1995 LeSabre 3.8L V6 - P0122/P0123 and racing

dpgmfixer

Member
Hi,
I have an ongoing problem with my 1995 Buick LeSabre 3.8L V6. It starts up cold racing and eventually settles down to an intermittent slow/fast (but not racing) idle. I have a check engine light with codes P0122 (TPS signal low) and P0123 (TPS signal high). Last year I put in a new TPS and MAP sensor which help for a while but the problem came back so my mechanic checked it out and put in a second TPS which has also helped for a while but the problem is back again. When driving the car, the idle will eventually kick back up into a very fast racing, requiring heavier than usual breaking to stop. I have to pull over, shut the car off and wait for a minute before turning it back on. I’m suspecting that I either have a bad TPS connector, a crack in the wiring somewhere, or an issue with the computer. Below is the Engine Group 1 & 2 diagnostics. Any thoughts/help would be appreciated.

Thanks
Dave.

Codes
P0122 TPS Signal Low
P0123 TPS Signal High

Engine Group 1


Gear 2,3,4 SW OFF
AC CL OFF
AC Head Press NORM
AC Request OFF
Batt (V) 13.8
LT Fuel Trim 125
LT Fuel TR CL 0
Boost % 0.0
CC Brake SW OFF
CC On/Off SW ON
CC Res/Acc SW OFF
CC Servo % 0
CC SET MPH 0
CC SET/CST SW OFF
CC Servo Req % 0
EVAP Duty % 13
EVAP Solenoid ON
MIL ON
Coolant 199
EGR Req % 0
EGR VLVPOS % 0
EGR VLvPOS (v) .7
KS Counter 12
Exhaust02 Rich
Fuel Cutoff NO
IAC Pos 35
IDLE REQ RPM 750
INJ PW(ms) 3.6
ST Fuel Trim 12
Knock Ret 0
LOOP STAT CLSD
MAF gr/s 5
IAT degF 60
O2S (mv) 100-800
PNP Switch P/N
PROM ID 1694
Spark Adv 11
TCC Applied NO
TCC Brake SW OFF
TCC Duty Cyc % 0
TCC Slip RPM 255
TCC Solenoid OFF
Throttle % 0 -2
TPS Sensor (v) .73 - 1.22
Trans Temp 94

Engine Group 2
CAT Failed 0
cat Passed 0
CYL 1 - 6 Misfire NO
cYLS Passed / Failed 0
MAP Failed 2
MAP Passes 0
RPM Failed 0
RPM Passes 6
Turbine RPM 0
 
while i suppose the TPS sensor / electrical can be a problem, have you taken apart and cleaned the throttle body and associated parts?

the throttle blade will pick up grime and dirt which will interfere with the closed throttle position, not allowing the blade to seat properly ( too much air bypassing ) and it can also get into the idle bypass, not allowing sufficient air in the proper direction.

you can often fix start / idle issues with a can of carb cleaner and some brushes, wires, picks, in order to thoroughly clean the internals of the throttle body.

spray some electrical contact cleaner into the TPS ( which is normally just a rheostat or variable resistor ) and work it as well.

if this doesn't fix the issue, you may want to go through and start cleaning / verifying your electrical connectors to make sure that none of them have started getting burnt.

normal failure mode for these multi pin connectors is that they start getting a bit of corrosion on them
then they stop conducting so well
then they start building excess heat in order to get current across the poor connection
then they start melting the plastic connector back
which makes the pin have an even worse connection
which causes even more heat.
til they don't work any more.


so when you pull a connector apart, you'll find one or more pins to be severely melted back.

chasing electrical faults with all these wires can be a huge pain in the *** though.
 
Good idea Bob, another issue I've seen is the IAC valve. Had several come thru our service department with high idle problems that traced back to the idle air control valve. Just food for thought.
 
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