93 Toyota PU overheating/erratic idle


Old 09-17-05, 10:29 AM
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93 Toyota PU overheating/erratic idle

I recently had my mechanic replace the radiator on my 93 toy p/u 4x4 4cyl and check out the engine for the cause of an erratic idle (which happened sporadically at semi-cold engine temps - rapid high to low idle). Before, I had to add coolant frequently and noticed filling and draining from the coolant reservoir after high-speed driving (no overheating). Mechanic replaced the radiator and cleaned the fuel injectors. One day later, while driving at high speeds on the highway, my temperature gauge esclated to near overheating. Also, the idle became erratic, even when the engine is warmed up. I checked the Haynes repair manual and noticed that the thermostat might be a cause of the overheating, but I could not find a related explanation for the erratic idle.

Does anybody have any suggestions on what to check/repair for the overheating and erratic idle? Are the two related?
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Old 09-17-05, 10:47 AM
Join Date: Jun 2002
Location: Long Island, NY
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Yes they are related, air (where coolant should be) getting into air bypass valve causing idle to go up and down.

Yes thermo should be replaced and make sure rad cap is good and holding the correct pressure, either test it or buy a new one.
Old 09-19-05, 05:56 PM
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Thanks for getting back to me. I replaced the thermostat and the PCV valve (which had never been replaced in 168,000mi). The original PCV valve seemed good, however. I think the overheating problem was corrected by replacing the thermostat. I haven't had a chance to drive it enough to be conclusive as I am still having a idle/engine performance problem. Here it is:

When the truck is left in neutral and idling on its own in a parked position, idle is fine. When I give it a little gas, the idle sporadically drops down then comes back to full idle, almost like the engine bogs itself down. It seems to happen a little more frequently when the clutch is disengaged. I quickly checked for vaccuum leaks using a piece of tubing and didn't detect any. Is there anything else I can check?

Thanks in advance!

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