wandering idle
- Thread starter H/O84
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code 12 is no distributor pulse "The engine will not run with a "hard" code 12 set"
TPS seems to be just about the flimsiest part in the "feedback carburetor" system. They first develop dead spots that confuse the computer for a while, then wear out entirely.
One thing the computer controls that you didn't mention is fuel mixture, by way of a solenoid in the carburetor. For that to work right two "idle mixture" needles must be adjusted by hand, in "closed loop" at idle in Drive, so the computer is "centered" within the range of control it has to work with. You watch how you're doing with those needles with a dwell meter. (Sweep dwell meters aren't easy to find these days. Some digital multimeters have a dwell function, but sweep is easier to read.) The catch-22 is, everything else has to be working right before you even bother checking the needles. They're likely to need backing out to richen the mixture, due to E10 or whatever you have at the pump these days.
EDIT: Oops -- I keep forgetting, there are TWO DIFFERENT VERSIONS of the mixture control system. Both versions have an idle air bleed valve as well as the two needles. If the bleed valve has a letter stamped on its top, then you adjust the needles and leave the bleed valve alone. If the bleed valve has no letter, then you adjust the bleed valve and leave the needles alone. Either way, you use the dwell meter. It's an arcane system and you really need the factory shop manual, which can be dense and confusing.
One thing the computer controls that you didn't mention is fuel mixture, by way of a solenoid in the carburetor. For that to work right two "idle mixture" needles must be adjusted by hand, in "closed loop" at idle in Drive, so the computer is "centered" within the range of control it has to work with. You watch how you're doing with those needles with a dwell meter. (Sweep dwell meters aren't easy to find these days. Some digital multimeters have a dwell function, but sweep is easier to read.) The catch-22 is, everything else has to be working right before you even bother checking the needles. They're likely to need backing out to richen the mixture, due to E10 or whatever you have at the pump these days.
EDIT: Oops -- I keep forgetting, there are TWO DIFFERENT VERSIONS of the mixture control system. Both versions have an idle air bleed valve as well as the two needles. If the bleed valve has a letter stamped on its top, then you adjust the needles and leave the bleed valve alone. If the bleed valve has no letter, then you adjust the bleed valve and leave the needles alone. Either way, you use the dwell meter. It's an arcane system and you really need the factory shop manual, which can be dense and confusing.
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First use avoltmeter to see what the TPS is putting out and if it has flat spots. It should read 0.5 volts at closed throttle, about 4.5 volts at WOT, and should be getting 5.0 volts in reference voltage from the ECM. Disconnecting a major sensor like the TPS usually sends the ECM into limp mode where the carb defaults to full rich. Have you used a analog dwell meter to see what commands the ECM is sending to the carb? Rich command means it is trying to offset a lean condition. Lean command means it is trying to offset a rich problem. Another issue may be the lockup solenoid in the trans, pretty common for them to fail and cause stalling problems at stops.
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