rough idle and pinging
09-14-2001, 11:00 AM
#1
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Car: 90 IROC 5.7 hardtop
Engine: L98
Transmission: T5 swap
Axle/Gears: Yup -- they still work
rough idle and pinging
Hi All,
I have a '91 Formula LB9 TPI 5-speed with about 45k on the car and motor. Recently I've had some drive-ability issues fixed at the GM dealer, ended up with new plug wires and distributor, O2 sensor replaced. This helped alot (the car was in storage for 3 years) but a couple of weeks ago I developed a rough idle.
The engine shakes at idle but otherwise goes as fast as ever pulling strong to redline in each gear. My gas milaeage has dropped dramatically and the car shakes and bucks if I leave the clutch in till the last minute when stopping at a light (it didn't used to do this).
The shake at idle is very noticeable but not radical, in other words it is very irritating but I can live with it for now. I figured I'd go back to the GM dealer but these guys always seem to fix 1/2 the problem but charge me twice what it is worth.
One more thing, the engine pings alot under load now. When I hit the gas in say 3rd gear, it pings then abruptly stops pinging. The whole time the car accelerates well. I don't see any colored exhaust coming out of the pipes -- it looks normal. Also, at tip-in, when you just touch the gas, the engine hesitates or stumbles and has a slight mis-fire.
Any ideas ? Any of you guys seen this before ?
Thx in advance, RP.
I have a '91 Formula LB9 TPI 5-speed with about 45k on the car and motor. Recently I've had some drive-ability issues fixed at the GM dealer, ended up with new plug wires and distributor, O2 sensor replaced. This helped alot (the car was in storage for 3 years) but a couple of weeks ago I developed a rough idle.
The engine shakes at idle but otherwise goes as fast as ever pulling strong to redline in each gear. My gas milaeage has dropped dramatically and the car shakes and bucks if I leave the clutch in till the last minute when stopping at a light (it didn't used to do this).
The shake at idle is very noticeable but not radical, in other words it is very irritating but I can live with it for now. I figured I'd go back to the GM dealer but these guys always seem to fix 1/2 the problem but charge me twice what it is worth.
One more thing, the engine pings alot under load now. When I hit the gas in say 3rd gear, it pings then abruptly stops pinging. The whole time the car accelerates well. I don't see any colored exhaust coming out of the pipes -- it looks normal. Also, at tip-in, when you just touch the gas, the engine hesitates or stumbles and has a slight mis-fire.
Any ideas ? Any of you guys seen this before ?
Thx in advance, RP.
09-15-2001, 12:38 PM
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My car has some of the same problems. They all tell me to check the IAC, TPS, and fuel system (relay, pump...). I think my problem is the CTS though. Does your "Service Engine Soon" light come on? If it does try pulling your codes. It should tell you exactly what is wrong.
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1988 305 TBI camaro. Flowmaster exhaust, K&N air filter, complete IROC-Z makeover (stripes, ground effects, interior...etc), kenwood c.d. player.
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1988 305 TBI camaro. Flowmaster exhaust, K&N air filter, complete IROC-Z makeover (stripes, ground effects, interior...etc), kenwood c.d. player.
09-17-2001, 08:09 AM
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Car: 90 IROC 5.7 hardtop
Engine: L98
Transmission: T5 swap
Axle/Gears: Yup -- they still work
Thx for the reply. I've been stuck with this for awhile neither GM or the tech boards offered any help.
My Formula has very low mileage, about 48k miles or 68k kilometers (Canadian eh ?). I've swapped the IAC, no effect. had the TPS and IAC calibrated, no effect. Replaced the O2 sensor, no effect. The car seems to know when to go to 'closed loop' (cpu switches to reading off the O2 sensor) so I think the CTS is functioning correctly.
Got desperate and replaced the plug wires and 1/2 the spark plugs (couldn't get to the passenger side because of the A/C what a tight squeeze). But the plugs I replaced didn't really need replacing so I'm in no hurry to finish the task.
Last night I switched my 180 degree thermostat to the factory 195. That changed a few things. The car idles alot more smoothly now at running temperature. Previously it would really shake and rattle. It has calmed down ALOT -- draw some conclusions off that.
The car still has a shake at idle and pings under load (I use 94 octane gas), yet as far as I am concerned still delivers 230hp and 300lbs torque under WOT. The car goes like stink.
I noticed that I have developed an oil leak on my manifold (mid-section) but the leaks appear to be too distant from the intake ports to be contributing to a vacuum leak (although this would explain the 'idle shake'). I'll have to watch for surges in power under load which is a common sign of a vacuum leak.
I get no codes, the car scans clean from the outset and still scans clean. I replaced my fuel filter a couple of months ago and at that time the system pressure was correct. Haven't had any advice to check the fuel delivery system (yet) and doubt I will seeing as the car makes alot of power -- I can pull 5500rpm without any problems.
I may try having the injectors purged this weekend. I'll post the results.
Thx, RP.
My Formula has very low mileage, about 48k miles or 68k kilometers (Canadian eh ?). I've swapped the IAC, no effect. had the TPS and IAC calibrated, no effect. Replaced the O2 sensor, no effect. The car seems to know when to go to 'closed loop' (cpu switches to reading off the O2 sensor) so I think the CTS is functioning correctly.
Got desperate and replaced the plug wires and 1/2 the spark plugs (couldn't get to the passenger side because of the A/C what a tight squeeze). But the plugs I replaced didn't really need replacing so I'm in no hurry to finish the task.
Last night I switched my 180 degree thermostat to the factory 195. That changed a few things. The car idles alot more smoothly now at running temperature. Previously it would really shake and rattle. It has calmed down ALOT -- draw some conclusions off that.
The car still has a shake at idle and pings under load (I use 94 octane gas), yet as far as I am concerned still delivers 230hp and 300lbs torque under WOT. The car goes like stink.
I noticed that I have developed an oil leak on my manifold (mid-section) but the leaks appear to be too distant from the intake ports to be contributing to a vacuum leak (although this would explain the 'idle shake'). I'll have to watch for surges in power under load which is a common sign of a vacuum leak.
I get no codes, the car scans clean from the outset and still scans clean. I replaced my fuel filter a couple of months ago and at that time the system pressure was correct. Haven't had any advice to check the fuel delivery system (yet) and doubt I will seeing as the car makes alot of power -- I can pull 5500rpm without any problems.
I may try having the injectors purged this weekend. I'll post the results.
Thx, RP.
09-17-2001, 12:48 PM
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Car: 90 IROC 5.7 hardtop
Engine: L98
Transmission: T5 swap
Axle/Gears: Yup -- they still work
Good idea on the timing. I have been wondering if it was out ? Figured the ECM would compensate if it was. This assumes the base timing was in fact correct ?
The distributor was replaced in June/01, maybe GM messed up the initial or the tie-down bolt came loose ? In any event thanks for the reminder, I'll get it checked.
have a nice day.
The distributor was replaced in June/01, maybe GM messed up the initial or the tie-down bolt came loose ? In any event thanks for the reminder, I'll get it checked.
have a nice day.
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