Swapped injectors, now have surging at idle.

[markseven]

I swapped in new injectors, and now at idle the engine surges to 1500rpm every second or so. Also, the fuel economy needle swings to the left and back like a metronome, and the coolant temp needle blips in time with economy needle.

Only one vacuum line was disconnected, the one that goes from intake manifold to the FPR.

I pulled and reinstalled the fuel pump relay.

The car runs great anywhere above idle...

Any ideas?

TIA!

[mcr_driver]

Are the injectors rebuilt and flow tested? Have you swapped the old injectors back to see if those are the problem or at least eliminate them from the equation?

[not5toes]

Did you disconnect the battery and let the DME reset?

and that vac line is sorta important...

[markseven]

Are the injectors rebuilt and flow tested? Have you swapped the old injectors back to see if those are the problem or at least eliminate them from the equation?

The injectors are rebuilt M50 units (17#), flowed and matched to less than 2% variation. I didn't think it is the injectors since the car runs great off idle, but I may reinstall the original units as you suggested.

Did you disconnect the battery and let the DME reset?

and that vac line is sorta important...

Yep, the battery was disconnected prior to opening the hood, and I double checked the vac line. Maybe it simply needs more time for the DME to wake up?

[markseven]

It's a M20B25, btw.

[Jaxx_]

look for a vac leak where the injectors meet the manifold.

[ParsedOut]

look for a vac leak where the injectors meet the manifold.

This. Or you forgot to hook up/disturbed another vacuum source in the process. Definitely a vacuum leak.

[markseven]

Argh!!! Leak at the mani? Damn. How is that possible? Maybe some debris is pushing against the o-ring?

[K1CKBAC]

I had very similar symptoms and it turned out my engine block to chassis ground cable was bad.

[ForcedFirebird]

The m20 DME will roll idle if there's non-metered air introduced after the AFM. My guess would be an o-ring maybe not seated good?

Also, since you took that bracket off the valve cover to swap them, two of those holes go straight through to the plenum.

[e30kawi]

I had to zip tie the ends of that little vacuum line so it wouldn't leak. Also, get some brake cleaner and spray it around and see if your idle jumps up.

[markseven]

I had very similar symptoms and it turned out my engine block to chassis ground cable was bad.

I had to zip tie the ends of that little vacuum line so it wouldn't leak. Also, get some brake cleaner and spray it around and see if your idle jumps up.

The m20 DME will roll idle if there's non-metered air introduced after the AFM. My guess would be an o-ring maybe not seated good?

Also, since you took that bracket off the valve cover to swap them, two of those holes go straight through to the plenum.

Thank you for the input, guys.

FF, I dropped one of the bolts that holds the fuel rail to the intake manifold and couldn't find it, so I reinstalled with three - do any of those go straight through into the mani?

[K1CKBAC]

If you dropped the bolt while the manifold is still securely fastened then it shouldn't fall into the manifold. It probably got lodged between the head and manifold. I would check if it didn't drop into the head if you had your valve cover off.

[markseven]

If you dropped the bolt while the manifold is still securely fastened then it shouldn't fall into the manifold. It probably got lodged between the head and manifold. I would check if it didn't drop into the head if you had your valve cover off.

It didn't fall into the head, thankfully - it's below the intake, resting on one of those ribs / crevices on the side of the block

[ForcedFirebird]

Those bolt holes do not go into the runners.