98 3.8L IMRC Advice

Hello everyone,

I have read through a lot of information on this topic, I just want to be sure I'm clear on some things before I go any further.

First off, my CEL came on earlier today and I got it scanned. The result was a P1538: IMR stuck open (bank 2), and a P1512: IMR stuck closed (bank 1). From what I can tell, they both always remain in the open position, with neither of them resting on the set screws.

I've conducted several tests based on what I've read here. So far I've done the following:
1. Watched for movement of the IMRCs on start up and shut down, there was none.
2. Connected tubing to the vacuum ports on both IMRCs with engine turned off and did the "suck test". The rear IMRC (closest to the firewall) moved with no problem, with no leakage. There was obvious leakage in the front one, and I could not get it to move.
3. I disconnected the vacuum line from the front IMRC and covered the end with my finger, and the rear IMRC moved into the closed position. When I tried this test the other way around, the front IMRC just set there.
4. I also moved the rods manually. The rear one always moved smoothly, but I noticed the front one binding at times, especially while the engine was running, or right after turning it off.

My conclusion would be that the front IMRC is bad. If I'm off in my thinking, will someone let me know? I was also wondering if it is correct that the plenum has to come off in order to replace this? I read that it was, but could not see exactly why that would be necessary from what I viewed under the hood. However, I was in a bit of a rush, and didn't really have a chance to look everything over really close.

I've seen several recommendations as far as where to get a replacement. However, if anyone has come across any additional places that might have a good deal on one of these, any info would be much appreciated!

You're in luck. I encountered this exact problem with my 98 3.8L recently and your troubleshooting is identical to mine. I replaced the front bank IMRC yesterday and my IMRC codes are all gone now.

To replace it, the alternator has to come off to get to any of the fasteners on the IMRC. Undo the battery cable, pull the drive belt off the alternator, unbolt the alternator and remove. The plenum does not have to come off.

Be VERY careful when removing the actuator rod from the linkage. There is a small plastic fastener that keep it from moving around when activated. It is brittle and easy to break when removing (I did).

You mentioned the rod seems like they are binding. When you have the actuator off, you should try moving the linkage to make sure the binding is not the butterflies inside the engine. If they still feel rough, the butterflies may need to be cleaned. The plenum and upper intake WILL need to come off for that.

I got my replacement from a boneyard, because $200 for a vacuum actuator is absolutely ridiculous. If you do the suck test or cover test on a boneyard IMRC and it passes, you can be pretty confident it will be good. I paid $15 for mine, so I can buy 10 more for the price of a dealer part if this one dies again. If you're not a junkyard fan, you can try rockauto.com for a reman/new part. :)