2.0 missing/stuttering upon acceleration

[bushwacker24340]

I have a high mileage Scion that misses/stutters upon acceleration only......(plugs, dist. cap, distributor,& rotor have been changed in the last year), with plugs changed again 2,500 miles ago. After it clears up, it runs great.  I have noticed that if I gradually mash down on the gas thru the gears it doesn't act up as bad as if I really mash the gas thru  each gear.... when I pull out in 1st gear and accelerate hard the engine stutters/stumbles and then clears itsself out and i shift to the  next gear and the same process happens again......after the engine quits stuttering/missing/stumbling the engine winds up perfectly in each gear and will run 100mph if u want it too...... have run some fuel injector cleaner thru it and some carbon cleaner and the carbon cleaner seemed to make the most difference........is there an EGR valve on these engines that could be causing the problem?   ANY ideas or suggestions would greatly be appreciated.

[acad21]

Hi,

I thought about the stuttering.  Have you checked the throttle position sensor?  If it is out of spec it could give the engine management system (computer) the wrong information and cause the wrong air/fuel misture.  Another problem could be the oxygen sensor.  Again, if not working properly it will send the computer the wrong information.  Check around the engine for any vaccum leaks.  One way to do this is to have the engine running, put a small bit of oil on your finger and run it along the vacuum lines.  If you have a leak you will hear a real difference in the engine right away.  Take a look at the fuel vapor recovery system.  If it is plugged, the gas tank will have a vacuum in it that the fuel pump has to overcome to get fuel to the engine.  Lastly, I don't know if this engine has an EGR.  A service manual will tell you and, if so, how to check it.

Take Care,
Ed

[acad21]

Hi,

I have been thinking about your problem since my earlier response.  Here's another thing to try.  Sometimes, the throttle body will get so much carbon in it, it will cause the throttle butterfly to not open and close properly.  Clean out the throttle body with a good carburetor cleaner and then check to see if the butterly shaft is loose as this can also cause weird things to happen.  If it is loose, replace the throttle body.

Take care,
Ed