# 94 Chevy S-10 4.3 vortec pickup idling goes up and down



## desireefrymyer (May 23, 2011)

Hello and thanks in advance for any info. Can't seem to find out why it idles at 1000rpm's and also revs up and down. Checked hoses, replaced a few. New spider injectors put in, cleaned throttle body out, took off plenum cleaned out every where there was carbon built up, cleaned air control valve, checked fuel pressure seems good. also when hooked up to fuel pressure gauge it goes up and down also as it misses. Help!!!


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## octaneman (May 13, 2009)

Hi desireefrymyer



Extract any trouble codes and please post them. Fuel pressure oscillation is caused by either a bad fuel pump or a fuel pressure regulator. With engine off disconnect the fuel line and hook it directly to a fuel pressure gage. Turn the ignition and wait until the line pressurizes, look at the pressure and see if its steady and compare it to your specs. If the gage pressure drops the pump is gone.


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## desireefrymyer (May 23, 2011)

No codes when we checked before we disconnected things. Now there will be codes because of that. When you say disconnect the fuel line and hook it directly, help me out, fuel line where? I think that whatever is making the idling rev up and down is making the pressure gage go up and down since it is in sinc with the idling. Could this be the idle control valve? Did clean this also.


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## octaneman (May 13, 2009)

The IAC does not control fuel delivery to the injectors, what happening is the engine is being starved for fuel. It will be a good idea to double check your IAC motor by using a 9v battery, to do this connect the +ve and -ve to the IAC voltage pins and see if the plunger moves. Reverse the polarity and see if it retracts. The movement of the plunger has to be smooth both in and out, if there is a dead spot on the IAC you will notice instantly. 

I believe your engine uses a throttle body type injection system, there are 2 lines on the throttle body. As you are looking at the front of the engine, one line is bigger and threads straight in ( main pressure) and the other is at an angle (return line) hook the gage on the main line and post its maximum pressure output. You will need a T fitting to hook up your pressure gage to do the test.


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## desireefrymyer (May 23, 2011)

Sorry I should have told you that ours is a CPI injection system


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## octaneman (May 13, 2009)

Locate the fuel rail to where the injectors are and look for a schrader valve, it has a cap on it like an ordinary tire valve. You hook up the gage there, but be extremely careful because the line is pressurized. You will need to depressurize the system by disconnecting the fuel pump fuse and run the engine until it dies. Hook up the pressure gage and compare it to your engine specs.


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## desireefrymyer (May 23, 2011)

hey thanks alot we will try this tomorrow and will let you know


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## whatup (May 22, 2011)

ck the egr valve if it has carbon built up on it that will cause your prob


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## desireefrymyer (May 23, 2011)

EGR valve was cleaned. Took plenum off cleaned everything, there was carbon built up. Put back together no difference


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