FN2 Rough idle when coasting (after cleaning throttle body) - Civinfo
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post #1 of 9 (permalink) Old 10th March 2018, 14:09 Thread Starter
 
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FN2 Rough idle when coasting (after cleaning throttle body)

Idle at a stop seems fine (800rpm, give or take 10), but when coasting to a stop or downhill in neutral (doesn't matter if in gear with clutch disengaged or in neutral) the idle rpms are all over the place. Car runs fine otherwise, no problems accelerating or anything when driving.


Not sure if related, but even when the car is fully warmed up, the RPM at startup jumps to 2k+ and takes about 20 seconds to settle down, is this normal?


Again not sure if related but I like giving data, I found out my PCV valve might be bad, a hissing sound is coming from it, but goes away when the hose is pinched.


Thanks.
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post #2 of 9 (permalink) Old 11th March 2018, 06:40
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vaccum leak.
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post #3 of 9 (permalink) Old 11th March 2018, 13:33 Thread Starter
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Originally Posted by ghost_bhp View Post
vaccum leak.
But that would cause the standing idle to be abnormal also, no? It's only happening when rolling in neutral. My bet is the TPS needs recalibrating, I'm trying to find somebody with an OBD2 bidirectional scanner.

Also noticed that when standing in neutral (around 800 rpm idle so normal) and I rev the car slightly, say 1700 rpm and I immediately let go of the pedal the rpms drop to 1200 then surge back to 1500 and then go back down slowly again. It's really strange. This could be the cause of the massive rev hang I'm getting when shifting gears.
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post #4 of 9 (permalink) Old 11th March 2018, 14:02
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maybe needs the tps reset after cleaning
thats if you cleaned it properly and its not damaged or contaminated any sensors
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post #5 of 9 (permalink) Old 11th March 2018, 14:09
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If you cleaned tb you need to connect it to diagnostic system and do learning procedure
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post #6 of 9 (permalink) Old 11th March 2018, 14:18 Thread Starter
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Originally Posted by scaramanga View Post
maybe needs the tps reset after cleaning
thats if you cleaned it properly and its not damaged or contaminated any sensors
Yes that's what I gathered from googling around.

I probably did not damage anything, didn't even remove the TB, just the plastic air tube, put a brick on the throttle pedal to open it and gently wiped away the black stuff, I don't think I touched anything in there. A faulty PCV valve doesn't give these symptoms right?
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post #7 of 9 (permalink) Old 11th March 2018, 14:21
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Quote:
Originally Posted by Razon View Post
But that would cause the standing idle to be abnormal also, no? It's only happening when rolling in neutral. My bet is the TPS needs recalibrating, I'm trying to find somebody with an OBD2 bidirectional scanner.

Also noticed that when standing in neutral (around 800 rpm idle so normal) and I rev the car slightly, say 1700 rpm and I immediately let go of the pedal the rpms drop to 1200 then surge back to 1500 and then go back down slowly again. It's really strange. This could be the cause of the massive rev hang I'm getting when shifting gears.
I'd still say a vacuum leak, as when it's under load it's probably sealing fine... then once you let off it's closing the throttle plate putting pressure on where the leak is.

Costs nothing to undo everything and ensure all mating surfaces are clean and flush.
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post #8 of 9 (permalink) Old 11th March 2018, 21:17
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Pcv valve needs replacing
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post #9 of 9 (permalink) Old 12th March 2018, 07:13 Thread Starter
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Tested for vacuum leaks, everything is OK.

Resetting the ECM and then doing the relearn solved the idle surging issue. So again, if I just followed the service book after cleaning the TB I would have been fine.

I will replace the PCV valve, too.
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