Hi!
I have 1997 Chevrolet Blazer AT 4x4, has approx. 140000 miles on it. There is a problem: when the car warms up, it starts idling rough, sometimes stalls. The car always starts easy, even at temperatures way below freezing. When cruising - engine rpm (when below 2000) not constant. So when cruising on the highway at 50 mph, the tranny goes into lockup, and rpms drop to 1500. After driving for a while on lockup at 50-60 mph(sometimes feel vibration). Then TCC lockup disengages, and lockup doesn't occur again. If i drive long enough like this p1870 appeares, tranny starts to shift hard. I actually just got the transmission completely rebuilt, with lots of parts changed, incluiding valvebody (spent almost $2000), so it was not because of the transmission, the problem remained. Also replaced spark plug wires, rotor, cap, fuel pump (it died completely, replaced whole assembly), engine coolant tempereture sensor, tried to find a vacuum leak- couldn't. I desided that it is enough of mindless parts changing, i should really find a problem.
Bought a bluetooth scanner for an android phone, started monitoring data, noticed that one of the O2 sensor's signals disappeares, for a second, then returns. So, i replaced this O2 sensor- didn't fix the problem(O2 sensors readings seem normal now).
Fuel trim is within -8 +8 range. Car throws no codes (except for p1870). When monitoring data on scanner noticed that ignition timing wobbles fast from 15 to 21 randomly at idle. If i press the gas pedal the ignition timing goes to -5 or 0 quick, then shows 34-35ish and the car hesitates during acceleration. So for the ignition timing to remain constant, i need to press the gas pedal more than 15-20% with rpms around 2000 or more. Throttle position sensor reading seems alright -as far as i can judge. How do You think, what should i check next?
Thanks