Hello everyone, maybe somebody can help me? My 1977 280z is running rich at idle and the idle mixture on the AFM doesn't seem to help.

I spend the last few days cleaning the electrical connections and timing the ignition again as it was out of spec. The car runs way better but the AFR gauge I temporarily installed still shows 11,5 at idle. I'd like to bring that down (or up depending how you look at it) to 14,7 as the car stinks of gasoline. The previous owner mentioned that the car running rich was the reason it didn't pass inspection (auction company didn't mention it had no valid inspection on it, APK over here in the Netherlands).

After cleaning all the connections and checking the timing I tried messing with the idle air mixture screw but that didn't help. When turning clockwise a bunch the car did start to run richer at some point but when turning anti clockwise it didn't get past 11,5 AFR.

Can anybody help me diagnose the problem? I would really like to drive the car on the road before the winter stop (oldtimer insurance). Also still waiting on some parts from Zservices EU but some are on backorder.

In my quest to make the car run as it should I did notice the ignition coil is a 1,5 ohm unit with a total resistance of 2 ohm with the external resistor. I believe it needs to be closer to 1 ohm total so I'll probably replace the coil with a 0,5 Ohm one. Can somebody confirm this?

Edited after coffee kicked in...strikethrough does not show in the snippet.

The idle air screw only adjusts idle RPM, not the fuel-air ratio. It's difficult to lean out the mixture on the EFI engines. Hope that you find something wrong somewhere. Edit - sorry, just looked at your picture and see that you meant the AFM screw.

One possible reason for a rich mixture is a leaking fuel pressure regulator. The diaphragm can crack and let fuel directly in to the intake manifold through the vacuum reference hose.

Another possibility is a lack of the vacuum on the FPR vacuum port. A disconnected or cracked hose or a connection to the wrong vacuum port. The FPR reduces fuel pressure in proportion to intake vacuum. Check the hose for fuel to see if the FPR is leaking, and make sure it's connected directly to an intake vacuum source.

Sticking injectors is a possibilty.

A maladjusted AFM is a possibilty. Generally, the AFM spring should not be messed with. But sometimes it's too tempting. See if the glue blob on the adjustment wheel is intact.

I had also found that my aftermarket AFM was set to run rich. I had to use an old original AFM to pass emissions inspection in Oregon.

Edited 18 hours ago18 hr by Zed Head

I have already ordered some new vacuum lines just in case as some of them seem a bit hard and if one cracks it can cause a lot of problems. But as far as I’ve seen my vacuum should be fine. My AFM unit did seem pretty dirty on the inside so I was thinking of cleaning it in a ultrasonic cleaner with an electronics friendly cleaner. Also somebody did have the AFM open at some point in time but I don’t know if they messed with the gears inside.

I do have a pretty good understanding of the 280z EFI system and the inner workings of the components so I’m not afraid to touch the AFM unit but I would still like to ask for some tips and directions to look at.

All in all the entire engine needed a tune up as many contacts where slightly corroded or out of spec and I suspect the car was "tuned" at some point as it has an aftermarket O2 and crank angle sensor, neither one hooked up to anything. The car runs way better now but it’s still running too rich. My vacuum lines should come in this week and I’ll do some more component testing and cleaning before I start messing with the AFM itself.

Edited 5 hours ago5 hr by Mitchel0407
adding some details

Your car should not have a crank angle senser, that is for a turbo car. Your car is also pre 1980 when factory O2 sensers were just coming into play. Someone may have installed the O2 senser to try to adjust the AF ratio, but it is not factory.

Have you checked to see if your Throttle Position Switch is adjusted correctly to let the ECU know the engine is at idle?

What does the AF ratio do when you drive the car?