well sort of - after i pullled the intake plenium and fixed the creature damaged vacuum leak, brazed my egr tube, cleaned the intake butterfly with throttle body cleaner, and put it all back together the car ran great except for one thing:

in neutal it was idleing at amost 2,000 rpm. In gear it was idleing ok, dropped right down to 900 rpm.

I checked all over for vacuum leaks with the wd40, and found none. I thought maybe when I cleand the intake butterfly I had pushed some of the goopy carbon into the butterflys way, so it wasnt closing all the way.

I found an interesting little screw next to the throttle cable cam, took a good look at it and sure enough, there is a screw that controls how far the buttterfly closes when the foot is off the gas pedal.

I started the car up, let it get to temp, turned the screw and I could see the plate closing more and more, and the rmps started dropping - got it right down to 900 rpm at idle!

I think maybe the previous owner had messed with it - dont think it should normally have to be adjusted for any reason - but in my case it fixed my high neutral-idle problem.

That's not the idle speed screw. It adjusts the *minimum* idle. It should be adjust to an RPM below the 900 RPM idle the ECM wants.

If you don't have a scanner, crank it in until the idle goes up, then adjust it down until the idle doesn't drop anymore. At the point, the ECM will have control. Then crank it out 1/2 more turn.

Generally, that screw is adjusted to 550 RPM with the IAC all the way in or for 40-60 IAC counts on the scanner.

thanks - the car is running 100% now - everything is perfect!

Cool.

If you set the screw for the exact 900 RPM, the ECM can't control the idle and deceleration cutoff. The ECM needs to have control.

I've fixed many Fiero idle problems by just setting that screw correctly.

I thought GM capped those. The cap missing would be a sign someone fooled with it....

Like Terry said, Generally that screw shouldn't be messed with. And if it's set wrong it will cause problem...

When it is, It's usually by some boob that still hasn't learned how to work on computer controled engines. Those stop screws are basically set and forget. Only time you normally mess with one is when the TB or TBI is replaced.

One thing you may want to do now is reset the ECM even if there are no codes. That will clear any learned data that is no longer valid since the change.

[This message has been edited by theogre (edited 05-27-2001).]

orge the cap is 4cyl only no cap on v6

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Question wonder and be wierd

quote Originally posted by ray b: orge the cap is 4cyl only no cap on v6

There is an idle adjustment screw on my 4cyl? Not as if I would be messing with it, but I have been looking over that throttle body quite well recently for vac leaks.

84-86 or 87-88 ray?

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'87 Coupe 5spd.
AIM:FieroJoe87

Joe,

Both the 4 cyl TBI have adjustments.... And the screws are capped. They should Never be adjusted unless the TBI is replaced.

The old 300 TBI(84-86)requires a special tool be used when setting it. The tool is required to plug the IAC passage. If the IAC isn't completely sealed the setting will be wrong and will cause trouble.

The 700(87&up) has a special procedure but you only need a screw driver. Unlike the 300, the ECM has a way to force the IAC closed on the 700 for base idle adjustment.

When moving a used TBI to another motor it is rare to need base idle adjustment. (Unless the TBI came off a diferant displacment engine... But that's something you usually want to avoid.) Even after rebuilding you usually don't need to adjust them...

Obviously there's no sure way for a new TBI to be preadjusted reliably, so in that case you'll nearly always need to adjust them.

In most cases Idle problems on 4 cyl, especially DIS, are Not caused by the TBI.