1992 Voyager 3.3 Liter V6. Starts OK, Will Idle for about a minute or two until stalls as the IAC opens and the motor can not respond appropriately/ accordingly. No distinct detectable miss at idle , just struggles to keep idling, notable heavy modulation of IAC trying to maintain idle, application of throttle brings about severe misses /missing, pops and sputters, intake back fire indicative of over lean condition at just barely above idle, very hard to gain any engine speed/ rpm as throttle valve is opened. IF the engine does manage to get above 2000 to 2500 RPM ( estimated because there is no tachometer to use for reference) THEN engine instantly smooths out and runs normally /revs aggressively in high contrast to horrible stumble in region of just above idle to 2000 RPM.
(I admit that I already did the part swapping gambler approach that you do not like, with no remedy on my part) Already changed TPS (new) no remedy, took it back (Thanks local national chain auto parts store), MAP Sensor replaced (used from Wrecking yard) no remedy, and ECM replaced ( used unit from wrecking yard) no remedy. No change in problematic running condition noted as mentioned parts were replaced. Checked for vacuum leaks in area of Throttle body with unlit propane torch, no effect noted. Contemplated EGR problem. Checked engine for EGR. Apparently this engine does NOT have an EGR system. At this point wondering about any possible IAC issues / suspect of Junk Yard MAP. I tried replacing the mentioned parts, with no success. Seeking outside input at this point before proceeding any further. Can a faulty Fuel Pressure Regulator cause that kind/ degree of problem? I am doubting it. Due to the way that an FPR works a failing FPR would tend to keep fuel pressure higher than needed causing an overly rich condition. Can a faulty O2 sensor cause that degree of problem? I am doubting it. since O2 sensor is supposed to fine tune A/F ratio once the motor goes into closed loop operation. Crank Evac check valve ? I am doubting it. Anything else ? Thanks in advance.
UPDATE I hooked up a Multi Meter to the wiring leads for the MAP sensor while still installed on engine. It showed appropriate 5 volts supplied to the sensor. 4 volts at signal wire with engine not running but key on. Idling 1.5 volts, 2.5 volts shown on throttle blips. I did not take the engine into the RPM range where it smooths out and runs well, so no Signal Volt reading there. Maybe I should have. Problem still exists, even as the MAP sensor appears to be functional as tested. At very least MAP is not completely dead as it does show a response to changing conditions.
At the recommendation of a mechanic friend, I took the upper intake manifold off to inspect wiring. No frayed wires were found. Now I have to re wrap the wiring. I do not think it is wiring, because a wiring short would not magically resolve itself above 2000 RPM and consistently cause problems in the mentioned troublesome RPM. A troublesome wiring short would act up perhaps intermittently but at ALL RPM levels. This problem is VERY consistent. It appears to be a lean out condition in the problematic RPM range. I think it is an electronic component failure issue because it is so consistent at causing the lean out condition in the problematic RPM range. There are only so many major sensors/ electronic EFI components. I have been through them. I am wondering If the ECM that I got from the wrecking yard is bad with the very same malfunction that the original one has, so I have ended up with two bad ECM's as this is some common place rampant malfunction on Chrysler corp ECMs for this model. Heard about anything like that ? The original ECM completely failed several years, even though ECM's are supposedly the most reliable component in an EFI system and supposedly bullet proof. Any feed back / ideas? Thanks in advance !