Rough idle
11-29-2011, 11:26 AM
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Rough idle My 97 ss occasionally runs rough at idle (1k rpms). It doesn't always do it, though. At WOT, it seems to run normal. When I try to take off in first, it's like it's missing or not running on all cylinders. It makes it very hard to take off in first without stalling. Also, at low RPMs in 5th and 6th gear, it doesn't feel like it's running right. My SES light is not on, but earlier I threw a HO2S Bank 2 Sensor 2 code. Would downstream O2 sensors effect performance like this? If not, what could the culprit be?
Thanks,
Spence
Thanks,
Spence
12-01-2011, 12:23 PM
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Ok well, I replaced my EGR valve with another one I had laying around. Same problem. It runs really rough when sitting still and idling during the daytime (fairly warm, about 60-70 degrees out), but when night time comes and it's freezing (40 degrees or so), when I start my car cold, as I take off it stalls until it gets a little warmer. The engine also takes a while to warm up now. Also, popping from exhaust when revving at idle (did this before I had problems, not sure if relevant). Smells like it is running rich as well.
O2 or EGR system or what?
O2 or EGR system or what?
12-01-2011, 12:43 PM
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Motor taking awhile to warm up could just mean a 160 T Stat , Sounds like MAYBE Opti I'm not one to jump on the "Opti" bandwagon but it sounds possible here in your case
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12-01-2011, 12:52 PM
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I have a normal thermostat and MSD optispark (replaced recently), along with MSD wires and NGK plugs. I will try changing out the coil here shortly and see if that fixes anything.
12-02-2011, 11:49 AM
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Well, I replaced the coil. The problem is still present. It runs rough and vibrates at low rpms (generally anything under 1500, and above 1000).
Also, code P1657 (skip shift solenoid) keeps popping up every now and then. I don't know if this is related at all. I replaced the fuse to be on the safe side. I also have a skip shift eliminator (resistor put in the plug).
Also, code P1657 (skip shift solenoid) keeps popping up every now and then. I don't know if this is related at all. I replaced the fuse to be on the safe side. I also have a skip shift eliminator (resistor put in the plug).
12-02-2011, 03:56 PM
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Did the misfire exist prior to installing the MSD Optispark / wires and NGK plugs? If you worked on something recently, that's usually the first place to start looking.
For a misfire @ low RPM, I'd lean more towards an ignition-related problem. Electrical energy always follows the path of least impedance, and under load, that path might not include the cylinder. However, throwing money at the problem isn't really the best way to troubleshoot. Do as much "free" testing as you can before buying new parts.
Few random ideas:
To be clear, a misfire can smell rich to your nose, but the car's computer will perceive it as a lean running condition. Oxygen sensors cannot detect fuel -- they only detect oxygen -- and the excess oxygen from a misfiring combustion cycle will be picked up by the oxygen sensor. As such, the computer subsequently adds fuel to compensate for a "false" lean condition, making it smell even more like fuel (because there is, indeed, more fuel).
Situations like this are why I like having a Scanmaster mounted on my dash -- you can instantly check all of the sensors, determine engine vacuum, and at least narrow a misfire down to one bank of the engine by looking at the block learns. A misfire will create a perceived lean condition, so the PCM will add fuel to that bank (BLMs above 128). If it's a random misfire (affecting all cylinders), then I'd suspect things like the ignition coil / ignition control module / optispark / dirty MAF / bad upstream oxygen sensor / bad fuel pressure -- anything that would affect multiple cylinders, which can all be tested cheaply or for free.
Hope you get it figured out.
For a misfire @ low RPM, I'd lean more towards an ignition-related problem. Electrical energy always follows the path of least impedance, and under load, that path might not include the cylinder. However, throwing money at the problem isn't really the best way to troubleshoot. Do as much "free" testing as you can before buying new parts.
Few random ideas:
(1) Go out at night, pop the hood, and check for blue arcs of light around the ignition wires with the engine running.
(2) With the car off, check for loose spark plug wire connections, and/or loose spark plugs. Take the wires off one at a time (both at the opti and at the cylinder) and make sure they click back into place -- sometimes the MSD wires give me trouble that way. One of the spark plugs may be cracked, or if using the kind of plug with a screw-on terminal, sometimes those terminals can back off and make a loose electrical connection.
(3) Disconnect the optispark's electrical harness and check the connector contacts to make sure the pins are not damaged.
(4) Perhaps pull one fuel injector electrical connector at a time with the engine running to see if one of them doesn't affect the rough idle condition, which would help narrow down which cylinder is having trouble. You could do this with the ignition wires, but you run the risk of shocking yourself with the car running.
(5) Alternatively, it could be something like a vacuum leak -- leaks can cause a rough idle (as well as a lean running condition due to unmetered air entering the cylinders, which can lead to misfires) -- albeit a bad leak would likely throw a DTC for a lean running condition once the BLMs max out.
(2) With the car off, check for loose spark plug wire connections, and/or loose spark plugs. Take the wires off one at a time (both at the opti and at the cylinder) and make sure they click back into place -- sometimes the MSD wires give me trouble that way. One of the spark plugs may be cracked, or if using the kind of plug with a screw-on terminal, sometimes those terminals can back off and make a loose electrical connection.
(3) Disconnect the optispark's electrical harness and check the connector contacts to make sure the pins are not damaged.
(4) Perhaps pull one fuel injector electrical connector at a time with the engine running to see if one of them doesn't affect the rough idle condition, which would help narrow down which cylinder is having trouble. You could do this with the ignition wires, but you run the risk of shocking yourself with the car running.
(5) Alternatively, it could be something like a vacuum leak -- leaks can cause a rough idle (as well as a lean running condition due to unmetered air entering the cylinders, which can lead to misfires) -- albeit a bad leak would likely throw a DTC for a lean running condition once the BLMs max out.
To be clear, a misfire can smell rich to your nose, but the car's computer will perceive it as a lean running condition. Oxygen sensors cannot detect fuel -- they only detect oxygen -- and the excess oxygen from a misfiring combustion cycle will be picked up by the oxygen sensor. As such, the computer subsequently adds fuel to compensate for a "false" lean condition, making it smell even more like fuel (because there is, indeed, more fuel).
Situations like this are why I like having a Scanmaster mounted on my dash -- you can instantly check all of the sensors, determine engine vacuum, and at least narrow a misfire down to one bank of the engine by looking at the block learns. A misfire will create a perceived lean condition, so the PCM will add fuel to that bank (BLMs above 128). If it's a random misfire (affecting all cylinders), then I'd suspect things like the ignition coil / ignition control module / optispark / dirty MAF / bad upstream oxygen sensor / bad fuel pressure -- anything that would affect multiple cylinders, which can all be tested cheaply or for free.
Hope you get it figured out.
Last edited by Alex94TAGT; 12-02-2011 at 04:04 PM.
12-04-2011, 09:51 AM
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Thanks a lot Alex, that was extremely helpful. I popped my hood at night and saw the arching on the 8th cylinder plug wire. Looks like I'll be replacing that tomorrow.
Again, thanks a lot.
Again, thanks a lot.
