4AGE: 88 N/A engine code Q

[blazer9903]

Hello out there - I'm new here. I've been working on these 2's for years, between my dad and I we have 4 of them; '86 NA Hardtop, '92 NA hardtop, '88 SC and '88 NA - all are MT - -- These are the 4 left of the 10 we've had over the last 8-10 years or so. I was always sorry to loose the gold '86 hard top with no mandatory options (that was the best one I'd ever driven) - While I know a little something, I'm still no expert as my dad always preferred to write a check than do the work; whereas I enjoy doing the work. Anyway, thats my introduction, on to my question.

I'm working on the '88 NA 4age right now, its running great aside from the worn synchro in 2nd. For all intensive purposes, the engine is stock. (has a monza cat-back) Though its running very nice, I'm getting a check engine light - I have reset it and it gives an all clear before startup, but after startup, it immediately codes 12 and 21. I know 12 is the o2 sensor, which I'll replace this weekend, but 21 "no RPM signal within 4 seconds of startup" - thats the one I can't seem to find the cause of. The distributor and coil were replaced before I got my hands on the car, and all the wiring looks good. I'm getting 12v off the distributor harness and variable voltage increasing with the engine speed at the terminals on the coil. The tach is working fine. It doesn't seem to effect the performance at all, but the damn light is just annoying as hell. I'd finally gotten to the point of getting ready to just live with it, but my intention is to restore this car to "new" condition and I see that there are a lot of people on here with more knowledge than me. Any help is appreciated!!