Rough/low idle and a misfire code
10-19-2017
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Rough/low idle and a misfire code
its a 98 civic, automatic.. It idles very rough and shaky, when started, slowing down, at stops, etc etc.. the tachometer in the dash cluster shows it at around the 500 mark or so approximately when idling.. it however has not stalled at all, but kindof acts like its about to.. if i lightly touch the gas pedal, the idle evens out a bit and seems to stop the roughness/shaking at or around the 1k to 1.2k range... the top end appears to be just fine, the roughness goes away once i start driving and it drives quite smooth, although there seems to be a very slight/minor non-responsiveness or delay when accelerating, but barely noticeable.. the check engine light is on, and it does blink sometimes. the Only code that shows up is a cylinder 2 misfire..
As for the current/recent maintenance status, it has new plugs, wires, cap, and rotor, as well as new radiator and thermostat... Ive purchased carbon cleaner for the iac valve, and feeler gauges for a valve adjustment, but have not done them yet..
my gut would say that the idling issue and the misfire code are connected, however, the diagnosis/repair/troubleshooting process for either of those seem to be different from each other according to what ive been reading.. i'm not sure where to start or what to do, the car was purchased just a few days ago, and i need to pass the state inspection within 30 days... figured asking on a forum would shortcut the research process a bit.. quality input is much appreciated, and thanks in advance.
As for the current/recent maintenance status, it has new plugs, wires, cap, and rotor, as well as new radiator and thermostat... Ive purchased carbon cleaner for the iac valve, and feeler gauges for a valve adjustment, but have not done them yet..
my gut would say that the idling issue and the misfire code are connected, however, the diagnosis/repair/troubleshooting process for either of those seem to be different from each other according to what ive been reading.. i'm not sure where to start or what to do, the car was purchased just a few days ago, and i need to pass the state inspection within 30 days... figured asking on a forum would shortcut the research process a bit.. quality input is much appreciated, and thanks in advance.
10-19-2017
#2
OF top 99.5% creator (Formerly of the Puffinblunts variety)
Re: Rough/low idle and a misfire code
Check for vacuum leaks. Start with the vacuum line that runs from the cruise control to intake manifold.
10-19-2017
#3
If you think a good mechanic is expensive, try hiring a bad one
Re: Rough/low idle and a misfire code
It idles very rough and shaky,
. if i lightly touch the gas pedal, the idle evens out a bit and seems to stop the roughness/shaking at or around the 1k to 1.2k range...
the check engine light is on, and it does blink sometimes. the Only code that shows up is a cylinder 2 misfire..
. if i lightly touch the gas pedal, the idle evens out a bit and seems to stop the roughness/shaking at or around the 1k to 1.2k range...
the check engine light is on, and it does blink sometimes. the Only code that shows up is a cylinder 2 misfire..
the car was purchased just a few days ago,
You're about to find out WHY it was for sale. (It needs a whole lot of money thrown at it, that's why it was for sale.)
and i need to pass the state inspection within 30 days.
10-20-2017
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10-20-2017
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Re: Rough/low idle and a misfire code
Also, do a compression test as Ezone stated. If any of the cylinders are low during the dry compression test then repeat the compression test adding a teaspoon of oil (wet test) in the offending cylinder(s). If compression raises significantly after adding oil this points to compression ring sealing issue. If compression doesn't raise significantly after oil is added then it points to a potential intake/exhaust valve(s) leak or head gasket leak (if compression is low in two adjacent cylinders).
10-20-2017
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true, but hopefully it is being caught and dealt with soon enough.. The idle problem and code started after the last inspection. Considering the distributer cap is new, it could be a timing issue perhaps, ill be checking that too..
10-20-2017
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Also, do a compression test as Ezone stated. If any of the cylinders are low during the dry compression test then repeat the compression test adding a teaspoon of oil (wet test) in the offending cylinder(s). If compression raises significantly after adding oil this points to compression ring sealing issue. If compression doesn't raise significantly after oil is added then it points to a potential intake/exhaust valve(s) leak or head gasket leak (if compression is low in two adjacent cylinders).
10-20-2017
#8
If you think a good mechanic is expensive, try hiring a bad one
Re: Rough/low idle and a misfire code
it was inspected and passed a mere 3 months ago and i was provided with the inspection report..
This means almost nothing now that it has a problem.
It has had a bunch of uptodate parts and work done,
10-20-2017
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however, none of that really matters as it pertains to the topic at hand which is How to diagnose and fix the problems, not an exposé on whether it was worth purchasing.
10-20-2017
#10
If you think a good mechanic is expensive, try hiring a bad one
Re: Rough/low idle and a misfire code
Ok......not in any real order
I'd stab the gas pedal to the floor and crank it over (hope this cancels fuel injection so it can't start) OR disable the distributor or ecm so it can't run, then crank it several seconds while listening----this is a "relative compression test", I can usually HEAR if one cylinder is significantly different from the others..which may dictate a real compression test with a real tester.
With it running, I'd slowly lift the #2 plug wire up and listen for the snap noise of a strong spark making its way out the end of the wire down inside the plug tube.....that would tell me the spark is getting to the end of the plug wire at least.....AND note if the RPM drops or the engine load changes indicating that cylinder WAS contributing a little bit to running (i.e. not completely dead)
Grab a compression tester from a buddy or rent one from a parts store.....Pull out the spark plugs, see if the plug from the suspect cylinder (#2?) looks very different from the others (that's a bad sign).
Then do the compression test while the plugs are out.
If the #2 has good compression and the plug is clean and white, it might be a injector problem--no fuel getting injected into that cylinder for some reason OR it's lean at idle on that cylinder for some reason (vacuum leakage, manifold gasket blown, vacuum hose popped off somewhere, etc.).
I'd stab the gas pedal to the floor and crank it over (hope this cancels fuel injection so it can't start) OR disable the distributor or ecm so it can't run, then crank it several seconds while listening----this is a "relative compression test", I can usually HEAR if one cylinder is significantly different from the others..which may dictate a real compression test with a real tester.
With it running, I'd slowly lift the #2 plug wire up and listen for the snap noise of a strong spark making its way out the end of the wire down inside the plug tube.....that would tell me the spark is getting to the end of the plug wire at least.....AND note if the RPM drops or the engine load changes indicating that cylinder WAS contributing a little bit to running (i.e. not completely dead)
Grab a compression tester from a buddy or rent one from a parts store.....Pull out the spark plugs, see if the plug from the suspect cylinder (#2?) looks very different from the others (that's a bad sign).
Then do the compression test while the plugs are out.
If the #2 has good compression and the plug is clean and white, it might be a injector problem--no fuel getting injected into that cylinder for some reason OR it's lean at idle on that cylinder for some reason (vacuum leakage, manifold gasket blown, vacuum hose popped off somewhere, etc.).
10-20-2017
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Ok......not in any real order
I'd stab the gas pedal to the floor and crank it over (hope this cancels fuel injection so it can't start) OR disable the distributor or ecm so it can't run, then crank it several seconds while listening----this is a "relative compression test", I can usually HEAR if one cylinder is significantly different from the others..which may dictate a real compression test with a real tester.
With it running, I'd slowly lift the #2 plug wire up and listen for the snap noise of a strong spark making its way out the end of the wire down inside the plug tube.....that would tell me the spark is getting to the end of the plug wire at least.....AND note if the RPM drops or the engine load changes indicating that cylinder WAS contributing a little bit to running (i.e. not completely dead)
Grab a compression tester from a buddy or rent one from a parts store.....Pull out the spark plugs, see if the plug from the suspect cylinder (#2?) looks very different from the others (that's a bad sign).
Then do the compression test while the plugs are out.
If the #2 has good compression and the plug is clean and white, it might be a injector problem--no fuel getting injected into that cylinder for some reason OR it's lean at idle on that cylinder for some reason (vacuum leakage, manifold gasket blown, vacuum hose popped off somewhere, etc.).
I'd stab the gas pedal to the floor and crank it over (hope this cancels fuel injection so it can't start) OR disable the distributor or ecm so it can't run, then crank it several seconds while listening----this is a "relative compression test", I can usually HEAR if one cylinder is significantly different from the others..which may dictate a real compression test with a real tester.
With it running, I'd slowly lift the #2 plug wire up and listen for the snap noise of a strong spark making its way out the end of the wire down inside the plug tube.....that would tell me the spark is getting to the end of the plug wire at least.....AND note if the RPM drops or the engine load changes indicating that cylinder WAS contributing a little bit to running (i.e. not completely dead)
Grab a compression tester from a buddy or rent one from a parts store.....Pull out the spark plugs, see if the plug from the suspect cylinder (#2?) looks very different from the others (that's a bad sign).
Then do the compression test while the plugs are out.
If the #2 has good compression and the plug is clean and white, it might be a injector problem--no fuel getting injected into that cylinder for some reason OR it's lean at idle on that cylinder for some reason (vacuum leakage, manifold gasket blown, vacuum hose popped off somewhere, etc.).
10-31-2017
#12
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I completed a compression test.. and inspected the plugs and boots in the process.. Results are; plug #2 does indeed look different from the rest, it was brown with a little burnt oil on it.. the rest looked fine..
the compression results were; cylinder # 1 had 180 psi, cylinder # 2 (the misfiring one) had zero, no compression. cylinder # 3 had only 30 psi, very low, and cylinder # 4 had 155 psi.. I then did a "wet" compression test on the suspect cylinders, and it made no difference to compression..
so it appears # 1 and # 4 are fine. and compression on # 2 and # 3 are no and low... so 2 cylinders are bad, and one is dead.
i am aware that when it is more than 1 cylinder, it implies engine mechanical issues.. however some are eliminated and narrowed by the symptoms i have.. It runs and drives fine, except for the rough idle and hesitant start-up.. It does Not have a knocking sound at all indicative of a rod, and it does not appear to be overheating indicative of head gasket.. the plugs were not swimming in oil or fuel except for the appearance of burnt oil on #2. and the coolant looks fine, with no oil mixed in it.
What would be my next steps in the diagnosis and troubleshooting process now that i have results of the compression test and the rest of the indicators?
the compression results were; cylinder # 1 had 180 psi, cylinder # 2 (the misfiring one) had zero, no compression. cylinder # 3 had only 30 psi, very low, and cylinder # 4 had 155 psi.. I then did a "wet" compression test on the suspect cylinders, and it made no difference to compression..
so it appears # 1 and # 4 are fine. and compression on # 2 and # 3 are no and low... so 2 cylinders are bad, and one is dead.
i am aware that when it is more than 1 cylinder, it implies engine mechanical issues.. however some are eliminated and narrowed by the symptoms i have.. It runs and drives fine, except for the rough idle and hesitant start-up.. It does Not have a knocking sound at all indicative of a rod, and it does not appear to be overheating indicative of head gasket.. the plugs were not swimming in oil or fuel except for the appearance of burnt oil on #2. and the coolant looks fine, with no oil mixed in it.
What would be my next steps in the diagnosis and troubleshooting process now that i have results of the compression test and the rest of the indicators?
Last edited by A1ien; 10-31-2017 at 09:09 AM.
10-31-2017
#13
OF top 99.5% creator (Formerly of the Puffinblunts variety)
Re: Rough/low idle and a misfire code
With two cylinders with those compressions number this low I don't see how that is possible? At higher speeds it may smooth out but it's definitely not running optimal. Anyway, since two adjacent cylinders are low it's pointing to a head gasket breach and the gasket breach is located between the two offending cylinders: 2 and 3.
Headgaskets, especially in the early stages, do not always overheat when there is a breach. It depends where the breach is located.
Read:http://www.agcoauto.com/content/news/p2_articleid/200
and http://knowhow.napaonline.com/eight-...n-head-gasket/
Headgaskets, especially in the early stages, do not always overheat when there is a breach. It depends where the breach is located.
Read:http://www.agcoauto.com/content/news/p2_articleid/200
and http://knowhow.napaonline.com/eight-...n-head-gasket/
10-31-2017
#14
If you think a good mechanic is expensive, try hiring a bad one
Re: Rough/low idle and a misfire code
cylinder # 2 (the misfiring one) had zero, no compression. cylinder # 3 had only 30 psi,
If it's a head gasket and warped head, that's one thing; but if it's a valve leakage problem that is more than just a head gasket job.
Check/adjust valve clearances then recheck compression.
If no improvement, then continue with leakdown testing to see where that lost compression is going.
