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Dear James, Recently at my shop we changed the cylinder head on a 22 RE, 1994 Toyota Pickup. When it is cold it runs fast like it supposed to. When it gets warmed up, it really runs rough at idle and the idle speed goes up and down. I have checked for vacuum leaks with carb cleaner and none exists. Any advice would be appreciated to solve this troublesome problem. Old Joe in Panama City.

Old Joe, In 1994 the 22RE was loaded with vacuum hoses and thermo vacuum switches. I suspect that your problem is due to a thermo vacuum switch. You say it runs well when cold, yet runs poorly when at operating temperature. On the early model Toyota's they have a diagnostic plug on the fender for you to troubleshoot certain sensors. When you open the cover to the diagnostic cover you will see a label to tell you what sensors you can monitor. Look for the "O2 1" label and set your DVOM to your lowest DC voltage scale. With the engine cold and running, see what the voltage reads on your meter. It should be around .2mv to .9mv and bouncing up and down, as it is sending commands to the computer. When it starts to run bad, look at the O2 readings again, see if they are stuck around .2mv. If so, then the engine is running lean like you suspect. The only thing I know on this engine that will make it run lean is the EGR valve getting vacuum, when it shouldn't! Or the easiest way to prove if this is the problem, pull the vacuum hose off the EGR valve and see what happens. Hope this helps you out....

 

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