Cold idle miss??
12-09-2018, 07:52 PM
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Cold idle miss??
Long time reader first time poster. Thanks for a very informative forum!
Little background: long time auto enthusiast and 16 years in the auto industry, however new to Porsche. Purchased a 1999 996 C2 Tip with 89k about three months ago. Purchased the car knowing it needed a little TLC, but all in all looks, drives, and runs good.
The issue: when the car sits overnight (in garage, not heated, issue surfaced when weather changed) and I start it. Initially it starts and idles smooth as butter. 2 minutes into idleing I start to get an intermittent poof sound (misfire?) from bank 2. Other bank is still smooth as can be. No codes whatsoever. It does this for about 5 minutes then runs smooth again and continues to run smooth with no issues once it is warm. When the car misfires the dash and interior lights dim as well.
Items I have checked: I replaced plugs, coils, spark plug tubes, fuel filter, cleaned MAF, TB, IAC and changed oil and filter (no metal in filter) when I purchased it. Have gone back and re swapped coils and plugs on bank 2, no change. Vacuum test at almost 5in on manometer. Secondary air pump seems to work correctly.
I find it odd that it is isolated to one bank and that it does not display symptoms at initial start up. Nor once it is warm.
i will try to get a video tomorrow.
Any ideas?
Little background: long time auto enthusiast and 16 years in the auto industry, however new to Porsche. Purchased a 1999 996 C2 Tip with 89k about three months ago. Purchased the car knowing it needed a little TLC, but all in all looks, drives, and runs good.
The issue: when the car sits overnight (in garage, not heated, issue surfaced when weather changed) and I start it. Initially it starts and idles smooth as butter. 2 minutes into idleing I start to get an intermittent poof sound (misfire?) from bank 2. Other bank is still smooth as can be. No codes whatsoever. It does this for about 5 minutes then runs smooth again and continues to run smooth with no issues once it is warm. When the car misfires the dash and interior lights dim as well.
Items I have checked: I replaced plugs, coils, spark plug tubes, fuel filter, cleaned MAF, TB, IAC and changed oil and filter (no metal in filter) when I purchased it. Have gone back and re swapped coils and plugs on bank 2, no change. Vacuum test at almost 5in on manometer. Secondary air pump seems to work correctly.
I find it odd that it is isolated to one bank and that it does not display symptoms at initial start up. Nor once it is warm.
i will try to get a video tomorrow.
Any ideas?
Last edited by Chern996; 12-10-2018 at 04:23 PM.
12-09-2018, 10:53 PM
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No, idle does not hunt. RPMs stay steady. Oil pressure does not fluctuate nor does the charging system voltage. This one really has me stumped.
The sound is like a quick “poof” out of one side of exhaust ( bank 2) and when it happens interior lights dim. No mechanical noise from the engine, smoke, or excess fuel smell. You can feel it through the car when inside. Rev it up while it is happening and it revs smooth, no hesitation.
I have a scan tool, and any “old school” test tool you can think of but looks like I’ll be ordering a Durametric sooner than later.
The sound is like a quick “poof” out of one side of exhaust ( bank 2) and when it happens interior lights dim. No mechanical noise from the engine, smoke, or excess fuel smell. You can feel it through the car when inside. Rev it up while it is happening and it revs smooth, no hesitation.
I have a scan tool, and any “old school” test tool you can think of but looks like I’ll be ordering a Durametric sooner than later.
Last edited by Chern996; 12-10-2018 at 04:24 PM.
12-10-2018, 03:13 PM
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The first video shows a cold start. Car was stored overnight in the garage. Outside air temp shows 49 degrees Fahrenheit on the dash, temperature outside (garage door open is 39 deg). I attempted to show the oil pressure and voltage gauges at start up, but video quality didn't come out that great. Car runs smooth, I believe video makes the engine sound louder than it is.
Second video starts after the car has run for about 4.5 minutes. You hear a "tah" sound coming from bank 2.
Again let it idle for about another 5 minutes, until warm, and it runs smooth for the rest of the day.
Second video starts after the car has run for about 4.5 minutes. You hear a "tah" sound coming from bank 2.
Again let it idle for about another 5 minutes, until warm, and it runs smooth for the rest of the day.
Last edited by Chern996; 12-10-2018 at 04:26 PM.
12-10-2018, 04:22 PM
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It doesn't sound like idle to me, what's the tach/rpm at? Second video says "unavailable"...
12-10-2018, 04:41 PM
#7
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It sounds like a misfire. Also according to your tach, it's at around 8-900 rpm which is a little high, but not as high as it sounds in the first recording... The nice part is, there's no ticking/tapping/slapping etc... The lights dimming could just be from the little hiccup (alternator slows for a split second). Also seems like there's quite a bit of water-vapor coming out of the exhaust (enough to form those drips in the tailpipe) - could just be from the cold start, but you could also have an abundance of condensation in the crankcase. Do you do a lot of short trips? When was the last time you changed the oil?
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12-10-2018, 04:50 PM
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I do get a lot of water out of each tail pipe. It is very humid here right now though. Most of the time when I drive I see at least 30 miles. Oil was changed 1,000 miles ago and I check it regularly. Never noticed any sign of moisture (milky, watery, etc) in the oil.
It is just odd that it only does it after idling a few minutes, on one side, and goes away after warm.
It is just odd that it only does it after idling a few minutes, on one side, and goes away after warm.
12-10-2018, 04:54 PM
#9
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There are several well regarded Porsche shops around Atlanta - I'd let them listen to it and see what they think. Also, maybe a video with the rear lid open - it's possible that it's coming from one of the belt driven accessories.
12-10-2018, 06:50 PM
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Yes there are some VERY good shops nearby, but I love a challenge so that will probably be last resort. I will try a get a video with the lid up tomorrow. I did install a water pump, thermostat, and new belt shortly after getting the vehicle due to a small leak behind the water pump pulley. When I had the belt off I inspected all of the pulleys for play and worn bearings and found nothing out of the ordinary.