I recently finished rebuilding the motor on my 1992 Miata and started it this Saturday. However it will start and then immediately die. But when I disconnect the connector to the IAC Valve it allows the engine to idle albeit very rough. But in order to get the car to idle even close to the 850 rpm that's recommended, the timing has to be set way before BTDC like the mark is perpendicular to the ground and the idle adjust screw doesn't seem to be really doing much of anything to help it. And the car still idles very rough. But when you give it gas it seems to do fine above 2000 rpm.

FYI I did jump the TEN and GND on the Diagnostic and when I installed the timing belt I double checked that all marks were lined up, and I have double checked that my spark plug wires are going to correct coil pack.

I haven't yet checked for any vacuum leaks with carb cleaner but on visual inspection I haven't found anything to suspect of a leak. Does the IAC Valve need to be replaced or is the fact that it will idle without it plugged in mean that the TPS is not properly adjusted or telling the ECU that it is closed?

Thanks,

Micah

 

Set #1 to TDC power stroke (like you are setting the timing), remove the valve cover, and take these photos:

-one top down shot clearly showing the #1 cylinder cam lobes
-one front shot clearly showing both cam marks with enough resolution to clearly count teeth on the belt between the cam marks
-one shot at the crank gear clearly showing the notch lined up with the arrow in the oil pan (you may need to remove the harmonic damper to get this photo)

 

Here are the pictures. So far as I have seen and read everything looks good.

 

what are your compression numbers?

are you still using the factory ecu?

 

Cylinder #1: 135
Cylinder #2: 135
Cylinder #3: 140
Cylinder #4: 137

From what I've read those are on the low side but still within the acceptable range for compression and are all within close range of each other. And yes I am still using the factory ECU.

I have had the battery disconnected since Monday while I was taking the engine apart to take the above pictures and was waiting on a reply so I hadn't reconnected it until today before I started to warm up the engine before the compression test. I had disconnected the AFM because I changed out the air filter and I forgot to plug it back in when I started the car, however the car started fine and settled on an idle of about 2000 rpm and it was running smoothly. I was able to set the timing to 10° BTDC with it still running smoothly and it got the idle to go down in rpm. But since the AFM was not connected the Diagnostic was throwing a code 8 and 10, so I reconnected the AFM and it immediately died. Now I am back to square one because the car will start and will continue to run if someone is giving it some throttle but will die fairly instantly with no driver input.

 

Also disconnecting the AFM again to try and repeat the previous "success" does not yield anything better, it simply dies as I believe it should.

 

Figured out my problem. The intake manifold was not tightened down properly thus causing a massive vacuum leak. I tightened it down and now the car idles like it should and runs well.