Celicasaur

Guys I'm stumped.

• I've tried:
• New intake manifold gaskets
• New bolts
• Cleaned both mating surfaces with a scraper
• Followed the torque pattern (10nm + 90* + 10*)
• Removed intake manifold and smoke tested it to find zero leaks
• Brake cleaner sprayed around manifold flanges to find it leaking still
• Yes the little bendy hose thing by the PCV is connected
• Yes also the inner hard black pipe (by the IAT sensor) is securely fastened
• And yes the U-bend pipe that comes out of the manifold is routed correctly under the metal pipe of the engine and not kinked

Supplementary error codes:

• P2270
• P2272

Basically - running lean ^

FWIW I tried to turn the bolts a little more in sequence (probably another 15-20 degrees all over (yes, far from ideal) and it made a marginal improvement to the seal on one or two areas where brake cleaner would make the idle change. Engine temp got high and fan kicked in, which made it harder for me to make sense of how the engine was responding to brake cleaner spray afterwards, so I gave up for the day.

However 1) I'm afraid of turning the bolts any more in case they snap or 2) cross-thread the head.

Any ideas other than getting a friend that smokes to puff through one of the vacuum lines of the manifold and get a clearer picture?

Infiniti

I hope you get this figured out man!

cptncreme

Maybe try cleaning the MAFs with some maf cleaner, dirt can cause in accurate readings

bhamg

I've seen several mentions of warped intake manifolds. This, from a thread here in 2015:

Had the same problem with mine 2 weeks ago. Started my car CEL. Turned it off CEL gone. WOT a couple times and boom instant loss of power and CEL again. Mine was an intake manifold leak. Basically, the inside of my intake had warped. Got the car back and drives smooth and pulls like a freight train. How does the car idle? Mine was idling like ****.

Celicasaur

It's not so much a MAF kinda issue tbh. Idle is high (1000rpm), after a blip of throttle the revs hang and then come down slowly, ignition timing is in the negatives, vacuum is way lower than it should be etc

I really hope it's not warped, but then it shouldn't be either. It was running ok until I removed it recently. I'm guessing/hoping it's a niggle with the reassembly....but then again, I've done this procedure probably around 6 times without any issues. And now upon numerous attempts, I can't get it running happy. Such a PITA.

I've just removed my air boxes and then brought them indoors. I carefully loosened the bolts, re-seated everything and then bolted them back up along with the Y-piece to eliminate any bad assembly in that area. I'll try again tomorrow and see if it makes a difference (air might have been leaking past the MAFs at the back of the air boxes)

deadlyvt

Where is the break cleaner being applied that it causes the engine to ingest it ? Perhaps the gasket or manifold are indeed warped...
On a positive this might mean your larger throttle bodies will work out after all after you fix the leak👍
When I had my intake apart on reassembly one of the manifold bolts was leaking when I took it off noticed one of the bolts had a hairline crack...

Celicasaur

I'm spraying as far down as i can (bearing in mind I'm fighting for space here, what with the air boxes being connected) to the flange area. Part of me wants to remove the bolts and re-torque again, but then again I've done this countless times now (I've got a graveyard of practically new intake manifold bolts) and it's not made a difference.

And yes hehe, hopefully once sorted, this will indeed mean my bigger throttle bodies work out

bhamg

If I were you I'd probably take it down to a machine shop and have them take a look at it, and if the sealing surfaces are not true then perhaps they can address the problem.

BLKROKT

Warped or cracked intake manifold. It seems to be the only explanation left.

Alex.currie44

Not an expert and will never be but recently I posted a couple of links on the engine assembly and from recall they were pretty pointed about sealants being placed accurately on mating surfaces after srupulously cleaning them.
Could this be involved here? Just askin'.

Jasonoff

There's no sealant between the IM and CH, just a gasket.

jptaylor

It's quick and free but I would check the filters in the boxes....remove the entire box, remove and inspect filter seal, CAREFULLY reinstall filters by holding them in the LID and then reinstall boxes...I chased this exact problem and it turned out that the filter seals on both sides were allowing excess air into the system....

deadlyvt

A leak at the air filters is pre maf and won't affect a thing other than unfiltered air and potentially water getting ingested, impossible for it to cause a vacuum leak

jptaylor

Yeah, I'm pretty experienced in how engine vacuum works.....BUT back to my last post, the filters not being seated and allowing air to enter the system from a point outside of the normal airflow path DOES in fact affect idle...my experience tells me that it causes turbulence across the MAF which the computer compensates for by adding fuel, thus increasing idle rpm

skratch77

Op you might have a leak on the plenum that mates to the back of the intake manifold that connects to the air boxes.

A leak there will message with the car big time

skratch77

Also check to see if you have the maf facing the right direction. The little hole needs to be in the path of the airflow coming in and will have one maf look like you installed it upside down compared to the other side

deadlyvt

you could loosen every bolt on the filter housing right off and it wouldn't affect **** if you were just sitting here idling ... goniut and try it ...

jptaylor

Go and try it? I don't have to go and try it I JUST GOT DONE RESOLVING A HIGH IDLE ISSUE BY DOING WHAT I DESCRIBED. I am fully aware that the air in that type of a leak is metered, which is why I referenced the ECU adding fuel to compensate......not that I expect it but how bout YOU go out and place an ink pen cap sideways in the seal rail on the boxes and see what happens to your idle, I promise it is going to rise

....and as far as checking with brake cleaner yes you CAN do it that way BUT it is not only messy but also can lead you in the wrong direction as it will splatter to other areas of the engine giving you a false positive....I have always found the best way to test is with a butane torch/campfire bottle with a hose attached....no mess and because it is a gas already when the idle goes up you KNOW you are in the right location

jptaylor

https://mbworld.org/forums/c63-amg-w204/636437-row-air-box-mod-afe-pro-dry-s-filter-idling-question.html

High idle issue caused strictly by MAF airflow change with ABSOLUTELY ZERO OTHER ISSUE involved.....

Celicasaur

Spent hours and hours over the last few days checking and fettling....doesn't make sense. I'll pop to the machine shop after work today and ask them to check the manifold flanges. If I can't come to a solution by the end of the week, i'll probably just buy a used manifold from ebay and try my luck at one of those. With the amount of times i've been torquing it up, i'm concerned that that threads might get stripped.

I'd double-checked the air-boxes (yeah it can cause a vacuum leak if the seal isn't great via that last screw of the airbox near the Y-pipe) on Friday at home.

Leak at the plenum near the back....you mean by the big oval throat thing? Hmm...it's possible i guess. I've checked the Y-pipe though and can't see any damage. Besides, I've had it on and off so many times now, you'd think that it would seal on one of those attempts by law of averages.

There's a slim outside chance that my injector seals could be an issue (yes, i'm clutching at straws now) so as preventative maintenance also (for the whole sticking injectors and bham, thing) i'm going to send them off for servicing and to get them flow-tested. Who knows, it might pick up a pony or two as well.

skratch77

Double check that y pipe going into the back of the manifold.easy way to check is sparying brake cleaner back there

Celicasaur

I tried man....no dice


However...I think I found the issue today

I bought a mini party smoke fogger thing and went to town on the engine for a couple hours trying to fish out a leak. I was really disappointed and quite sad because there just wasn't anything on the engine side. But then just as I was about to give up and eat some chicken, I thought to fog the intake system (I keep my airboxes and the y-pipe together as one item) - the right side one was air tight...the left side one had a leak behind the maf, which we all know is going to be classed as unmetered air. Makes sense - the screw holes for my airboxes are quite worn out now and they don't clamp down tightly.

So, in true Kye Kelly fashion, I opened the airbox, applied RTV, closed it and clamped it down, then re-tested with the fog machine and couldn't see any more leaks. I've left it to dry and set overnight. Fingers crossed that this solves the problem. I'll update tomorrow hopefully with positive news.

And yes, if this solves the problem, I will of course buy a replacement airbox.

Celicasaur

Damnit, problem still exists

I'm going to take a couple days break from stressing about the car and work on a different one. I'll re-fog the airbox and take it from there.

For reference, the following codes are pending in the ECU after clearing the first batch and then going for a drive:

• Multiple cylinder misfire
• Cylinder 2 misfire detected
• MAP/Barometric pressure circuit range/Performance problem
• 02 sensor signal stuck lean, bank 1 sensor 2
• 02 sensor signal stuck lean, bank 2 sensor 2
• Cylinder 6 misfire detected
• Cylinder 8 misfire detected

Symptoms are the same, albeit slightly better response on the accelerator pedal this time around. The car is drivable, but I'm not too keen on the general running temp that the excessively retarded timing is having on the motor (gets up to temperature inside around 5 minutes of idling and light driving) and also the sound is brutally loud now.

BerBer63

Did you change your O2 sensor? I've gone through 3 with headers?

Celicasaur

I haven't changed them yet, no.

TBH though, the car has the trademark hanging idle which comes with a vacuum leak and also the brake pedal is stiff and weak, ie the brake booster isn't getting the love that it needs either.

I might take a look at it tomorrow if I get time. Not sure what I'm going to find though. The next step might well be to take it to a workshop because I'm out of all rational ideas.