1990 MX-6 rough Idle and Check engine light

[mr300z87]

I am new to Mazdas and have recently purchased a 1 owner 47000 mile 1990 MX-6. The car runs and drives fine and the Auto trans shifts good. The problem I am having is an intermittent rough Idle while in gear. While Idling in gear it will drop down to 400 RPM then bounce between 400 and 600. It will then settle in at around 600. until it decides to bounce around again. In neutral the idle is a steady 750-800 rpm. Yesterday after sitting in some terrible traffic the check engine light came on. Once I started cruising along the light went out after a few minuets. I am very familiar with CEL (MIL) on new OBD2 cars but this one has me stumped and the service manual is all but useless. Any insight is greatly appreciated.

Mike

 

[BOOSTR]

I know my 90 Probe GT had a Self Test connector and by sticking a wire in it and grounding it you could count the number of times the CEL flashed and then look up the code on the trouble code chart. The 4 cyl and V6 have different procedures. I don't know if the Mazda built Probe's used different ECUs but I would tend to doubt it. So which engine do you have?

 

[berserker]

There is a red or green pin connector located on drivers side behind strut tower. get a piece of wire and strip it at both ends. Use wire to insert into green connector and put other end to a ground. Turn ignition over 1 click and the CEL will flash your codes. Here is a link for the codes and procedure too. http://www.mx6.com/forums/1g-faq-engine/115343-faq-how-check-codes-code-numbers.html