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Title: Help with IMRC Failure DTC

new 11/17/2003

Service Engine light came on and the car didn't have the same high rpm sound I was use to. I pulled the code using the from free diagnostic tool from Murray's. I got the P1518 code. I've scoured through the v8sho.com website and it appears P1518 is a common IMRC (intake manifold runner control) failure (secondary valves in-op).

 My questions:

1) Where do I find the IMRC box under the engine to check whether it's the  plastic wheel inside the IMRC box or a cable failure? The website assembly diagrams appear to place the IMRC box on top of the engine near the battery side. Do I take of the plastic decorative "V8 SHO" engine cover and the IMRC box is right there??

[Christian Andretta] Yes, take the cover off and a silver colored square box with a wiring harness and plastic covered cable will be staring back at you.

2) Is a cable failure obvious?

 [Christian Andretta] Sort of. Have someone sit in the car and give it  gas up to the rev limiter, peek next to the throttle body and you will see a cable move towards the front of the car just before the rev limiter is hit( this shouldn't happen for you because it is not working). Just make sure the cable is connected.

3) Should I disconnect the battery before pulling the IMRC box off the car?

[Christian Andretta] Can't hurt, why not.

4) How should I open up or check the inside of the IMRC box for the broken plastic wheel thing-a-jig?

[Christian Andretta] Four Phillips head screws and break the silicone seal with a flat head.

5) Should I go to the dealer for a new part or check junkyards? 

 [Christian Andretta] I say new.

6) Should I let the dealer fix it for me?  

[Christian Andretta] No way. A couple of things could have happened. Either the wheel broke, cable end snapped off or brake, or secondary are gummed up and will not move. Make sure you diagnose thoroughly to figure out what really happened. Any tips would be appreciated. I'm not an auto mechanic, but I can take apart and put things back with wrenches and sockets.


 John L
Oakland County, MI

To figure out some of what is going on, locate the IMRC linkage (cable that runs just to the left of the Throttle body - kind of buried). You can barely see the cable but with a light you will find it, there are no other cables to confuse it with.

 Start the car (it is important that the car not be driven as I will explain in a second). While watching the cable with the cark in park, open the throttle. You can just pull the throttle cable at the TB, or you could have a helper step on the pedal in the car.

You may or may not see the cable pull. If when it idles back down they will close and then open back up and remain held open even at idle until the key is turned off. This is a definitive sign that you have a cable fraying or gummed up intake. (see #1 and 2 below)

1) Either the butterflies themselves are gummed up and they aren't closing all the way (probably least likely) usually the gummed up intake just puts extra loads on the linkage and causes problem 2 or 3.

2) The cable is frayed and hence longer so the cable end inside the box is not pulled all the way back to the "closed" stop. This is the easiest to repair the assembly without replacing it, but still not a breeze. This is almost certainly your culprit if the butterflies, open, then close and open and remain open in the above test.

3) The cable or plastic wheel inside the control box is broken (this would be the case if the cable didn't pull the butterflies open at all).  Essentially the spring of the intake butterflies themselves have to pull the cable back out of the control box, if this cable is too long (fraying or whatever) the switch inside the box that tells it that the 'flies are back at rest is never set (but they will open the first time the engine calls for them after each start). Also if the cable or wheel breaks there is no linkage to pull the wheel back to rest and set this same switch, so it will also provide the same code.

As many have said the failure of your unit is related to intake deposits at some level. The wife's Cable frayed about 4K after I had cleaned her intake so I just repaired the cable and didn't need to be concerned with intake deposits. You need to make a determination of what you need to do to your car, or if the butterflies actuate smoothly by hand you can always replace the box now, and make it a must do to clean your intake when you get welded in the near future.

I have seen both frayed cables and the broken wheel syndrome. Sounds like others see the broken wheel more than the broken or frayed cable. I have repaired the boxes in both scenarios but if you don't have a few hours to tinker with trying to fix a part you can acquire about $100, I don't recommend it as those control boxes are put together like fort know with sealer. I like challenges and am a glutton...

 Scott Krietemeyer
99 TG
96 MG

Excellent explanation Scott. I would add that by removing the TB and 90 degree intake fitting you can get a very good look at the IRM butterfly linkage.

Here is a picture of the cable end at the linkage.

IRMCactuatorcable2.jpg (39643 bytes)

Paul Nimz

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