So, about a month ago I got my car back together, had the motor rebuilt after having some issues with the crankshaft (had to replace the crankshaft after 2,500 miles on my built motor… replaced all gaskets and rings at the time too)… anyways, the car seems to be running well (only about 100 miles on the car so far…), it just has an unstable idle, the idle surges up and down and the car will usually die.

I swapped throttle bodies with my brother’s 350Z and didn’t notice any change. Then I took the car to Xact dyno and my tuner up the idle via Osiris from 850 RPM to about 1,000 RPM, no change for the better after that (on the drive home I had the same surging idle and when it wasn’t surging it was high, over 1,500 RPM).

My tuner was telling me it’s probably a vacuum leak, while the car was idling he looked at the Osiris log and noticed that while the car was surging the throttle remained closed and car was pulling timing to try to stay at the target idle. I looked everywhere but couldn’t find any leaks… I’m taking it back to Xact dyno to have them try to find any leaks with a smoke machine.

Right now, the car is pulling the following codes: P0031, P0051, P0037, and POO57

It was pulling P0300, P1111, and P1136 too at one point but after disconnecting the ProEFI cam control, I was no longer getting any cam codes.
The other thing I noticed was the car showing it’s running extremely lean at idle (AFR range is 15 – 20) and while driving, under partial throttle it’s displaying an AFR between 10 – 12.

Anyone have any suggestions or experience with anything like this? Thanks!

 

That def sounds like a vacc leak. Smoke machine that sucker. If I had to bet it is something simple like intake manifold gasket or valve cover leak. They can be tricky to find but just trace all the gaskets out then start eliminating line leaks and connection points.

 

Yeah, I think I’m going to pull the spacer out before I take it down for the smoke machine…

I just wanted to make sure I didn’t have any timing issues or anything.

 

first off, did you do a complete TB reset, where the coolant is over 70*C?

You will never get it to idle properly if the TB is not calibrated. I do it every single time i disconnect the battery.

based on you using proefi to tune:

From there, you should be able to look at your MAP sensor to tell if you have a vac leak. I know my car idles at 55kpa. I assume you knew what kpa yours idled at before it was apart.

next, check the idle spark tables. try making the range smaller or bigger. I had mine at +/-15*. Now with a better main timing table, I have it set at +/-8*

if your AFR is not 14.x:1, that will also promote the idle to surge as it causes idle spark to move alot.

make sure that you are not using closed loop at idle either. set it at 1300 rpms or so. I find that closed loop at idle will cause too big of correction swings and can cause surging

good luck

 

Just a quick update, did the smoke test and they didn’t find any vacuum leaks, blow off valve was the only thing leaking.

…and thanks for the detailed response str8dum1! I’ll be going through your recommendations next…

 

Did this ever get fixed?

 

I hope so. This was over 4 years ago.

 

lol I know, but I'm having the same problem and have tried everything... I want to know how he fixed it.

 

Yep, fixed it a long time ago... the issue was with the crankshaft pulley, the shop that built my motor didn't properly secure the crankshaft pulley bolt, after about 2k miles the pulley wobbled enough to wear away at the crankshaft keyway and throw off the engine's timing... I had to pull the engine and replace the crankshaft.