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:dunno: I have been trying to solve this problem since Early March, and now all I can do is scratch my head... hoping someone here can offer some advice.
Car is my 1990 Oldsmobile Trofeo, Buick 3800 LN3 motor (vin c).
I drive the car daily and every morning it starts up great, and idles normally (625 RPMS once warm). However, sometimes later in the day, the car will start and my RPMS will be at 1500 at idle. When this happens, the car still runs good, but just a little rougher. The biggest problem with it is that the car does not downshift at the correct points since the shift points are driven by the Throttle Position, and when coming to a stop the car jerks from second down to first at the last minute. If I have my foot OFF the gas, the car will just cruise as if Im at partial throttle, even though the TPS is reading closed throttle. The next morning, start the car and shes back to normal.
If I unplug the battery for 15 mins for the ECM reset, the issue will go away for a couple of days, but it always comes back.. Ive noticed it comes back moreso when moisture is involved (car wash, rain).
In my endeavor to solve, I have replaced the following, in this order:
Im really at a loss as to where I should go next. Im thinking my ECM may be bad. My INT fuel readings are 128, so my vacuum leak/lean issue is pretty much fixed.
I also have access to live ECM data with this car, and can take an ECM snapshot at speeds on the highway. If any ECM data will help diagnose the issue, please let me know and I can provide. One thing I can note is that, while my TPS usually shows .44 volts at closed throttle, sometimes I will notice it down at .42, and sometimes itll even fluctuate between .40 and .42. Wondering if maybe my TPS is faulty, or even just loose. Once the ECM reads the .40, that then would become the baseline for closed throttle. WHen it adjusts up to .44, it thinks the throttle open????
Car is my 1990 Oldsmobile Trofeo, Buick 3800 LN3 motor (vin c).
I drive the car daily and every morning it starts up great, and idles normally (625 RPMS once warm). However, sometimes later in the day, the car will start and my RPMS will be at 1500 at idle. When this happens, the car still runs good, but just a little rougher. The biggest problem with it is that the car does not downshift at the correct points since the shift points are driven by the Throttle Position, and when coming to a stop the car jerks from second down to first at the last minute. If I have my foot OFF the gas, the car will just cruise as if Im at partial throttle, even though the TPS is reading closed throttle. The next morning, start the car and shes back to normal.
If I unplug the battery for 15 mins for the ECM reset, the issue will go away for a couple of days, but it always comes back.. Ive noticed it comes back moreso when moisture is involved (car wash, rain).
In my endeavor to solve, I have replaced the following, in this order:
- Delphi TPS, adjusted within spec
- PCV Valve
- Bosch Oxygen Sensor
- Fuel Filter
- Brand New MAF
- TPS Pig-tail connector
- AC Delco Oxygen Sensor (was hoping the Bosch was bad)
- Throttle Body gasket and EGR Adapter Gasket (to fix vac leak)
Im really at a loss as to where I should go next. Im thinking my ECM may be bad. My INT fuel readings are 128, so my vacuum leak/lean issue is pretty much fixed.
I also have access to live ECM data with this car, and can take an ECM snapshot at speeds on the highway. If any ECM data will help diagnose the issue, please let me know and I can provide. One thing I can note is that, while my TPS usually shows .44 volts at closed throttle, sometimes I will notice it down at .42, and sometimes itll even fluctuate between .40 and .42. Wondering if maybe my TPS is faulty, or even just loose. Once the ECM reads the .40, that then would become the baseline for closed throttle. WHen it adjusts up to .44, it thinks the throttle open????
