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Running Lean, Idle Probs... *sigh* Need help...


240Z_Master

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RB25DET - Stock ECU

 

Okay, I can't seem to figure out what is wrong with my car...

 

Fuel Pressure - Good 37 PSI, 40 PSI with motor off

Vacuum - Good, No Leaks

Water Temp - 81.C

Timing - Dead on, 15 Degrees Base Timing

O2 Sensor - Jumps around like it's supposed to when it warms up

Spark Plugs - Good, What's the proper gap?

MAF Voltage - Good

ECU - No Fault Codes

TPS - Right on

 

Idle - 1100-1200, Can't get that sucker to come down, with the screw all the way in that's the lowest I can get it, with it out it jumps between 1200-1300.

 

A/F - The ECU seems to think it runs lean, so it auto corrects to run rich, and then it just seems like the signal is too slow, so it thinks it's too rich and readjusts to lean and dances back and fourth.

 

I checked all this with Nissan DataScan

 

Anything else I can adjust/check? I'm running out of ideas...

 

Going to do a compression test again within the near future to see if there are any leaks in that department valves or rings or what not, but I highly doubt it.

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I had a very simaler problem. Do yourself a favor and take the IAC off of the manifold and clean it. Mine was so carboned up it was seized.

 

Next, check the secondary valve thats under the intake manifold. It has a 1/2" hose running out either side and is supposed to slowly close as the motor warms up. Mine stopped working, so I took it off. Makes the car hard to drive when its cold (likes to die).

 

Make sure you have power to your o2 sensor heater, that was my problem.

 

I had the same symptoms and thats how I fixed it.

 

Evan

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I had a very simaler problem. Do yourself a favor and take the IAC off of the manifold and clean it. Mine was so carboned up it was seized.

 

Next, check the secondary valve thats under the intake manifold. It has a 1/2" hose running out either side and is supposed to slowly close as the motor warms up. Mine stopped working, so I took it off. Makes the car hard to drive when its cold (likes to die).

 

Make sure you have power to your o2 sensor heater, that was my problem.

 

I had the same symptoms and thats how I fixed it.

 

Evan

 

Do I even need the secondary valve? Can I perhaps make a blockoff plate for that and disconnect the 1/2" hose? I think that 1/2" hose is supposed to be redirected into the intake no?

 

Since I have the GReddy plenum, I had to run a hose all the way across the engine bay and plumb it back into the intake after the MAF and before the turbo.

 

This is the air regulator from memory. Does this need to be cleaned? I'm totally confused now that it has been a long time.

DSC05306.jpg

 

 

Which one is this again? Is this the secondary valve you took off?

DSC05311.jpg

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The part in the first picture thats bolted onto the intake manifold is the one I totally removed. Motor will die on decel from high rpms on occasion but not enough to bother me honestly. I may put it back in, but you can definitely remove it for testing purposes. You will have to block the hoses off.

 

The ACC or IAC, I don't remember what the FSM calls it, is whats in your hand in photo two. The plunger/springs contraption should move freely. You can unscrew the solenoid part from it and blast all the carbon out with brake kleen. Took me a bit to get mine working so it moved freely.

 

Evan

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