Rough Idle Question

I've got a '90 with 102K and have developed a really rough idle. Not much of a wrench-turner, but looking for advice as to what may cause this. Sometimes stalls coming to a stop and sounds like it's missing in 1st on acceleration. Up at speed seems to run fine, but do notice a lack of power as I go through the gears.

Air filter on 6/22/04 and wires last year.

So you ran injector cleaner through and checked the blue sparks produced by the spark plugs.

Maybe someone else has something else specific to suggest. I can only look at the Enthusiast Manual:

Disconnect ISC wiring connector while idling and check that clicking is heard from valve. Disconnect oxygen sensor wiring. If fault improves, check sensor. Stuck air flow meter. Check ignition timing. Put a screwdriver against each injector and listen for operating clicks. Check fuel pressure. Defect ECU. Low engine compression due to wear or damage. Air leaks or obstructions in intake system. etc.

Also check the crankshaft nose problem on miata.net

Leon

There is an unused vacuum fitting to the rear of the intake manifold that should be plugged with a rubber cap. If this cap either falls off or gets cracked, air leaks in and causes the mixture to go lean. Look for the clamp that holds a wire harness and has some ground leads under the securing nut. The fitting is right below this clamp.

Best,

Ken