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Discussion Starter · #1 ·
This is my first post since hopping over from the RX8 forums so my apologies if anything is off.

I have an '18 ST1 with a stratified tune, Green Air Filter, Acellatec Catless Downpipe, AWE Catback Track Edition, Mountune Recirc Valve & springs/rims.

This morning I went out to start the car and it started fine and about 10 seconds into idle the RPMS started bouncing up & down (between 1100 - 2000 & then dropped to 600-1200 after some warm up). I let the car run for a few seconds to see if it would work its self out but no luck. I shut the car of and ran in & grabbed my AP to make sure all parameters were fine. My AFR was going from 12-20 which is insane. After poking around on here i thought maybe I needed to clean & re-oil my Green Air Filter & look and see if my MAF needed cleaned out as I had a similar issue on my RX8 after a hard rain here in Florida. I unplugged the MAF but it looked spotless inside, gave it a few courtesy blows to get any possible dirt out & popped it back in. My Air filter looked relativity clean as well so I tried starting back up. The issue seemed to take a few seconds longer to start up again this time but it did indeed continue to happen. I just pulled the air filter and brought it inside to clean & re-oil & Once it dries I will put it back on. I can't imagine however that an air filter that doesn't appear to be alarmingly dirty would cause such a rough idle? Do I maybe need to go into the throttle body? Any help here would be appreciated!
 

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Sounds like a vacuum leak to me, check the seal between your MAF and manifold.
Sprau brake cleaner on the seams while the car is running and if the RPM shoots up you found your leak

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I'll second the possible vacuum leak somewhere.
 

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When looking for vacuum leaks a smoke test is the best way to find them.

You can get a really nice commercially made machine for $125. You can follow Youtube videos to make your own for a fraction of that cost or you can also smoke a cigar and blow the smoke into your intake/EVAP system.

If you’re planning to self maintain 80k+ cars, you should consider acquiring a smoke machine.
 

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FYI, on this car the only place for a vacuum leak is physically on the manifold. Check your sound symposer, PCV tube, throttle body, MAP sensor, and where the purge valve system connects to the manifold.

If the system can’t maintain vacuum in the manifold at idle the engine speed will run away or be unpredictable.

In addition this car doesn’t have a MAF, you cleaned the IAT sensor.
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Discussion Starter · #7 ·
Hey guys sorry for the delay. My dumba** forgot I had an AP. I took it out & was getting the code "unable to bleed up fuel tank vacuum" so i got on and did some research & found its commonly linked to a purge valve. The dealer paid to tow the car in and fix it free of charge. They just text me telling me its replaced but the car is still surging at idle just not as bad. I am going to nurse the car home & check for a vacuum leak as perhaps it was both. Back in December I was having an issue where after I would clutch in the car would tac up on its own & would continue until i let the clutch out. One day it stopped and hasn't come back but I have read that a vacuum leak could potentially cause this?

I will keep you updated.
 

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Discussion Starter · #8 ·
So on the way home from the dealer the car threw an O2 sensor error & i looked it up and it seems to be the upstream O2. Going to swap that out.
 

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2014 ST3. Garrett Powermax turbo, Thermal Turboback, CPE intercooler, JBR intake, Innovative RMM
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Super late but realized I never closed this off. After replacing the O2 sensor the car has ran great!
Thanks for following up!

The "unable to bleed tank pressure" is an indication that your purge valve is failing, and unrelated to an 02 sensor issue. Might want to pop one of those on there before it deforms your tank. Doesn't matter if the recall has been done, the purge itself was never upgraded to solve these issues.
 

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Discussion Starter · #11 ·
Thanks for following up!

The "unable to bleed tank pressure" is an indication that your purge valve is failing, and unrelated to an 02 sensor issue. Might want to pop one of those on there before it deforms your tank. Doesn't matter if the recall has been done, the purge itself was never upgraded to solve these issues.
So interesting to hear that they put the same sh*t purge valve back in.... Are there any aftermarket or "upgraded" purge valves anywhere?
 

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2014 ST3. Garrett Powermax turbo, Thermal Turboback, CPE intercooler, JBR intake, Innovative RMM
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So interesting to hear that they put the same sh*t purge valve back in.... Are there any aftermarket or "upgraded" purge valves anywhere?
An upgrade is in the works by our very own @SSgtjrobertson but for now you can save money by building a FUFF and replacing A 20 dollar valve instead of a 60 dollar valve every time.

 

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Discussion Starter · #13 ·
An upgrade is in the works by our very own @SSgtjrobertson but for now you can save money by building a FUFF and replacing A 20 dollar valve instead of a 60 dollar valve every time.

Thanks for the info! I will read through that thread as mine actually just started throwing the code for the purge valve again....
 
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