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Rough Running after IMS Install - Thoughts?

1902 Views 4 Replies 2 Participants Last post by  robcarync
I finally got around to installing my intake manifold spacer that has been in my toolbox for 2 years. Decided I may as well since I had leaking coolant hoses to take care of.

I bypassed the coolant to the upper intake and throttle body. I disabled the thermo sensor thing on the throttle body.

While I was in there, I replaced those 3 spark plugs and wires (other three happening once I figure out the rest of this).

The truck seems to drive OK when the throttle is on, but definitely at idling, it seems to run rough and spit and sputter, which is the opposite of the reported high idle when bypassing the coolant to the throttle body.

My best guesses are

1) Air leak at the spacer (replaced throttle body gasket with a new one)

2) Something with the spark plugs/wires causing a miss (but would this trigger a code?)

3) Additional adjustment I am missing on the throttle body or idle air control valve? Where is the adjuster screw?

I have no CEL codes.
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Good idea. I'm pretty sure I did. All hoses were accounted for I think but I'll double check. Other ideas?

Sent from my VS985 4G using Tapatalk here is the run down:

Truck runs fine before hand.

I remove upper intake plenum. I bypass the coolant lines in the back of the engine. I install 3 new spark plugs and 3 new wires. I install the plastic intake manifold spacer with silicone sealant on both sides. I re-install the manifold, EGR, hoses, etc. I remove the thermo wax pellet solenoid fast idle cam on the bottom of the throttle body with no further adjustments.

Truck runs fine when I am on the gas. But bounces all over the place. It is low, and would cause the engine to die at times when it gets to 400 RPM and lower.

I re-install the fast idle cam thermo element on the throttle body and it makes no change. I triple check all of the hoses are installed properly. They are, minus the coolant ones I bypassed. I remove all of the manifold spacer bolts and install a washer under them to make sure they are getting proper clamping force on the intake manifold spacer. They are. Still runs like crap at idle.

I remove the intake manifold spacer bolts. I separate the plenum and slide the spacer out. The silicone adhesive was stuck to the plenum, but it completely slid/peeled off the plastic spacer with no effort at all. I slide the original gasket back in and clamp the joint tight with the original bolts. I leave the sealant stuck to the manifold runners because I am more concerned with the silicone being ingested in the intake.

Truck idles smooth, though the idle is a little lower around 600-700 RPM at times...but very stable and never dies. I attribute the lower RPM due to the fact that I removed the fast solenoid cam and all of the adjuster screws on the throttle body. I probably need to go back through that and consult the FSM on proper adjustment of the screws.

What I do find interesting is that I still have the fast idle cam assembly on my throttle body, but I also still have the coolant bypassed to the throttle body. Other reports have had wildly high idles at 1000 RPM and up. Not the case with me, though.

I will keep the coolant hoses bypassed for now for no other reason than to make service easier when removing the manifold. I did re-install all the extra coolant hoses with clamps to the throttle body and manifold plenum...just so that if I decide to re-connect the coolant, all I need to do is take my bypass hose at the back of the engine, cut it, and connect the cut ends of the hoses to the respective port on the manifold plenum.

I love mods as much as the next fellow...but sometimes it is best to just trust the engineers that put much more thought and design into the system as opposed to wedging a plastic gasket.

As a side note, with the intake manifold spacer installed, the guide pines for the spark plug wires are no longer functional. Meaning, the little pin on the top of the intake that the rubber boot clips onto to support the wire. If you put the pin through the rubber, the end of your spark plug wire is too short by the thickness of the spacer. Not too big of a deal, but something I didn't think about until I got to it.
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in case anyone runs into similar problems...

i reinstalled the spacer with two factory gaskets instead of the sealant. It still leaked. It looked like to me the bolts were a tad too long to get a good clamp load. I got shorter bolts and used a better wrench to make sure I got the bolts nice and tight. No problems after that.

The extra resistance of the EGR tube made it a little tough tighten the bolts the first time...but I snugged it up an extra half turn or so and it took care of the issues.
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