1997 Chevrolet Cavalier LS running rich/lean

Asked by Oct 11, 2015 at 03:41 PM about the 1997 Chevrolet Cavalier

Question type: Maintenance & Repair

Hello, I have a 1997 Chevrolet Cavalier 2.2 with 155k that has been
running a crazy trim ratio. When the car is first started, which is starts fine
now that I replaced the MAP, TPS, IAC valve, EGR, Coil packs, spark plugs
and wires, battery, ignition lock cylinder, cleaned up ECM connects.
However when the car is first started, it runs open with a STFT of anywhere
from 0.0 to around 7.6 which fluctuates, but as soon as I push on the gas
pedal, the car switches over to closed loop (engine has just started and is
cold) and starts running rich from 0.0 to as much as -14.06 for STFT. The
LTFT is -7.6 and can go as far as -18.76 but never positive. The short term
usually will go from -1.6 to -2.8 initially during closed loop but will change
while driving from -12.6 to 4.6. My guess is a bad upstream 02 sensor
because of the age and mileage of the car, but I was wondering of other
possible causes?  The car has no signs of bad head gasket, normal
compression, coolant pressure test was fine, starts fine cold and great at
operating temperature but cranks for two seconds after cooling down then
trying to start it again. The car idles from 946 to 1068 rpms but runs at
normal rpm when given gas, when WOT and off, car will drop to standard
idle of 600 rpm but vibrate slightly rough and return to 1000 rpm when hot
or cold and has a load around 29-32.01%. Also for anyone thinking its a
MAF sensor, don't leave an answer, this car doesn't have one. Also a
shredder valve for the fuel rail -_-.

4 Answers

Also to note, only code is a P0507 which doesn't help -_-. No obvious signs of vacuum leaks found by myself or a shop. Only known one is post upstream 02 sensor at the connection pipe of the exhaust manifold and pipe, 1 inch down from the sensor. The darn thing keeps destroying gaskets and won't stay snug. It's a very small leak though that cannot be heard but seen when its very cold outside (talking about the pipe connection with two bolts, had to use lock washers to hold the wiggling bugger).

7,215

how is the thermostat? is it going to operating temps? 195-205 degrees?

Thermostat went bad after coolant change, causing thermostat to stick close and push coolant out of overflow or move like a slow metronome between 185-230 (problem with engine occurring before this), thermostat was changed (problems still persisted unaffected after). This car I believe has two thermostats but car functions correctly in terms of cooling system staying at 195.

the car had a previous history of misfires due to coil packs, timing tensioner and map which are now fixed, and wondering if that could have damaged the o2 sensor considering they operate by chemical reactions. IMPORTANT: One symptom I forgot to mention is the car when shifting down at 45 mph coasting, will cause the rpm to go down to 1000 rpm then up to 1500 rpm and repeat a couple of times causing surging. The car seems to also run rough then smooth then rough constantly.

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