1987 Mazda Truck Idle speed

Tiny
IMNEZRIDER
  • MEMBER
  • 1987 MAZDA TRUCK
  • 4 CYL
  • 2WD
  • MANUAL
  • 98,000 MILES
After warming to normal engine temperature, idle won't "settle down" below 1100-1200 RPM's. Doesn't seem to be alinkage problem. Possibilities?
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Sunday, March 29th, 2009 AT 11:26 AM

8 Replies

Tiny
RASMATAZ
  • MEMBER
High idle could be the caused of vacuum leaks, automatic choke/fast idle cam adjustment, worned throttle shaft, and throttle plate sticking.
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Sunday, March 29th, 2009 AT 11:38 AM
Tiny
IMNEZRIDER
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So am I understanding this is an "old school" carbureted engine with no sensors, etc?

Thanks for your earlier response also.
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Sunday, March 29th, 2009 AT 12:54 PM
Tiny
RASMATAZ
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Check the choke plate if its sticking closed and not fully opening this will cause a fast idle. Have you adjusted the curb idle screw. You have a throttle position sensor on the Carb, an intake air temperature sensor in the airfilter canister and oxygen sensor on the exhaust manifold. Check and test all of them.

Too fast an idle speed. If an engine without computerized idle speed control is idling too fast and refuses to come down to a normal idle speed despite your best efforts to back off the carburetor idle speed screw or air bypass adjustment screw (fuel injection), air is getting past the throttle somewhere. Common leak paths include the carburetor and throttle body gaskets, carburetor insulator spacers, intake manifold gaskets, and of course, any of the engine's vacuum fittings, hoses and accessories. It is even possible that leaky O-rings around the fuel injectors are allowing air to leak past the seals. Another overlooked item can be a worn throttle shaft and a defective idle speed speed control motor/valve stuck in the extended (high idle speed) position/throttle position sensor. Also the throttle plate could be binding in its bore and kinked accelerator cable, coolant temperature sensor might not be operating properly misleading the computer that the engine is still cold and computer throwing fuel at it raising the idle speed.
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Sunday, March 29th, 2009 AT 1:58 PM
Tiny
IMNEZRIDER
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Thank you for the input. I guess what I need to know is. How do I determine whether this engine is "computerized" or "non-computerized"? Again, it's a 1987 Mazda B2000.
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Sunday, March 29th, 2009 AT 5:36 PM
Tiny
RASMATAZ
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The info I've gave is for 2.2/2.6L as for the 2.0 having a computer-Check behind the right kick panel if there's a square box there with a bunch of wires going into it-could be the ECU or the feedback control unit. I believe yours is a feedback carburetor.

Look besides the carb if you can see some sort of a stopper screw that will open and close the throttle plate if so try dropping the idle from there.
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Sunday, March 29th, 2009 AT 6:10 PM
Tiny
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Ok. That helps. I'll start checking tomorrow and go from there and let you know what I'm finding, etc.
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Sunday, March 29th, 2009 AT 7:22 PM
Tiny
RASMATAZ
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The idle speed screw is on the same side of the automatic choke assy.
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Sunday, March 29th, 2009 AT 8:06 PM
Tiny
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Gotcha. Thanks
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Sunday, March 29th, 2009 AT 8:45 PM

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