Intake manifold leak - how common are they?

I have no idea what they did. I'm going to go over there today to talk in person. The problem with most shops is they seem very sure of themselves and don't like taking suggestions. My last few guesses is the throttle seal, vacuum hose popped off, or silicone on the charge pipe to turbo.

I'm going to try your vac leak test method at the shop I use to work at and figure this thing out myself. The main thing I brought it to them for was an oil leak which they found off the valve cover gasket and valve train noise which they did agree was loud and are going to see whats going on.

Whats so stupid though is I was having this starting issue where there car would start and die off immediately unless my foot was on the gas. Vacuum leak problem huh.... Well it's rare and hasn't happened for the shop yet and I know never will. I guess it's up to me to find this shit lol.

Can the engine run rich from a leaky manifold gasket or just the manifold itself a little loose?

Wouldn't a loose manifold cause a leak? So I will say an ambiguous "yes."

Being the Z31 is a MAF car, it'd be more likely to be lean from a vacuum leak, not rich.

Are you sure you don't have an exhaust leak? An exhaust leak prior to the O2 can cause a hissing sound and cause the o2 to think the car is lean, and thus enrichen the mixture.

[quote]michaelp wrote: I though exhaust would sound more … mean than a hiss haha

[quote]michaelp wrote: I though exhaust would sound more … mean than a hiss haha

Well here are my conclusions after countless amounts of testing.

A) I have no exhaust leak
B) I have no vacuum leak
C) I have no coolant leak
D) I have no boost leak
E) My compression was changed from 7.8:1 to 9:1 in the rebuild process and was told by a guy from finishlineperformance (big domestic racing shop) that it might be rich because it takes in less air with higher CR and ECU sends it the same amount of fuel (I think our ECU's would compensate, but I could be wrong)
F) Main conclusion: I need Nistune to tune it.

G) Possible alternatives:
O2 sensor
Bad MAF
Possible unnoticeable silicone coupler leak

Other than this I'm stumped till I tune it.

[quote]maverickxeo wrote: [quote=michaelp]Small exhaust leaks can cause a hissing noise.

Even at ONLY partial throttle? (not idle or WOT)

Just thought I would revive this. I was out on a cruise night with some people and happened to see a z31. My car had it's rare starting problem where it's really lean and will die right away (sputtering sound). He told me he had the same problem and to replace the cap and rotor. I think this might fix my rich conditions as well. I could be having spark issues where it's not firing and is drowning the cylinders.

monitor the cap while at night with the hood up and no lights around. see if you can see sparks arching through the cap. the cheap recycled plastic ones that look marbleized compared to the shiney black or brown ones from Beck/Arnley or Nissan tend to arch right through the shitty plastic.

Mine was an OEM Nissan part. I just ordered another cap and rotor today though. My cap contact points were a little bit messed up and I'm going to install the rotor myself this time so it will be done right.

So I found a few leaks:

Coupler to throttle body was bad; replaced that and put on t bolt clamps. A few hoses underneath throttle body were off too. Fixed those, and still had a boost leak. After thinking about it for a while; I checked my boost gauge and noticed a lot of air coming from the hose. I was wondering why I could only hear it with the windows up… :nanan?re

I did a smoke test like you guys recommended and wow does that fix your problem fast. I fixed like 5 leaks in a matter of seconds of the smoke coming out. Also popped the cap and rotor on a few days ago and have had no problem since. She idles a lot better as well (except for stupid ebay bov still sucking)