My 89 305 TBI idles @550 rpm. Is this normal for this engine or is it too low? Is there a way to increase this. My car seems to idle a little rough when at lights. If I put it in neutral it goes up to 750 rpm.

 

Probably about time to clean the IAC passageways in the TB, and then reset the min idle speed. yes there is an adjustment, but it's hidden behind a tamper proof plug.
A sharp awl can remove the plug, looks like a 3/8" freeze plug, by the linkage.

 

There's a procedure for setting the minimum idle, I highly recommend getting a Chilton's manual, but here's the procedure in a nutshell (first clean the IAC passages by spraying sensor-friendly carb cleaner down the IAC passage while the engine is running).

1. Remove that little plug mentioned above. A sharp screwdriver works.

2. Get a torx bit, I think a T25 but I'm not positive. That's what you'll use to adjust the idle screw (revealed once you remove the cap covering it).

3. Put the car in diagnostic mode (ground the pins in the ALDL connector, there's a document on how do to this in the tech section, you do it if you want to read codes too).

4. Turn the key to ON but don't start the engine. The IAC valve will close, give it about 30 seconds to make sure it's closed all the way.

5. Disconnect the IAC valve.

6. Take the car out of diagnostic mode and start the engine (may have to push the gas pedal down while starting. If it'll start, then dies as soon as you let your foot off the pedal, go turn the idle screw a few times to hold the throttle open farther).

7. Adjust the idle screw until the engine is idling at 450-500 RPM. This is the MINIMUM idle, the computer will keep the idle speed higher than this during normal operation.

8. Turn the car off, reconnect the IAC, go drive around for a bit so the computer can reset the IAC (drive at 30-40 mph for like 5 minutes).

9. See how it idles. If it's still idling too low, start checking other stuff (tuneup time maybe).

The computer regulates the idle speed based on a number of things, particularly temperature. But normal idle after the engine has warmed up is 600-700 for most people. It will probably idle a bit lower in Drive than in Neutral/Park.

 

Thanks, I removed the cap to reveal the screw. I will try the method you provided as soon as I get it running. I tore down the TBI unit and performed the "ultimate TBI" mods., including the regulator mod. I also used a rebuild kit with all the necessary gaskets. Included in this kit was a replacement regulator diaphragm which I replaced. I had a hard time getting the rubber material to stay aligned over the screw holes. I know realize I should have reduced the spring pressure by backing off the reg. screw. Unfortunately, I didn't think of this at the time. So anyway, I don't think the gasket is seated correctly as evidenced by the fact that when I turned the key to the run posistion I saw a fuel spray out the side of the TBI. So anyway I have to rip it apart again and try again. Just happy nothing caught on fire. Thanks for your detailed ins. though.

[This message has been edited by simon (edited November 27, 2000).]