idle adjustment
 

So I am having issues figuring out how to adjust my idle. I have searched around the forums and other places on the web and haven't really found any answers. My adjustment on top of the throttle body does nothing. My car is an '88 na with an emissions delete. It idles at about 450-500, which I think is just too low, since it doesn't always stay running. And it does not idle when cold at all. If I let it below about 1k when cold, it will die. Any help greatly appreciated, if I didn't include enough specifics on my car I am sorry just ask and I will fill you in!

I'm not the best at explaining things, but ill do my best to help you if no one else is offering advice.

Have you checked your timing? Is your bac removed?

Have you tried adjusting the throttle cable? That could solve your problem.

Aside from that there is a screw to adjust the fuel mixture at idle in front of the passenger side strut bar that can help your idle.

Also, the biggest way to adjust the the throttle at idle is for it to be set at a more open position when its let off (in idle position) it's been a while since I've messed with that, I'd have to go take a picture of my throttle body and mark the picture where the bolt is that you can make the adjustment on.

The last part I told you about that opens the throttle more can drastically bring up your idle as it basically sets where the throttle stops when you let off the gas which is preset by Mazda, and the bolt is sealed in place iirc though the seal can easily be broken.

The ecu is set up for the car to idle at 750 iirc, so even if you bring it higher the ecu will fight to bring it back down.

My bac is removed, and I have not checked my timing. I'm not sure how to do that. I have adjusted my throttle cable but that is such an inaccurate way to raise the idle. It made my idle jump from 600-1500 day to day. I swapped coils and wires with a friend and put new plugs in, no luck. I did a compression test, 95 on front 90 on rear, three even pulses on both rotors. I checked for vacuum leaks, pretty sure I don't have any. I wonder if it could be leaky/bad injector(s)? Any help is appreciated thank you!

You need the BAC.

If the adjustment screw on top of the TB has no effect, then you've go some other problem(s) that you need to fix before you can start worrying about idle. Check for vacuum leaks first and fix them. Then check BAC and TPS for proper function. Adjust the TPS. 1V at idle, 5V at WOT with a warmed up engine. TPS problems can really play hell with proper idle.

1. NEVER use the throttle cable to bring up the idle. Leave some slack on the cable.

2. Put your BAC valve back on. You dont need to hook up the coolant lines that connect to it.

3. Make sure you set the TPS to 1 volt after the car has been fully warmed up.

4. Use starting fluid to spray around the intake area(not into the intake!) if it revs up or smooths out then your leak is in that affected area.

5. If you play with your timing then make sure the car is idling below 1100? rpm. Above 1100? the timing is advanced, you will wont be able to get the timing marks correct.

I just realized my last post on this thread was pertaining to my weird rough idle/misfire situation. But about the idle adjustment, my screw on the throttle body doesn't do anything so I will be checking for leaks with starting fluid. I recently adjusted my tps to 1V at idle and 5V at WOT. And I would like to check my timing but don't know how to, all I know is that its on the CAS.

The search feature will bring up countless threads on how to check the timing.

Very simple.

Put the BAC back on.

Adjust throttle cable as per instructions in FSM/Haynes. There should be a slight bit of slack in the cable when the throttle is closed.

Adjust idle as per instructions in Haynes/FSM. Junp initial set coupler, perform idle adjustment.

Adjust timing as per instructions in Haynes/FSM. Jump initial set coupler, adjust CAS using a timing light.

Readjust idle again.

Without the BAC the car will never idle correctly.