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IM already removed? Time to clean the EGR passage

7853 Views 21 Replies 6 Participants Last post by  PaulG
I recently replaced the rear vcg (valve cover gasket) on my car, and in order to do that, the IM (intake manifold) had to be removed. At the same time, I decided to clean the egr passage in the intake manifold. I've never read of anyone on doing it, but I found some writeups and threads on a 626 forum, so I thought I would share. I'm sure some members have done this, but it hasn't been mentioned much.

Once the IM was off, I sprayed tb (throttle body) cleaner in all the intake runners, and did the same for the egr passage. I kept spraying in each runner and tipped the IM so that it ran out of the tb. I stopped when the liquid coming out was pretty clear. I then put the IM back on the car and after a few days started getting the code P0400, EGR Passage blocked. This code got me searching the internet, and I found the 626 forums where this has been mentioned extensively, and they talk about cleaning out the egr passage on the tb side. I had not removed the tb when changing the IM gasket, so I decided to follow the writeup here: scortes's 1996 Mazda 626 on CarDomain - Page 3

This guy calls the egr passage the pcv passage, and calls the idle air passage the egr passage, but other than that, it's a decent writeup. I broke the coolant connector because I pried on it too much, luckily a new one was less than $10 at the dealer (iirc). If you look at what he calls the pcv passage (actually the egr passage), that's what mine looked like's what mine looked like after:

Because the IM had already been put back on the car, I did it like this guy in the writeup, but instead of spraying anything into the egr passage on this side, I recommend scraping all the buildup out, because otherwise, the excess liquid goes all the way down the passage and into the egr, and then a few days later you get another code for the egr not working (trust me)...and getting the egr off is a b!tch, so trust me when I say that scraping the carbon buildup out is the better option. The spray doesn't penetrate through the buildup anyways. I posted these pics in another thread too (, but I thought I would start a new thread to bring more attention to this problem.
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thanks for the info on this... doing some research for my son... hoping this will help
Figured i would try posting the whole story to see what you guys think.

My son just bought a 1996 mx6 ls with 140,000 miles with automatic transmission. He got in the car in the morning and had a check engine light. He went to Autozone to check the code. On the way, the car, for a moment, hung up and would not shift past 2nd or 3rd. RPMs shot up then it shifted fine. It did not happen again. Autozone checked the code and said it was an intake sensor. Autozone dude sprayed some cleaner in the intake. He sprayed maf air flow sensor cleaner on the mas air screen. Car was off when he sprayed the cleaner and cleared the code thru the checker.

Check engine light went off and stayed off. He went to play golf. The car sat for 6 hours at the golf course. When he got in it to go home the check engine light had returned and the car was hanging up in 2nd/3rd again. It would not shift and just kept reving up. So he drove it home at about 35mph. He tried it a few more times later in the day, with the same result. He checked the tranny fluid to find it low, so he topped it off. Then tried the car again. Same result. So he took it to a shop. The tech said the code was for the map/boost/baro sensor. The tech said the car went into limp mode and it would not allow the car to go past a certain gear/speed. He called around and the part was not available from any of the parts stores. So he called the dealer and it was $350.

He found the part on Ebay, ordered it, installed it. Disconnected the battery to clear the codes.... Now the check engine light has stayed off for now, but the car will still not shift past 2/3rd. It just climbs in RPMs. He is taking it back to the shop now, but I want to know is this common with this sensor. Could the new one be bad and just not throw a code yet, but keep the car in limp mode?

So my question is this? Do the symptoms match the part failure? Could it be the sensor? Or could it be what I have read in searching... the passage to the EGR could be caked with carbon? Or willl carbon in the intake always throw a code! I want to try to help him, but he lives over an hour away. So any suggestions you have would be awesome. I hate for him to just change the sensor and neglect the passage if it causes the same symptoms.

Thanks you guys!
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Sounds like two separate issues to me. The egr passage blocked or not shouldn't affect the way the car shifts. I doubt the car would go into limp mode just because egr flow is disrupted. I could be wrong though. What was the exact code your son got read at Autozone?

The automatic mx6s are known to be trouble, you'll find thread after thread on this site about a bad auto tranny, my guess is that the tranny is on its way out, especially if he found the tranny fluid was low.

I had the code P0400 and that didn't leave my car in limp mode. Once you clear the code, I think it takes 3 trips with the same problem happening before it triggers an engine light, you won't see it come on right away for this kind of issue.
Yeah I did the same thing yesterday, I opened it up to find it so badly built up with grime and gunk in there it was incredible, isn't the best idea to spray tb cleaner into the actual intake because obviously yeah it'd just pull off all the grime in chunks and would just cause further problems, but scraping out all that stuff is a good way to go, i used some tb cleaner to help me get most of it off

Heres my picture of how it was when i opened it up, the side that i pulled off was actually almost twice as bad as this, but i didn't get a photo..

Pretty damn bad.. She runs alot cleaner now that i've cleaned it all up though :)
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Wow, that does look pretty bad...
Looks familiar. Just did mine a few weeks ago. It gets on these and the throttle body facing the same way.
Is this all coming from the EGR exhaust gases ? I didn't notice any change in performance, but EGR
systems seems happy.

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Yeah, I'm pretty sure it's all from just the EGR at this point. The PCV air shoots into the IM after this point.
I was having issues with getting the throttle body boot/ elbow off the TB inlet, but was able to with some help

However, now I'm at the next step...I've unbolted the TB and it starts to separate off, but it won't budge past half an inch (still on the bolts). I can see some hoses near the bottom that are in the way of some pieces attached to the TB. I know the information referred to above at
is supposed to help with taking the TB off, but I can't figure out the 'trick' he's using to take the TB off without disconnecting hoses. Am I definitely going to have to disconnect the hoses or can I do it without that? Would appreciate some input onto how to get it off...really feel like I'm almost there getting access to the EGR passage for cleaning. Thanks in advance for your help!
You have to disconnect the one hose with the quick-connect on it. You'll probably break the quick-connect while doing it because it's a 15+ year old piece of plastic, but you can buy a new one at the dealer, or most people just get rid of the quick-connect and use a ring clamp to secure it.
So I did eventually break off the heater hose quick connect and was trying to remove the TB plate... but it's still not coming all the way off the bolts(although the gap between the two TB surfaces is now about an inch. However now it's stuck on the bolts and is not budging in either direction(pulling and pushing like crazy doesn't seem to work).I can see the screw threads on the bolt towards the front of the car, but not the back bolt, and the plate at the back bolt is not moving at all, although the plate near the front plate can move back and forth about a mm or so. I'll run and get a mallet tomorrow to try and tap it off but I stupid question...are you supposed to unhook the accelerator cable? I'm trying to figure out why it's not budging anymore. I really hope i haven't bent the bolt or anything :(
Take it slow if you've never done car work before. Don't damage any very (very) delicate aluminum threads. Don't crack plastic pieces, after all these years they will break easy. Don't pry anything unless it's a last resort.

First, make extra sure you've removed all the bolts that are preventing separation of the parts. Get a printout of an IM removal guide, try to think of what you might be doing wrong before you go breaking something. Try to find the factory repair manual (it is not too terribly hard to locate a link via google) and see what info it can give you.

Spray some penetrating oil on the parts and let it sit. Get a plastic deadblow hammer (or something like it) and tap with some force all around. Spray more oil. Hit it again with a just bit of force but make sure the bolts are NOT ENGAGED WITH THE THREADS when you do this, i.e. they are backed out of the hole.

And, yes, you remove the accelerator cable. You use one hand to rotate the throttle cam it is attached to, maybe one half turn. Look carefully with a light and you'll see that on the end of the cable, there is a little metal cylinder that slides into a hole on the throttle cam goes around. You need to use your other hand to get the cable out of that little hole, you need to rotate that cylinder and the wire will clear a slot on one side of it and slide it on out. Voila.

You will need to install a new intake manifold gasket (set of two) along with a new throttle body gasket. With the intake manifold off, now is an *excellent* time to replace the two O-rings that are on the passengers-side end of the two metal coolant pipes that sit right smack in the middle of the engine underneat the IM. Those O-rings will leak coolant and ruin your knock sensor. You can get replacements at the dealer, or just find a "seal" shop in your town that has many different types of O-rings, if you live in a large city there should be one.
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Even though the throttle cable should be fairly easy to take off and on, it took me
quite a while to figure it out....!!

And I don't know about adjusting it, I guess that is fairly easy too.
Finally, I got all of this done. Got the TB off, cleaned off the insides with brake cleaner, and gouged out the stuff that was plugging up the EGR port (it was really gunked up!). I didn't do anything with the IM.
Took me a 2-3 weeks as I got busy, so my only worry was that after all the coolant spillage from disconnecting the heater hose that the cooling system may have gotten dry (and starting to rust) by sitting for a couple of weeks. I guess that's the next problem.
Putting it all back together was a breeze compared to taking it apart.No CEL since I put it back(it's been 4 days), let's hope it stays that way. I also changed the pre-cat oxygen sensors while I was at it. I needed to do all this to pass CA smog, which it just passed today...awesome. Hopefully, at least another 2 years with my 6...hopefully it doesn't die on me since it's pushing 190k miles.
Thanks for a great write up and help along the way on this thread, this is definitely a keeper.
Can you post all the figures for the CA smog test and your results, especially
the HC and NOx at both low and high rpm test ?

I just went for test and didn't pass in TX. Will post. Mine also has exactly 190k miles
on a 94.
Here's a link to my test results

For the first test, I had failed at the low speed of 15 mph. The day after changing out the O2 sensors and TB cleanout(and 20 miles of driving), the results got worse!

The testing guy told me to come back a few days later because the system takes time to get used to the new sensors? Came back two days later(and an additional 40-50 miles) and it was like a different car (although the high speed NO got worse)...and passed.

As a side note, the exact same thing happened to me two years ago when I went to get smogged...high HC and NO at low speed causing low speed fail. Switched out the oxygen sensors and voila, problem solved.
I have a new EGR valve, new 02 sensors, all new hoses, new catalytic converter,
and still am getting high numbers on the test:

Low rpm
HC 136 ppm standard 222 ppm result
N0x 1045 ppm standard 1222 ppm result

High rpm
HC 132 ppm standard 212 ppm result
Nox 945 ppm standard 1075 ppm result

Car runs good, premium fuel, timing is at good at 10 degrees. If you retard the timing
do you get better results ? No check engine light codes on.

I have never changed the PCV valve or those 2 hoses (the short one and the very long one going to the back of the engine). Can that be causing high HC and Nox ? Do those hoses get plugged or narrowed over time by the stuff
running through them ?

The new EGR valve helped a lot to lower Nox, but still not low enough.
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Aftermarket cats are not all the same, I specifically bought a California legal one to be sure that it'll get the job done...I've read many stories of mx6 owners failing with an aftermarket cat but passing with their old stock one.
I think I just need a better, or more expensive catalytic converter. Can you recommend
any brand ?

The HC is almost identical to last year, even with new EGR valve, new timing belt, etc.

Only other thing I can think to do is put in a new PCV valve, even though the one installed still rattles. I haven't ever replaced it in 10+ years.
I got the Magnaflow 46034 Universal Catalytic Converter from Amazon. This one has the O2 sensor in it though, you need a similar one without the sensor if yours is a 94 like your profile says.

A quick search on the Magnaflow site suggests a universal #36105 ($207 on amazon) or direct fit #36693 ($285 on amazon) for California legal.

For non-California, there's universal #91005 ($68 on amazon) or direct fit #23693 ($119 on amazon).

If you need a bolt-on solution, the $285 one is a good option. With that one, you'll be sure the cat isn't the reason you're failing.
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