with it will decrease idle quality. I'd also check the TP voltage at idle.
 

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Satyr of the Midwest
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Well...it can affect both, but I was focusing on quality. Speed is a function of quality. :toothless

For a fixed idle air flow (or IAC duty cycle), advancing ignition timing will raise the speed because a) there is near-zero load on the engine, and b) the peak combustion pressure is higher. UP TO A POINT. When cylinder pressure becomes too high, it's working against the effort to create torque by pushing back the other way (before TDC). This is sometimes why bumping ignition timing can cause a loss in low-end torque (even though it may not FEEL like it).

The idle speed should always be regulated by the PCM, but whether it CAN is the issue, i.e. the PCM may 'learn' that a low idle causes stalling on the particular engine it's controlling, or it may be plenty comfy with its programmed idle that it's always trying to attain (it's a 'target' parameter in the program), or worst of all, it CANNOT control idle speed no matter what it does.

Many times, a fault in the IAC is to blame when the idle surges or it is too low. But like I've mentioned, fault(s) in other systems will be detrimental to idle quality (and speed as a consequence).
 
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