1978 Mazda Cosmo Automatic TransFACTORY OEM SERVICE PROCEDURE

1976 Models

  1. Turn ignition on. Unplug connector at both solenoids. A "clicking" sound should be heard from both solenoids when disconnected. If not, replace solenoid(s).
  2. Connect tachometer to engine. Start and run engine at idle. Disconnect air hose from deceleration control valve at air cleaner. Block air hose opening with hand. See Fig 1. Engine speed should not change noticeably.
  3. With hose still disconnected, disconnect coasting valve solenoid. Vacuum should be felt at end of hose. With anti-afterburn solenoid disconnected, vacuum should be felt at end of hose.
  4. Reconnect both solenoids. Disconnect coasting valve-to-intake manifold hose at deceleration control valve. Plug end of hose and open end of air outlet hose. Increase engine speed to 4000 RPM, then quickly release accelerator. Vacuum should be felt at air hose opening. If not, replace deceleration control valve.
  5. On manual transmission equipped vehicles, disconnect idle switch and coasting valve solenoid lead to battery. Connect a voltmeter to lead from control unit. Start engine and slowly increase engine speed to 2000 RPM.
  6. Slowly decrease engine speed and record RPM at which current starts to flow. Current should start to flow at 1050-1250 RPM and continue to flow until idle speed is reached.
  7. Slowly increase engine speed and record RPM at which current stops flowing. Speed should be within 80-220 RPM of current flow RPM. Reconnect idle switch. Increase engine speed to 2000 RPM. Push idle switch lever toward idle position. Current flow should stop.
Fig 1: Deceleration Control Valve Test
G09310009Courtesy of MAZDA MOTORS CORP.
Factory Service Tools

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.

Shop Manual-Ready ToolsCompare Repair QuoteQuote Shield Pro

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

Rather have a pro handle this?

A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.

Comes to youSame-day available12-month warranty
Get a Free Quote

No obligation. See pricing before you book.