My '90 (short nose crank) miata suddenly developed a low stumbling idle (200 to 500 rpms) with intermittant surges to 1,500 rpms and then back to stumbling. It runs smoothly at anything above 1,500 rpms and pulls hard to redline through the gears.
The end of the crankshaft seems to still be firmly attached, the timing is steady and the crankshaft pulley bolt is still tight.
The car has 77,000 miles on it and has been supercharged for the last
50,000 miles. There are no obvious vacumn leaks and the symptom developed over the course of a 60 mile drive. Spark plugs and wires are about
15,000 miles old.
Any ideas?
Roland Smith Wrightwood, Ca