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Old 04-05-2013, 09:34   #1 (permalink)
jeh
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IMRC not closing at idle

Hi, I have a 98 3.8 Windstar that I rebuilt after an over-heating issue. The problem that I am having is with the IMRC, my understanding is that the IMRC banks should not open unless the RPMS are over 3000 and an increase in TPS. On my engine the IMRC is controlled by vacuum, when the PCM supplies a ground to pin 42 the IMRC solenoid is activated which in turn supplies vacuum to the IMRC actuators which keeps the IMRC banks closed. When the conditions are met with the RPMs and the TPS then the ground at pin 42 goes away which causes the IMRC solenoid to deactivate and the actuators to lose vacuum which opens the IMRC banks. The problem I am having is that at idle, the ground at pin 42 is not activating at the correct times. When you start the van the ground is present which I assume it should be and idle is fine, but as soon as you open the throttle even slightly the ground goes away and the IMRC banks open, this causes the idle to be very erratic and the engine will even stall out. When the engine almost stalls out, RPM drops below about 500 RPM, the ground comes back and the banks close which corrects the poor idle condition, until the throttle is opened again. Well, just to further confuse me I am finding conflicting information in the manual. One section described the IMRC opening over 3000 RPM like I just described and I just found in another section where it says the IMRC opens at 1250-1500 RPM and closes below 750 RPM. I am losing what little hair I have left over this issue. Frankly, at this point I don’t really care if the IMRC banks open at 1250 or 3000, I just need it to close when the engine drops to 750 RPM . I have replaced the TPS, the PCM, checked for vacuum leaks I have checked the incoming voltage and grounds to the PCM, I have cleaned and tested the IAC, and cleaned the MAF sensor. The engine runs great except for the idle when the IMRC banks are open, also I am not getting any codes. I don’t know what else to do, maybe if someone else has my year van they could see at what RPMs their IMRC banks are opening and closing. As a temporary fix I put pin 42 on the PCM to ground which keeps the IMRC banks closed all the time. It idles and drives fine like this but I would like it to operate like it should. Any help would be greatly appreciated.
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Old 04-05-2013, 17:31   #2 (permalink)
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Re: IMRC not closing at idle

Have you checked for vacuum leaks?
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Old 04-05-2013, 18:12   #3 (permalink)
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Re: IMRC not closing at idle

Yes I have checked for vacuum leaks using several different methods, initially I thought that was the problem but I have been unable to find any vacuum leaks. Thanks for the response.
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Old 04-05-2013, 18:37   #4 (permalink)
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Re: IMRC not closing at idle

Do you know what your vacuum is running at?
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Old 04-05-2013, 20:04   #5 (permalink)
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Re: IMRC not closing at idle

No, I don't no how much vacuum it is pulling, I was going to measure it but I couldn't find any information on what it should be.
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Old 04-06-2013, 05:33   #6 (permalink)
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Re: IMRC not closing at idle

I know on the 5.0 it's about 15-16", I assume it should be the same for any engine.
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Old 04-06-2013, 07:40   #7 (permalink)
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Re: IMRC not closing at idle

I will try to get the vacuum reading tonight and get it posted after I get off of work.
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Old 04-06-2013, 16:05   #8 (permalink)
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Re: IMRC not closing at idle

I am reading a little over 18 at idle.
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Old 04-07-2013, 06:40   #9 (permalink)
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Re: IMRC not closing at idle

Ok, did a little digging on figuring out the IMRC system.

HowStuffWorks "How do tuned intake runners work on your car?"
What Is an Intake Manifold Runner Control? | eHow.com

One's a high speed, one's low. Which one is which, not sure, but, since their actions are based on air flow though the intake, try cleaning the MAF to see if the situation improves. Might even try disconnecting it to see if the engine responds different.
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Old 04-07-2013, 10:54   #10 (permalink)
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Re: IMRC not closing at idle

I have already cleaned the MAF sensor and the problem did not change. I have an OBDII reader that gives me real-time readings from various sensors, the MAF being one of them. I am reading around 0.701 lb/min for the MAF sensor at 862 RPM, the reading for the MAF sensor increases as the RPMs and throttle increase and I read around 2.5 lb/min at about 1900 RPM. Not sure what it should be, but the readings are similar but slightly higher than the readings from the 3.0 engine in my ford truck, I’m guessing the higher reading is due to the bigger 3.8 engine in the van but that is just a guess.
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