AboutMp2 Expertise I prefer to answer questions relating to the Miata since this has been my area of specific
expertise since 1991. I can answer questions relating to the other Mazda models however
some limitation of expertise may reduce my accuracy.
Experience Mazda technician since 1987, shop owner and specialty are regarding the Miata since 1991 covering mechanical, electrical, trim and body. Specializing specifically in drivability concerns.GKHS 1985, BVC 1987, MNA 1989, ASE Master Technician Mechanical 1995, ASE Master Body/Paint/Collision 1996
Education/Credentials GKHS 1985, BVC 1987, MNA 1989, ASE Master Technician Mechanical 1995, ASE Master Body/Paint/Collision 1996
Question My 1990 miata until recently would run fine but would not idle. I finally got the
car to stay idling but idles very rough and has a miss to it. Also when I rev
up the engine and let it come back to idle, the engine will stop at about 1500
rpm stay there for about 30 to 45 sec (maybe a minute) then drop to about
800 rpm and idle very rough. Could this be a possible coil pack going bad or
something else?
Answer The symptoms you describe could be as simple as ignition break down (ie; a bad wire(s) or a spark plug(s)) It could also be a stuck or non functioning air valve or gum/varnish build up in the throttle body. Mis-adjustment of base timing and idle could also be to blame.
Start simple. As most issues with early Miatas are simple and revolve around common preventative maintenance items.
Check for fire on 1&4 and then 2&3 use a positive grounding test plug since a CDI system like the Miata needs to find a good ground to avoid primary winding overload. A lack of fire on any pair indicates a coil or a crank angle sensor signal, lack of fire on a single lead is a primary wire issue.
If you haven't in awhile get a new set of NGK wires and spark plugs as a first step. See if that resolves your issue, 90% of the time it does. Then move to clean the throttle body, ICS (idle control solenoid) and the PCV while your at it.
The next logical step would be to check the air valve for movement over it's temperature range. If you have let the coolant go and corrosion is present in the system this could be a good indicator that the air valve (a thermostatic device) similar to a thermostat in operation could be stuck or non-operable. It is a cold start device that adjusts bypass air during warm up (a choke of sorts). This is a worst case item so try the basic preventative items first.
service@miatashop.com
"if your good at what you do you should get well paid"
