Boucing RPM and Idle Surge

[ecbo0m]

Need some help diagnosing a P0171 lean code.

A few weeks ago I got solid CEL and pulled P0171. Cleared it and thought it was fluke given that i put some injector cleaner in the tank and ran the tank to almost empty on separate occasions. Car drove fairly normally until today.

This morning I started to get bouncing idle. Its normally around 800 but now surges up to 1100 and comes back down to 800 pretty consistently. This is ONLY happening at low RPMs i.e. stopped at a stoplight. Otherwise car behaves normally at higher RPMs, though a little sluggish. No misfire the way a CP failure would feel, but notice some exhaust sputter occasionally. When putting the car in park it was surging up to 2.5K RPM.

Otherwise performance is fine and car is still boosting 16+ on stage 1 tune.

Any thoughts? Faulty MAF? The PCV and most check valves have been replaced recently, and i'm not hearing/seeing a significant vacuum leak.

[cmiguel32]

Fuel filter

[imnuts]

I would guess vacuum leak given the lean code and bouncing idle.

[ecbo0m]

Thanks, I think i've narrowed it down to the PRV or PCV valves. Can anyone help me understand how to diagnose/differentiate between the two?

Idle RPMs are bouncing up and down, and engine appears to sputter/misfire sporadically now. I am getting suction on the oil cap, and it stumbles a bit when removed.

There's also some oil seeping onto the PCV valve from the connection under the intake manifold and it feels like oil consumption is greater than before.

[old guy]

Replace the PCV valve. What model year?

Edit: I see you have an '03. If it's a late '03 pick up this kit: Clicky click®



If you have an early '03 pick up this kit: Clicky click®



If you have a late '03 you will have the small vent tube on the back of the valve cover circled in red. If you have an early '03 you will not have that extra breather line.

[ecbo0m]

Thanks OG. Is this doable without removing the intake manifold?

[old guy]

Thanks OG. Is this doable without removing the intake manifold?

It is. I recently replaced mine (late '03) without removing the intake manifold. But be aware it requires working in very tight quarters. I would recommend picking up a new intake manifold gasket (they are very inexpensive) just in case you decide to give up and remove the intake manifold. I know that has happened to several board members.

[ecbo0m]

Thanks again - replaced yesterday. Fixed my rough idle and RPM symptoms and more. With the vac leak the performance had deteriorated over time. Replacing the PCV felt like going stock to Stage 1 again.

A few tips for people doing this in the future:

1. Buy hose clamps and replace all the on-time clamps you can get your hands on.
2. Intake manifold removal isn't necessary. The job took me just over 2 hours, though the working space was tight.
3. Replace all parts, not just whichever piece is visibly broken - both the L breather hose and PCV valve were melted/brittle/destroyed on my car.
4. Remove the N112 and N249 mounting plate under the intake for a little more working room.
5. Remove the L hose, T pipe, and PCV valve together in an assembly. Minimizes the number of hose clamps that need to be wrestled off and gives more leverage for pulling everything out.
6. Ensure that the L breather hose is fully seated with the C retaining clip before tightening the remaining hose clamps.
7. Use a long pry bar from the top of the manifold to get snap the new retaining clip in.

Cheers.

[old guy]

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