3VZE Idle fluxuation when outside air temp changes
I have a 1988 Toyota Pickup - 3VZE. I have troubleshoot the symptom to the outside air temperature (not engine temp). Engine is at normal running temp with this problem. When the outside air is warm (above ~80°F) the idle will be low. When outside air is cool (below 50°F) idle is high, thus causing the idle fuel cutoff to engage at a stop sign with the brake on. Is the AFM (Air Flow Meter) the only component in the engine compartment that measures air temp? I have measured the AFM with a DVM and it vaguely falls within Haines manual temp chart.
Welcome to the forums! :)
It's possible that yer Engine Coolant Temperature (ECT) sensor may be bad. Have you measured the resistance when cold and when at operating temp? ;)
How good are yer vacuum lines? How many miles do you have on the vehicle? Have you inspected/cleaned the Idle Air Control (IAC) valve? It should be located under the throttle body. I believe the IAC valve is coolant based only. If the coolant lines to the IAC valve is clogged up with debris or build up, it could cause issues with yer idle. ;)
Also, have you inspected the EGR valve fer any issues? ;)
Good question. Yes, I have checked the ECT resistance at both cold and at operating temp. If fact, with the connector unplugged, I jumpered the connector with different size resistors to mimic a hot engine which had not effect on this idle issue.
Most of the smaller dia. vacuum lines have been replaced. I have also checked for leaks using a low flow propane around the various joints and hose connections.
I have removed and cleaned the throttle body. In this old version of the 3VZE, the IAC is incorporated into the throttle body which I cleaned as well. I did suspect this for a while, but that would imply it is related to Engine Temp and it is not. Also can’t find a replacement throttle body.
EGR tested good.
As stated in the original post, idle speed is directly related to the outside air temp:
• Start engine on a warm afternoon at the end of the work day (outside temp at 70°) = idle low.
• Engine at temp, driving down the road on a cold day (outside temp at 40°) = idle high, fuel cutoff with brake on at stop sign.
• Engine at temp, park Pickup for 15min in garage (engine compartment air heats up), drive again (outside temp at 40°) and idle is low for the first couple of minutes, but after that first mile, the idle high & fuel cutoff with brake on (air entering air filter is cold).
As far as I understand the 3vze setup, the VAFM has the only sensor the reads the incoming air temp. How good is yer wiring harness? Has anyone messed with the VAFM before? Does the connector look like it's been pulled apart and repaired? ;)
You might be able to source another VAFM using www.car-part.com and there might be a parts yard near you that might have it. ;)
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