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Diagnostic Trouble Code P1518

new 6/08/2004

Well, I was a bit premature in my first request for help! My friend said he had his codes pulled at AutoZone some time back and they found the P0401 previously mentioned.

I loaned him my el-cheapo code reader ($40 from Harbor Freight) and he pulled the P0401 and the P1518. I told him that, to make sure, he should reset the computer and wait until the codes) came back. He did, and the only one that came back (after a day or so and 5 or 6 run cycles) is the P1518.

So, now I need help figuring out what to do about this code. Oddly enough his IMRC went bad a year or two ago and it was replaced by the dealer. Is there a way to test the IMRC? I read the info at http://www.v8sho.com/SHO/imrc.html and I'm still a bit confused. The voltages posted indicate whether the unit is getting the proper current, right?

Is the only test of the IMRC's operation to visually check and make sure the butterflies open (and more importantly close) on time? The car doesn't feel down on low-end power, so I doubt they're hanging wide open. Without knowing the car better I can't be sure they're not stuck partially open, although there's a definite increase in intake airflow at the 3400rpm mark. He has a K&N cone installed so it's very obvious.

Thanks for any additional help. PFish, if you can post similar diagnosis procedures to what you sent me for the P0401 I'd really appreciate it!

Steve Tatro


P1518                  HU15



I've had this code pop up about 6-7 times since my cam weld last June. I suspect that the butterrfly spindles weren't lubed sufficiently after cleaning, resulting in an occasional hang up. The only times I've gotten the code have been when running hard above 3400rpm for prolonged intervals. In every case, by the time I stopped to inspect the IMRC the butterflies were closed again and seemed to be operating normally so I just cleared the code and went about my business.

I probably won't deal with lubing my butterflies until the next time I pull the intake to clean the secondaries.


1518 indicate the PCM can't tell if the IMRC butterflies are closed after
having been opened, four possibilities:

1. the inner cable has frayed/broken
2. the plastic pulley in the IMRC mtr box is broken
3. the cable end clip is broken IMRC end
4. the IMRC butterflies are carboned open (unlikely)

The IMRC mtr requires the IMRC butterflies return spring to pull the cable
and therefore the motor back to the closed position, thereby allowing the
PCM to determine that the butterflies have closed.

If the cable is frayed then the fix depends on the severity but usually
requires the inner cable be replaced/remanufactured.

The butterflies/shaft themselves are located under the intake runners in the
lower intake (IMRC) manifold.

Unit is not Fud serviceable, no replacement parts, hardware or bicycle shop.

Check for unit operation by following the instruction on the web page,
without removing anything you can see if the actuator arm moves/returns.



Problem is likely to be that his IMRC cable is frayed and is too
long. Start the car. Look at the IMRC linkage (inboard and below the
TB). Grab the throttle linkage and rev it up to the revlimiter (about
3500 in park) I bet you'll see the cable pull them open, got to close
them when you release the throttle, they will close and open right backup.

If you let this go long enough eventually he will have a stuck open code
in the computer but butterflies that are stuck closed because the cable broke.

I'll find the info and send it this evening. Regardless he is gonna need
an IMRC or to repair his existing box. If he wants to buy a new one, the
duratec one will plug in and work.. A little creativity is required to
hold it in place however.

Scott Krietemeyer
Sunbury, OH
99 TG
96 MG



Thanks Scott.

One other thing: will it be painfully obvious where the butterflies might be gummed up? I don't have a V8 at my disposal to look at so if anyone can explain where to look I'd appreciate it.

I'll probably tear into this over the weekend (since the car owner is out of town - with the car).

If I find that the cable has frayed and is causing the butterflies to not close properly, can someone explain the fix? Is it as simple as pulling the excess cable through so that it's taught enough to keep the 'flies closed?

I'm sure some of my confusion will be cleared up when I either tear into the box or see a good picture of the inside of one.

If anyone has a good picture of one feel free to email it to me!

Thanks again,



If the cable has started to fray it will only be a short duration (a week or so maybe) before the cable gives it up entirely, then there will be no butterflies.

If the take wheel is broken his secondaries would be stuck closed and the car seems like a SLO at 5K RPM's....

To see the the butterflies are mechanically sticking open follow the cable back and give it a tug (get a good grip on it with a pair of pliers don't grab on the plastic clip because it would suck if you broke it)... It should open up and if you let go it should snap back with quick speed, just like a throttle plate. If you see them actually stick a bit as they close then they are very gummed up mechanically and that will need to be fixed before you bother replacing or repairing the box.

Rather than unhooking the cable from the actuator, you could unclip the cable jacket from it's bracket and just pull on the cable jacket to open the butterflies, as the cable is still anchored in the box. If the cable is broken this would tell you real quick...

Scott Krietemeyer
99 TG
96 MG

FWIW I jammed a screw driver in my IRM linkage to hold them open at the drag
strip at the ROTB meet last week. No difference in performance that I could

Paul Nimz

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