bad idle/upper misfire
03-25-10, 10:52 PM
#1
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bad idle/upper misfire
i picked up a 90 vert, auto.
125k mileage
2nd gear is slow shifting, like riding a clutch
problems
idle, idle will bounce 1200-1600
if i rev it over 2000, it will idle smooth at 1050 for a few seconds then start surging again
if i hold the rpms at anything below 4200 it has a even pop, pop, pop, pop in the exhaust
all plugs and wires have been replaced
any ideas?
125k mileage
2nd gear is slow shifting, like riding a clutch
problems
idle, idle will bounce 1200-1600
if i rev it over 2000, it will idle smooth at 1050 for a few seconds then start surging again
if i hold the rpms at anything below 4200 it has a even pop, pop, pop, pop in the exhaust
all plugs and wires have been replaced
any ideas?
03-25-10, 11:46 PM
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03-26-10, 11:24 AM
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03-26-10, 12:08 PM
#7
Also check the air intake piping for leaks upstream of the AFM. Unmetered air leaking into the piping can cause rough idle since the ECU is not accounting for the added air when setting the fuel input. You may have to pull the AFM, fashion an adapter/plug out of a PVC plug for the opening and pressurize the piping. That will quickly tell you if there is a leak, but don't pressurize to more than a few psi. And when you do, stand back, 'cause if the piping is sealed, the plug may just come flying out.
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03-26-10, 01:39 PM
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Also check the air intake piping for leaks upstream of the AFM. Unmetered air leaking into the piping can cause rough idle since the ECU is not accounting for the added air when setting the fuel input. You may have to pull the AFM, fashion an adapter/plug out of a PVC plug for the opening and pressurize the piping. That will quickly tell you if there is a leak, but don't pressurize to more than a few psi. And when you do, stand back, 'cause if the piping is sealed, the plug may just come flying out.
05-03-10, 11:13 AM
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05-03-10, 11:31 AM
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That hiss you are hearing is not normal, and could be a vacuum leak. Did you check the hoses and fittings going to the power brake booster? It's on that side... if it is leaking internally, you might not find it with the carb cleaner test. Try pulling the hose to the brake and capping it temporarily, see if the hiss goes away... look also at the hoses for the BAC valve and AWS solenoid; they are also fairly large and could be a source of a leak.
05-03-10, 01:03 PM
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That hiss you are hearing is not normal, and could be a vacuum leak. Did you check the hoses and fittings going to the power brake booster? It's on that side... if it is leaking internally, you might not find it with the carb cleaner test. Try pulling the hose to the brake and capping it temporarily, see if the hiss goes away... look also at the hoses for the BAC valve and AWS solenoid; they are also fairly large and could be a source of a leak.
05-03-10, 07:04 PM
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well i may have just solved my problem. im over to baltimore MD weds to buy a wrecked 88 vert, its "good running" and 5 speed, ill just make sure it runs good before i buy it, and do a 5 speed swap while i switch motors
05-03-10, 07:35 PM
#16
talk about tossing parts to fix the problem, you have an intake leak and if you look hard it won't take long for you to fix it (confirmed by you spraying carb cleaner around the intake area and engine dies down). If your current engine is in good condition (compression wise) i don't see a need to swap a perfectly good engine out, besides the transmission part. The swap is going to take a lot of your time, if you thought this was hard, be prepared for it.
05-03-10, 07:45 PM
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talk about tossing parts to fix the problem, you have an intake leak and if you look hard it won't take long for you to fix it (confirmed by you spraying carb cleaner around the intake area and engine dies down). If your current engine is in good condition (compression wise) i don't see a need to swap a perfectly good engine out, besides the transmission part. The swap is going to take a lot of your time, if you thought this was hard, be prepared for it.i know i have to do the conversion, but i will have all the parts and tools i need at my disposal, minus a lift...
the car isnt a DD atm anyway, no tags either. the auto trans is basically bad, so would rather go ahead and swap it and be done then have it go out 1 month after fixing a leak and being legal.
i have to find the compression gauge, i still have yet to do a compression check.
also, the OMP is failing on this motor anyway
atleast its thrown a code for OMP twice (got 2 stoke oil in gas fyi)
05-03-10, 07:48 PM
#18
would it not be easier to swap transmission in 1 foul swoop, skipping the part of seperating motor and trans in both cases, and swapping the flywheel etc?
i know i have to do the conversion, but i will have all the parts and tools i need at my disposal, minus a lift...
the car isnt a DD atm anyway, no tags either. the auto trans is basically bad, so would rather go ahead and swap it and be done then have it go out 1 month after fixing a leak and being legal.
i have to find the compression gauge, i still have yet to do a compression check.
also, the OMP is failing on this motor anyway
atleast its thrown a code for OMP twice (got 2 stoke oil in gas fyi)
i know i have to do the conversion, but i will have all the parts and tools i need at my disposal, minus a lift...
the car isnt a DD atm anyway, no tags either. the auto trans is basically bad, so would rather go ahead and swap it and be done then have it go out 1 month after fixing a leak and being legal.
i have to find the compression gauge, i still have yet to do a compression check.
also, the OMP is failing on this motor anyway
atleast its thrown a code for OMP twice (got 2 stoke oil in gas fyi)
05-03-10, 08:27 PM
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You have a code for the OMP and you are wondering why the car is misfiring and not running well??? The 2 stroke oil will not help anything, and you must be very lucky the OMP has not fried the ECU yet if it is really bad. If the transmission is bad, then I would say yes, much easier to just go ahead and swap everything out in that case. Sounds like you have more than just an intake leak now that you mentioned this, so that new engine with transmission will be the best way to go if you have easy access to it...
05-03-10, 11:43 PM
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the hiss IS on the driver side, but its not even near the brake booster, its close to the power steering pump, thats why i was thinking the pump was noisy. i sprayed carb cleaner on every hose to no avail, but when i sprayed anywhere near or on the intake mani it dies down a bit
talk about tossing parts to fix the problem, you have an intake leak and if you look hard it won't take long for you to fix it (confirmed by you spraying carb cleaner around the intake area and engine dies down). If your current engine is in good condition (compression wise) i don't see a need to swap a perfectly good engine out, besides the transmission part. The swap is going to take a lot of your time, if you thought this was hard, be prepared for it.where i sprayed is NOT the intake...
borrowing a users picture
i sprayed under the intake. in the center of this picture is where i was spraying in actuality
05-04-10, 12:08 AM
#21
Looks like my engine bay when I had the car running!!! (hehe it is...)
You still sprayed the intake area, in the picture you can see the lower intake manifold (with the paper towels plugging it). Your intake gaskets are probably bad along with the OMP. Someone probably removed it and didn't replace it properly?
It could be that, or the grommets on the fuel injectors are leaking air or the grommets are missing all together? Or some of the hoses on the vacuum spider (the red silicone hoses in my picture) are not hooked up (those are under the intake, right next to the lower intake manifold, or the ones closer to the drivers side too)...
You still sprayed the intake area, in the picture you can see the lower intake manifold (with the paper towels plugging it). Your intake gaskets are probably bad along with the OMP. Someone probably removed it and didn't replace it properly?
It could be that, or the grommets on the fuel injectors are leaking air or the grommets are missing all together? Or some of the hoses on the vacuum spider (the red silicone hoses in my picture) are not hooked up (those are under the intake, right next to the lower intake manifold, or the ones closer to the drivers side too)...
05-04-10, 12:26 AM
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Looks like my engine bay when I had the car running!!! (hehe it is...)
You still sprayed the intake area, in the picture you can see the lower intake manifold (with the paper towels plugging it). Your intake gaskets are probably bad along with the OMP. Someone probably removed it and didn't replace it properly?
It could be that, or the grommets on the fuel injectors are leaking air or the grommets are missing all together? Or some of the hoses on the vacuum spider (the red silicone hoses in my picture) are not hooked up (those are under the intake, right next to the lower intake manifold, or the ones closer to the drivers side too)...
You still sprayed the intake area, in the picture you can see the lower intake manifold (with the paper towels plugging it). Your intake gaskets are probably bad along with the OMP. Someone probably removed it and didn't replace it properly?
It could be that, or the grommets on the fuel injectors are leaking air or the grommets are missing all together? Or some of the hoses on the vacuum spider (the red silicone hoses in my picture) are not hooked up (those are under the intake, right next to the lower intake manifold, or the ones closer to the drivers side too)...
nothing has been removed before, i bought this car, it was brought into the shop 2 years ago to fix a oil leak and exhaust leak. guy disappeared.
car sat in lot for 2 years. he showed back up, and i bought the car for $300.
still has leak, though i suspect not oil as its not loosing any as far as i can tell., atf was 1 qt low when i got it
05-04-10, 12:32 AM
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