QuestionQUESTION: Tried to adjust idle speed. When jumpering terminal 10 to ground terminal in diagnostics block the engine shut down. What would cause this? Is this the proper procedure?
ANSWER: Be sure the AC is off as well as other electrical items. Be sure your in GND & TEN.
You may have to set the idle stop higher than normal to maintain some level. Be sure to set the timing first then idle down then cross check the timing once you establish the appropriate idle.
It's a good practice to clean the throttle plate and the ICS ports since gum/varnish can collect and cause operational issues. All part of fine tuning.
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QUESTION: When the car is first started it idles fine, however after driving it a while it has a rough idle, otherwise while driving runs smooth. Any suggestions as to what my problem might be, solutions?
ANSWER: The symptoms you describe may be related to the air valve (a cold start device, similar to a choke) not closing after warm up. If the air valve remains open the idle air to fuel ratio will be high which can cause idle issues. The air valve is located on the driver's side of the intake manifold on top (looks like a big "D" cell battery) it has two coolant hoses attached to it and is held on by four 8mm head fasteners.
Now a common problem that could also be to blame is ignition breakdown. If you have not changed plugs and wires in say 20-30k then it's always a good baseline place to start. Use NGK plugs BKR5E and NGK wires RC-ZE21 this will ensure the right fit and proper ignition charge reaching the combustion chamber. Ignition breakdown can cause numerous drivability concerns with a Miata. Better to do common preventative procedures before going in for more major surgery.
The air valve is a thermo-mechanical device it uses coolant temperature to operate (similar to a thermostat). Cleaning the intake side is great since gum/varnish (blow by products) can collect and restrict movement. The only way to test the device is to cool it in your fridge (below 32 degrees F) mark it's position, then warm it in hot water or with a hot air gun and monitor the travel of the valve. If it moves it works if it doesn't it's stuck or failed. The replacement is pricey so the test is very much worth while.
service@miatashop.com
"If your good at what you do you should be well paid"
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QUESTION: How much travel should I expect the air valve to move when tested?
AnswerMaybe a centimeter. When it is cold that the assembly is retracted (towards the front - hose barb side) then, can you get a liquid (great time to use a throttle cleaner) to flow from one port to the next port. When cold? When hot? That is how you tell if it can seal air flow or not when installed. If it seals it works if not you may need to replace it.
service@miatashop.com
