idle revs and engine toming

[michaeltburke]

Hello there,
Mine is a 1.6 Eunos year 1991. I decided to try to alter the timing to 14 BDTC as opposed to its existing setting of 10 degrees. I also introduced a free flow intake filter system to replace the existing standard one. Typical of many owners I would suspect. I followed internet instructions and connected the GND and TEN on the diagnostics cube . I noticed the revs jump a bit when I did this . I brought them back to 850 with the idle screw and made the adjustments to the timing. Then I removed the jump wire from the cube . However the rev needle will not now return to 850 revs without a 5 second delay. When I reinsert the jumper wire to the diagnostic cube everything works fine again . I now have left the wire in permanently in the diagnostics cube because the pause in returning to idle is driving me nuts . Any advice .... ?

[MX5Spares]

Engine should not be running when doing diagnostic check. Just ignition on position

[michaeltburke]

Thanks for reply. However, and correct me if I am wrong, but to set timing with a strobe light the engine must be turning and GND and 10 connected. When this is achieved is the jumper connection then not disengaged?

[MX5Spares]

Set the timing while engine is running obviously but jumping the terminals then re sets new changes ???

[michaeltburke]

Now Im totally confused. It seems to run fine with the terminals permanently jumped ....maybe I should leave it that way. Chinese cars!

[Steve]

did you happen to fiddle with the ISC while doing the idle?
Troubleshooting guide is here : http://www.miata.net/garage/isc.html

[michaeltburke]

No Steve, I did not touch the ISC , just kept the process simple following a proceedure outlined on quite a few web sites.The jumped idle revs can be set at 850. When the jumper is removed they always drop to 500 or so . I cannot close that gap as there is always about 300 revs between jumped and non jumped. If I adjust the unjumped revs to 850 they become slow to return there when the engine returns to idle from high revs. If left jumped things seem fine. By jumped I mean connecting 10 and GND.