Irregular Idle! Please Help

[Allaboutthesnail3]

If anyone could help that'd be great.. I have a CEL code P2178.. which means lean at idle.. The car has new fuel pump internals, I have AP to check the fuel pressure and it's good. The purge valve is brand new.. MAF is new.. I checked the engine vacuum by disconnecting one of the hoses that goes to intake manifold, checking the vacuum pressure there and it fluctuates very rapidly between 21 and 19 inches of mercury..

[Djohns]

Did you do a boost leak test yet?

[MSMS3]

Sounds to me like you have a vacuum line leak somewhere, maybe a cracked or split hose.

[Allaboutthesnail3]

Yeah I think your right about a vacuum leak somewhere... Let me correct my problem, I think it was late and I was sleep deprived, but I don't have an irregular idle, its actually pretty steady.. What I have is a non steady vacuum pressure from the intake manifold.. I did a smoke test and didn't see any leaks.. I can't hear any leaks, I checked the exhaust when I did the smoke test didn't see anything.. car runs good it's just that little leak somewhere that is throwing the CEL and annoying the crap out of me.. I tried spraying all the hoses with carb cleaner and idle never went up.

[Allaboutthesnail3]

One thing I hate is when people resolve their car issues and never bother to post up their solutions... So I'll recap I had code P2187 Lean at idle. After trying a ton of things including buying a new MAF (wasted money and can't return it).. I actually thought I had messed up valve stems and was thinking about paying 1500 to do that job Turns out it was a leak but not an intake leak it was actually a leak where the exhaust meets the engine.. I crawled underneath the car and saw oil underneath one of the bolts on the header (behind engine right next to turbo) and didn't worry too much about it, but then after trying everything I thought it would be worth a shot to tighten up the bolts and once I did the CEL disappeared

[MSMS3]

Thank you for reporting the solution. That makes this thread valuable to others. Hat is off to you, sir!

[Allaboutthesnail3]

Now while the CEL is gone, I checked the vacuum at manifold with my handheld vacuum pump (mityvac) and needle is fluctuating between 21.5 and 21 inches of mercury. So it isn't steady and I still hear the engine hiccup and idle a little bit. So perhaps to get rid of all of that and have things perfect I believe I need to change the exhaust manifold gasket, not sure when I will be able to do that but I will update if I do it, perhaps during christmas break.

[meicalnissyen]

Originally Posted by Allaboutthesnail3 Now while the CEL is gone, I checked the vacuum at manifold with my handheld vacuum pump (mityvac) and needle is fluctuating between 21.5 and 21 inches of mercury. So it isn't steady and I still hear the engine hiccup and idle a little bit. So perhaps to get rid of all of that and have things perfect I believe I need to change the exhaust manifold gasket, not sure when I will be able to do that but I will update if I do it, perhaps during christmas break.

This is a fascinating way to get a bad idle.

all hard parts and fueling good

but a interupt in the feedback loop

nuthing is wrong with ANYTHING

except the WB O2 is getting an inaccurate signal.

2nd the posting of an odd, but documentable issue

[Allaboutthesnail3]

Yes it's been a while and I've finally had some time and help to attack the evil exhaust manifold.. wow, atleast in my experience was incredibly difficult. It's honestly not as hard as removing intake manifold (which i've done) but reaching certain bolts is fucking ridiculous.. I guess that's why people charge $600 for doing that job..well updating this post on that P2178 code, tightening the bolts helped but I could tell that was just a band aid, so I changed out the gasket.. Haven't had the time chance to drive the car yet but I will update on how it feels now with new exhaust manifold gasket in place...

[Allaboutthesnail3]

Car still throwing the lean code, so the problem wasn't the exhaust manifold gasket.. I am going to go at this problem by looking at the ignition coils, because I checked my engine vacuum with my mityvac at the intake manifold.. and it slightly fluctuates at 21 inches.. So looked that up and it is believed to be an ignition problem when you get that kind of read... So I checked my ignition coils today and my first coil is different compared to the rest.. the read from terminal 1 and 3 should be .200 or so ohms (the number doesn't really matter I think) and the numbers should be going down, the numbers in my first ignition coil are going up instead of down so I'm going to replace that coil and see what happens...

[sheston]

Does it run fairly well? If so, post a WOT log, that might tell us enough to help more. I'm not sure what you mean by smoke test? Is it basically a leak checker that you put smoke in with? If you just have it pull in smoke, you'll miss the leaks we're talking about.

[Allaboutthesnail3]

I've never really datalogged with my AP, How do you do that? I've only ever looked at live data.

[tehron]

Op, do you have an aftermarket intake? Are you running a tune with that AP or just logging for now

[Allaboutthesnail3]

No aftermarket parts, only mod on the car is an occ, and HPFP internals. No tune I'm using the stock map.

[sheston]

Search for how to do a WOT log on here. You set the parameters you want to record in the AP. Then you warm up the car, look at live data on the AP, when you push the button is will start logging and push it again it will stop. Then come home and transfer it to your computer using access port manager.

[Allaboutthesnail3]

Ok so I made this thread for anyone going through anything similar to my experience.. So to recap I was throwing the CEL for about 4 months or so, and I replaced many parts (ignition coils, MAF Sensor, Boost solenoid, exhaust manifold gasket, purge valve solenoid, probably forgetting other parts) I decided that since I have a HPFP internals and on my AP fuel looks good, I ruled out fuel. Vacuum leaks did worry me but I checked all my hoses and couldn't find a leak after trying many methods to find the leak I decided the problem wasn't unmetered air entering the engine, although having a boost leak test is always a good thing, I didn't do that I was about to but I didn't.. Now the symptoms of my car were lots of popping coming from exhaust (not super loud popping but I could hear it with driver door open) and idle didn't sound very steady or good. vibration coming from engine at idle, and the worst of all my boost was erratic I could not boost it felt like when you lug the engine. I was thinking perhaps a bad O2 sensor, but before spending more money I said let me check my ignition, after testing the ignition coils they were all in the same range; good. So I checked my spark plugs, the first three seemed similar and in pretty good shape (All 4 spark plugs only have about 3k miles on them and NGK Iridium so they aren't shitty spark plugs) The last spark plug was black and as soon as I saw it I knew it was not in the same gap range as the others so I took my tool and checked it and it wasn't it was at like .23mm instead of the .28mm gap it should be at, after that I reset everything by unplugging the battery for a while then fired it up and the car still ran like shit that day, but the day after it was like night and day car runs great, it's been about 4 days or 100 miles and the CEL hasn't come back, hope this helps ppl, and if you have a problem it's just a matter of finding a solution! P.S. I'm not a mechanic, its just a hobby.