RB25DET Idling Terribly

[Eric0]

Hello! 
 

I used to drive my RB for about a year without issues  but i accidentally dropped a jack on my pulley pretty hard sooo a rebuilt had to occur. Today I finished her up, threw it back in the car, did all the wiring, and plumbing. I verified for any type of leaks (air included) and it all checks out. I primed the engine until it read about 12PSI oil and started her up. The car started immediately but dropped RPM quickly and began to idle at around 300-500RPM. 
 

Fuel pressure 42PSI

Oil pressure 21-25

coilpacks are 6 months old 
 

I also bought:

•New wideband sensor 

•New O2 sensor 

•New Spark plugs (gapped are .02 like tuner suggested a year ago) 

 

What else could be causing this issue? Could it be the camshaft positioning sensor?

[trel]

.2 gap? Da f**k. Something vacuum related is not hooked up right. Double check, then triple check.

Edited August 9, 2020 by trel

[Eric0]

2 minutes ago, trel said:

.2 gap? Da f**k. Something vacuum related is not hooked up right. Double check, then triple check.

Yeeeeah, I had to run that gap through my tuner twice because it is essentially nothing. Lol. But the car was making 450hp no issues. I’ll double check my vacuums. 

[Ben C34]

4 minutes ago, trel said:

.2 gap? Da f**k. Something vacuum related is not hooked up right. Double check, then triple check.

0.02 inches That would be 20 thou.

0.58mm, no worries

[trel]

Check base timing as well if you're sure vac lines all check out.

[trel]

Just now, Ben C34 said:

0.02 inches That would be 20 thou.

0.58mm, no worries

Ah! Yankee doodle.

[Eric0]

Update #1

I have gone through the vacuum line and they’re all connected and secured. 
 

I ran another air leak test for peace of mind and I noticed like a whistle. The whistle was coming from my atmospheric valve cover vents. Should a significant amount of air be leaving through the vents from pressuring the intercooler system? 

[Eric0]

11 minutes ago, trel said:

Ah! Yankee doodle.

That is funny! I’m thinking I will check base timing, But I did discover a significant amount of air leaving the valve cover atmospheric vents from doing a air leak test, is that normal? 

[Ben C34]

19 minutes ago, Eric0 said:

That is funny! I’m thinking I will check base timing, But I did discover a significant amount of air leaving the valve cover atmospheric vents from doing a air leak test, is that normal? 

No that's not normal

check pcv valve.

[Eric0]

9 minutes ago, Ben C34 said:

No that's not normal

check pcv valve.

I did an RB26 valve cover conversion on my RB25 so I deleted stock PCV. 
 

I would I go about checking? I was thinking my throttle body could be leaking or my idle motor?

[Duncan]

Brand new engine could have a lot of air past the rings and out the cam covers. Not a particularly great breather setup as shown, at a minimum hook them both to a catch can filled with steel wool then vent to atm from there if you want atmo venting.

If you are certain it is not an intake leak after the AFMs, most likely the timing is incorrect or the timing belt is a tooth out. You need to set the timing immediately after startup on a new engine.

I can see you have FFP, how is the idle air controlled? Is there a cold air bypass of the throttle?

BTW, if you had location in your profile it would have been easier to guess you were talking imperial not metric....

[Eric0]

27 minutes ago, Duncan said:

Brand new engine could have a lot of air past the rings and out the cam covers. Not a particularly great breather setup as shown, at a minimum hook them both to a catch can filled with steel wool then vent to atm from there if you want atmo venting.

If you are certain it is not an intake leak after the AFMs, most likely the timing is incorrect or the timing belt is a tooth out. You need to set the timing immediately after startup on a new engine.

I can see you have FFP, how is the idle air controlled? Is there a cold air bypass of the throttle?

BTW, if you had location in your profile it would have been easier to guess you were talking imperial not metric....

Hello Duncan,

I was planning on running a catch can after the car was assembled. 

I currently run my engine on a stand-alone ECU (Link) so I don’t have an AFM. I have checked vacuum lines on the intake manifold and nothing leaks. The only air escaping I can hear is from my valve cover filters.

I’m unsure what an FFP is but I have attached a picture of my throttle body. It does have an idle bolt that can be manually adjusted.

I will verify timing, however, this is a step I haven’t done in awhile, could you perhaps write a procedure? I can always look online as well. 
 

I’ve never had issues with my RB so this is a new thing for me, I apologize if I seem a little challenged. 

[Ben C34]

So what exactly has changed since it was running nicely 

[robbo_rb180]

Ffp = forward facing plenum. 

Have you adjusted the screw on the idle air control valve under the plenum or is the link controlling idle by ignition timing? 

If low idle and no leaks, its not getting enough air. Also plug in the inlet air temp sensor as it may have an idle control table that may use it. 

[GTSBoy]

An FFP is akin to an FFS!

[Eric0]

3 hours ago, Ben C34 said:

So what exactly has changed since it was running nicely 

Nothing changed. Other than the new spark plugs and o2 sensor. I did misguide the engine as I was putting it in the car and accidentally bent the cruise-control butterfly on the throttle body. But I just bent it back to straight. I don’t actually use that butterfly so I didn’t matter to me. Could have caused the throttle body to adjust wrong?

[Eric0]

2 hours ago, robbo_rb180 said:

Ffp = forward facing plenum. 

Have you adjusted the screw on the idle air control valve under the plenum or is the link controlling idle by ignition timing? 

If low idle and no leaks, its not getting enough air. Also plug in the inlet air temp sensor as it may have an idle control table that may use it. 

I have not, Im also unsure how to do that. Would you mind letting me know how? I’m getting a lot of air through the valve cover filters. The inlet temp sensor I have never used. I don’t even have a plug for it

[Eric0]

Just to check this off with you guys, I unplugged the connectors on my idle air control and just inspected the connections and the purple connector circled can be turned 360 degrees on mine. Does that mean it’s broken or is it fine?

Edited August 9, 2020 by Eric0
Complete write

[robbo_rb180]

Adjust this screw, the iacv is under the plenum will need a short screwdriver 

[Eric0]

30 minutes ago, robbo_rb180 said:

Adjust this screw, the iacv is under the plenum will need a short screwdriver 

Awesome! That seems simple. Should I turn left or right? Also, does your purple connector rotate 360 degrees?