I am going to find the problem with my Z if it is the last thing I do! I can't walk away from something that is not working right. I won't let it beat me. So with that said as soon as I get time away from work I am pulling the AFM and will try Blues' calibration procedure. I know it's in the AFM. I also know this AFM was not for the 77 280 rather a 76. It has the anti backfire valve in the flap. Maybe that's why it never ran "perfect". Stay tuned for results.

Good for you! You'll eventually prevail.

The anti-backfire valve is in '76 and forward, as far as I'm aware. I had a '75 as a college kid and envied the '76 design, because occasional backfires would bend my AFM's vane.

I came in on the thread rather late and don't have time to re-read the whole thing. However, in my experience on my '78, I have some unpredictability in idle from an AAR that really needs replacement. (I've nursed it along, but it seems to be more trouble than it's worth.) I find my idle gets somewhat irratic if my fuel/air mixture is a bit too lean. I suspect that's because it's easier for an engine to run with too rich than too lean a mixture, and small changes in RPM around idle could cause variations in mixture (e.g. if there's any hysteresis in AFM movement). If the mixture is just a tiny bit rich, the mixture variations are relatively less consequential. Just speculation.

Just a quick run down for you Fastwomen, I started this thread because I was having an issue with the fuel pump running in the "on" position-engine not running. So found that problem corrected it and went into trouble shooting the issue with cold start not working. With help from this forum we found all sensors working properly and fuel pressure being correct. My Z would start after sitting over night but would have an unstable idle at around 900-1000 rpms. Long story short, when I rotated AFM counter weight CW the idle increased to 1300 rpms and she idled smoothly (AAR working). That told me I was running rich during cold start (AFM related). Now we are trying to fix the problem. Thank you for your continued support. How goes the move? I hate moving. Did it too many times in my life.

Yeah, this kind of stuff can be annoying. You can end up chasing your tail.

Can you put the AFM back to where it was when it left the factory? Just as a "documentable" starting point? Is there any goop left on the original lock-down location for you to tell where it originally was? I guess it might not matter if the AFM isn't the one that came with the car though...

Fastwoman, You're saying that the anti-backfire valve was there from 76-78? The only year that did NOT have it was 75?

Yeah Capt Obvious, you got that right! I'm chasing my tail. I can put the AFM back to factory setting I believe. There is no "goop" but I did mark the original starting point. At least I hope it is the original point. I will actually have some time to spend on it tomorrow. I am going to attempt another adjustment before removing it from the car.

I heard that the anti back fire valve only came on the 76 model. Couldn't understand why if it was such a good thing so I will assume I was misinformed. Hope to have good results to post tomorrow.

A back fire in the intake will slam the flap shut and could damage it.

An escape path for the gases is through the AFM bypass passage for setting idle a/f mix.I guess that was not enough so the bypass valve is needed.

It only comes into play when the plugs are wired wrong and fuel is ignited in the cylinder/runner when the intake valve is open.

Sorry to read the AFM adjustment did not do it. It seemed promising. An intermittent bcdd problem or a wiring problem could be the issue.

My '78 has the backfire valve, and the '77, being similar to the '78 in so many ways, would probably have it too. (Blue would be a better authority on this.) I know the '76 has it and that the '75 does not. I picked up a spare AFM that was apparently for a 1980 ZX, and if I recall correctly (because it's in a box in the attic), it was cheapened to omit the valve. Perhaps the ZX'es had some other backfire relief provisions.

Blue, a backfire from lean running is enough to damage the '75 vane too. I remember fixing mine as a college kid by tapping it out with a claw hammer.

RCB, I would check out two additional things on your AFM. First, make certain there is no friction in the vane. You can do that during your beer-can calibration. When you have the beer can w/water hanging from the vane, gently lift the can with your finger, and slowly release pressure. Note where the vane settles. Then gently depress the can with your finger and slowly release pressure. The vane should settle in approximately the same place. In reality, you might have SOME friction, but I would guess if the stickiness only accounts for 1/8" in variance or less, you're probably OK. BTW, WD40 is good for working out old oil in the bearing.

Then find a *mechanical* multimeter (i.e. with a needle movement). Attach one lead to the wiper contact, and one lead to either end of the potentiometer trace. With the meter measuring resistance (ohms), *slowly* move the vane back and forth, and look for smooth needle movement. There should be no sudden jumps that would indicate a poor wiper contact or dirty trace. You can use WD40 to clean the trace. Gently mop up any excess with a paper towel.

1/77 build has backfire relief.

Cool, thanks for the valuable info everyone. At least I know for sure I have the right AFM or at least close enough. Oil.....I recall seeing some oily residue in the AFM where it mates with the throttle body boot. Thanks for reminding me. Will check this out next. Post results later

Hey everybody, I decided to look everything over before tearing into things. I noticed my idle was off... just slightly lower. I started to turn the idle set screw CCW to raise the idle and decided to take it further....curious how high it would idle. I could only get it to 1600 rpms (with set screw). Shouldn't I have been able to get it to idle higher with the set screw?

Will be running tests all day (unless I find something quick) Sat. And will calibrate AFM to eliminated the possibility of it being faulty. Will post results then.

Good luck with the testing!