Idle Speed Adjustment

[courtenay]

Can someone give me some advice on the best way to adjust both the throttle stop and idle screw to achieve the optimal idle speed? My car has been idling around 1200RPM. I adjusted the throttle stop to bring it down to 800 - 900 RPM, but now, when I decelerate to, say, go around a corner, and then get back into the gas, the car bucks and hesitates. Also, when I restart it when hot, it has a lot of trouble idling and will stall. My car is an 80 Fuel Injected.

[4uall]

this might help

http://forum.fiatspider.com/f08/viewtop ... 27#p144327

[courtenay]

Thanks, Jay, but it doesn't quite do it. I have made the adjustments when the car is warm. What I'm wondering is what the adjustment relationship is between the throttle stop and the idle speed screw. In other words, for example, should I adjust the throttle stop to 1100 RPM then drop the revs with the idle screw? I'm really at a loss here.

[rlux4]

What works for me is having the throttle stop set so that there's a very slight slack in the cable, and then adjust the idle screw (air bypass) to get my idle around 850 rpms. This is with the engine at operation temp. On my car that's seated and then backed out about 3/4 turn. To get it working correctly though you have to be sure and have no air leaks: vacuum booster, vacuum to the fuel pressure regulator, vacuum advance lines and the boot and it's fittings. If you can't get it to idle down where it should you may be getting false readings from the AFM resistor or ignition timing may be off. I learned what I know about it from Brad Argigue's manual in the FI section, it's here if you don't have it yet:
http://www.artigue.com/fiat

Ron

[bradartigue]

Can someone give me some advice on the best way to adjust both the throttle stop and idle screw to achieve the optimal idle speed? My car has been idling around 1200RPM. I adjusted the throttle stop to bring it down to 800 - 900 RPM, but now, when I decelerate to, say, go around a corner, and then get back into the gas, the car bucks and hesitates. Also, when I restart it when hot, it has a lot of trouble idling and will stall. My car is an 80 Fuel Injected.

Step Zero: Test your brake booster connection. Unplug the brake booster hose at the manifold and block it off with a cap. Drive the car. Did the problem go away? Keep in mind the brakes will be a little harder to press but if the car runs perfectly or very differently (high/low idle, etc) with it unhooked then it leaks; fix it.

If that isn't it then remove the air bypass screw and clean the orifice and the screw. Replace the o-ring. Fully seat the idle air bypass screw. Slacken the throttle cable nuts so there is no tension on the throttle. Start the car and warm to normal (two fan cycles). Set the stop screw to 800 RPM. Set the air bypass screw to bring the idle to 850 RPM.

Drive it. Is the problem resolved? Yes, great, no, read on:

Test the throttle position switch (I can't recall the values, go to http://www.artigue.com/fiat and download the book I wrote on it, or look in your shop manual). If off then set correctly.

Drive it. Is the problem resolved? Yes, great, no, read on:

Stop the car and manually advance the motor to line up the crank at TDC and the cams at the alignment holes. Does it line up perfectly? No? Reset timing belt. Yes? Attach timing light and start motor. Set timing to 10 degrees behind top dead center with the diaphragm vacuum line pinched.

Drive it. Is the problem resolved? Yes, great, no, read on:

Stop the motor. Check that the distributor vacuum advance works by drawing vacuum. Does it hold? If you don't have a handpump then blow into the line (don't suck - if the diaphragm is bad you'll suck in dirt!). Solid? If not then replace. If so then read the plugs. Brown to brownish white = normal; black = rich; white = lean. Which is it?

Brown to brownish white? Yes, great, no, read on:

Test the AAR operation (see my book). Using propane (not fire, just a light amount of propane from a small tank) around the air hoses try and find a leak. If the engine speed goes up when you place propane near the hose then you've found one.

[courtenay]

Wow - thanks, Brad. That should about cover it!!