1992 LT-1 rough idle, pinging/knocking
#1
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Member Since: Jul 2001
Location: cape coral, fl. USA Florida
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Engine starts fine strong. then rough idle.
When in drive, I get rough idle, almost stalling to 1200rpm.
(remove IAC valve connector, runs smooth,
but high rpm's)
reconnect IAC valve,then when driving,
Acceleration I get pinging/knocking, greater with more throttle.
When running steady 50mph, I get stumbling, hesitation
When coasting, its almost bucking!
Replaced opti-spark, plugs, wires and water pump.
Tested fuel pressure 42lbs before engine start, 39 when running at idle.
all injectors drop engine speed about 50rpm when disconnected.
cleared fault codes, and nothiing new shows up.
Question: WHAT HAVE I MISSED??????
When in drive, I get rough idle, almost stalling to 1200rpm.
(remove IAC valve connector, runs smooth,
but high rpm's)
reconnect IAC valve,then when driving,
Acceleration I get pinging/knocking, greater with more throttle.
When running steady 50mph, I get stumbling, hesitation
When coasting, its almost bucking!
Replaced opti-spark, plugs, wires and water pump.
Tested fuel pressure 42lbs before engine start, 39 when running at idle.
all injectors drop engine speed about 50rpm when disconnected.
cleared fault codes, and nothiing new shows up.
Question: WHAT HAVE I MISSED??????
#3
Le Mans Master
You need to hook up a code scanner to see what the engine is doing. Also take another look at your spark plugs. See if the engine is running lean (possible clogged fuel filter). What is the reading from the throttle position sensor?
#5
Melting Slicks
Some possible culprits:
- Faulty IAC valve
- Bad EGR valve
- Spark plugs not fully seated in head
- Plug wires not on Opti in correct order
- Carbon-coated 02 sensors (Mine has 3)
- Clogged fuel filter
- Faulty IAC valve
- Bad EGR valve
- Spark plugs not fully seated in head
- Plug wires not on Opti in correct order
- Carbon-coated 02 sensors (Mine has 3)
- Clogged fuel filter
#6
How about squirting some Throttle body cleaner in the IAC's air passage hole with the engine off and the IAC removed? If it got better with the max air bypass (IAC removed),maybe you've got a varnish problem in the air bypass circuit of the throttle body. If you remove the IAC's electrical connection with the motor running you have to reset the ECM after reconnection via a procedure described in the official service manual.