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Toyota Repair/engine bucking issue


QUESTION: 1985 Toyota 4Runner 4 cylinder efi  The engine will buck/slight backfire  when the a/c is on.  Turn the a/c off and the bucking goes away,  runs normally.  I have tried it at various speeds and with the a/c fan at various speeds.  I have an aftermarket electric fan installed.  All connections look good. All vacuum hoses are in good shape and attacked.


ANSWER: When the a/c is on there is extra load on the engine which may cause weak ignition parts to fail, I would recommend doing a basic tune up using new plugs, wires ,dist. cap and rotor

---------- FOLLOW-UP ----------

QUESTION: All that you mention has been done within the past 4 months.  I have checked the plugs, they look fine.  I have checked the dizzy cap and rotor,  fine.  The plug wires and coil wire al look fine,  no corrosion.

Two things to to note:  It runs fine at idle with a/c on,  no hesitation or missing. Only starts bucking when in gear and rolling.  Secondly,  when it starts bucking I hit the a/c off button and it stops bucking immediately.

Any other suggestions?

It's possible that the a/c compressor is the problem, it may be starting to seize up or the a/c clutch may be going out, either of these can draw too much current, you may also consider checking the alternator output, most autoparts stores like Autozone will check the charging system for you at no charge.  

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Ted Ritter


I have more than 28 years experience as toyota technician, I will be able to answer most questions related to the Toyota product line up to the present year models,I am located in the US but welcome questions from other regions of the world. When asking a question please provide specific information: year,model, engine,transmission information. Provide as much information as possible including a brief repair history if possible. I have been a volunteer here for more ten years an have answered over 16,000 questions helping Toyota owners with their problems and save thousands of dollars without any compensation, some of my answers are published on many other websites including google and various automotive forums. DONATIONS ARE VERY MUCH APPRECIATED, IF YOU HAVE RECIEVED HELPFUL INFORMATION PLEASE MAKE A DONATION. AS OF TODAY (JULY 22, 2014) ALL REQUESTED GRAPHICS, ILLUSTRATIONS, DIAGRAMS, PHOTOS, WILL REQUIRE THE MINUMUM DONATION UP FRONT.


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