Car drives fine then looses vacuum at idle

[mattg1.8]

Been experiencing an intermittent idle issue for a while now. Car has k04's and supporting mods including fuel pump. I'll start it up and it idles fine then I'll drive at least 20 miles and it runs perfect. As soon as I stop driving and come to idle for more than about a minute my vacuum will go from ~19 to ~12 and the car will start to shake. I don't know why it's happening only after I'm driving for a while but it's pretty weird. Any suggestions?

[vavJETTAw36]

Do the revs go up too?


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[mattg1.8]

The rpm drops by about 100

[vavJETTAw36]

How long has it been stage 3? How long has it been acting up?


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[mattg1.8]

How long has it been stage 3? How long has it been acting up?


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I just bought it 2 months ago but it's been stage 3 for about 16k miles. I'm not sure if it was doing it for the previous owner too. It's been acting weird ever since I got it smogged in ca.

[phila_dot]

Misfire

[vavJETTAw36]

any codes?


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[mattg1.8]

I had a check engine for coolant temp sensor and cyl 5 misfire. I cleared the codes and they haven't come back but still having the issue

[Trb1]

I had a check engine for coolant temp sensor and cyl 5 misfire. I cleared the codes and they haven't come back but still having the issue

I'd swap the CTS. Cheap and easy to get at. notorious for causing all sorts of issues with these motors. Seem to plague the 1.8t more often than the 2.7, but a bad CTS can mess with your a/f ratio causing misfires and bad performance/gas milage.

[mattg1.8]

Changed out the cts. So far so good. We'll see how it feels on the longer drive tomorrow. Thanks for the help!

[mattg1.8]

Bringing back the old thread because the problem continues. It usually happens right when I get off the highway then hit stop and go traffic for a bit. I'll come to idle and it'll be 19 then it's like a switch is flipped and it'll drop to almost 10. I start driving again and it's fine. I don't have vag but any suggestions is appreciated

[vavJETTAw36]

What are your fuel trims looking like? Have you checked out your spider hose? I'd check the check valves that are in the vacuum lines.


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[MikeyB3]

is there any chance you could post a movie of the symptom?

[rguil]

Hate to bring it to my car but could the faulty CTS be why my b5 takes FOREVER to warm up?

[mattg1.8]

What are your fuel trims looking like? Have you checked out your spider hose? I'd check the check valves that are in the vacuum lines.


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By fuel trims do you mean from vagcom? I don't have the program and I'm not entirely sure of the fuel setup because I bought it with this current setup. And what's the spider hose?

[mattg1.8]

Hate to bring it to my car but could the faulty CTS be why my b5 takes FOREVER to warm up?

CTS or thermostat

[mattg1.8]

is there any chance you could post a movie of the symptom?

I'll try to catch it when it does it and grab a video.

[mattg1.8]

Not the best video of what's going on but that's it just idling it's jumping around on vacuum

[mattg1.8]

[vavJETTAw36]

I say before you go any further you need to get it scanned and checked for misfires. You'll look at measuring blocks 14,15, and 16 for misfires. If you are getting them, you'll need to fix them. You'll only trip a code if you get over 25 in short period of time. Don't know the timeframe.


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[mattg1.8]

Was able to get it scanned today. This was the result.

[vavJETTAw36]

That looks like an old code. Your cruising trims are actually rich but not even enough to throw a code. Idle is slightly lean but normal.


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