91'L98 sluggish performance
Thread Starter
1st Gear
Joined: Aug 2006
Posts: 1
Likes: 0
91'L98 sluggish performance
newbie here. Bought this vette (91'L98conv.)six months ago and felt it didnt perform at all like my 95 Lt1, wasnt expecting it to either until I got an 87also L98 and that thing runs great.All cars are basically stock. the 91 doesnt seem to idle very smoothly and isnt very responsive at the throtle .It feels a little shaky at idle, surges up and down between 900 and 1000 rpm.My question is where to start Ive checked half the plugs the ones easiest to get to and all were quite clean.I am not sure if I have a miss or a vacuum leak or bad injectors.Ive read some forums stating that the injectors back then were prone to corrosion because of ethanol and that the corrosion is irreversible.Also my oil pressue gage has eratic readings sometimes reading normal and sometimes bouncing up and down like a sizemograph . SYS also flashing mabey because the gage is malfunctioning . Ive changed the oil sending unit but no change. Anyway any help would be appreciated.Car has 78K on it.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
poor driveability
sounds like vacuum leaks but could be more
check the vacuum lines to the map sensor. poor hoses may let in 2 much air, giving the computer weak signals from the map sensor.
900-1000 is pretty high.
check for a stuck pcv valve, bad cruise control check valve, and bad vacuum line to the fuel evap cannister.
also a bad idle air control valve or a dirty IAC plate not letting the IAC valve seat well.
could be bad plastic tubing under the plenum, bad hoses at the cruise control.
take the passenger side under dash closeout panel off, and listen for vacuum leaks under the computer.
get a syringe at the drug store, put 6 inches of vacuum hose on it and fill it with gas.
drip about 3 drops on the bottom orings at the base of the injectors. if the idle chages, they need replacing.
check the vacuum lines to the map sensor. poor hoses may let in 2 much air, giving the computer weak signals from the map sensor.
900-1000 is pretty high.
check for a stuck pcv valve, bad cruise control check valve, and bad vacuum line to the fuel evap cannister.
also a bad idle air control valve or a dirty IAC plate not letting the IAC valve seat well.
could be bad plastic tubing under the plenum, bad hoses at the cruise control.
take the passenger side under dash closeout panel off, and listen for vacuum leaks under the computer.
get a syringe at the drug store, put 6 inches of vacuum hose on it and fill it with gas.
drip about 3 drops on the bottom orings at the base of the injectors. if the idle chages, they need replacing.
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
What do you mean by "basically stock??"
First thing im going to suggest is look for a loose ground. Then look for a dirty ground. Then replace the battery, and make sure the terminals are perfectly clean.
Check the alternator output, (not with the guage on the dash)
Check the coolant temp sensor,
Check the intake air temp sensor.
Check the fuel pressure and see if it holds when you shut the engine off.
Check the fuel pump relay and make sure the wires connected to it are in good shape
Check all that stuff CoupeGuy says ubove.
Pull the throttle body off and clean it out.
Check and reset the minimum air flow stop screw in the throttle body.
Check and adjust the TPS
Let us know what happens with all that.
First thing im going to suggest is look for a loose ground. Then look for a dirty ground. Then replace the battery, and make sure the terminals are perfectly clean.
Check the alternator output, (not with the guage on the dash)
Check the coolant temp sensor,
Check the intake air temp sensor.
Check the fuel pressure and see if it holds when you shut the engine off.
Check the fuel pump relay and make sure the wires connected to it are in good shape
Check all that stuff CoupeGuy says ubove.
Pull the throttle body off and clean it out.
Check and reset the minimum air flow stop screw in the throttle body.
Check and adjust the TPS
Let us know what happens with all that.
