Engine Performance problem
1994 Ford Probe 4 cyl Two Wheel Drive Automatic 159700 miles
Need some help from some advanced mechanics out there. Got an EEC-IV controlled 94 Probe, automatic. It starts up and idles cold at 2000rpm, then slowly (~3min) drops to normal - 750 or so. The trouble is, when I am idling and if I tap on the gas and let go, it will go back up to that 2000 and stick there for a few seconds, then drop quickly back to normal idle.
I am struggling to figure out what is causing this temporary stick. I am lucky to have a breakout box, so I was checking various sensors while reproducing this behavior, and I only found that the Spark output (timing?) Was changing during this behavior.
TPS voltage range is within spec. EGR holds vaccuum. Throttle body is clean.
Overall idle vacuum is low though - 12in mercury.
I am wondering if the throttle plate screw is open too much, letting too much air in which in turn is decreasing my vaccuum, yet the idle is still OK because the computer is compensating correctly (perhaps by decreasing the IAC duty cycle?). The timing change delay is confusing to me though, it's almost like the computer's got a delayed reaction when switching from Part-throttle strategy, and warm idle strategy. (Assuming that me tapping the gas is what EEC-IV would cosider part-throttle strategy, and me off the gas (throttle plate closed) is warm idle strategy.
Saturday, October 16th, 2010 AT 6:04 PM