P0400= Blockage in intake manifold

First post, I hope this is the best sub-forum for it. I've kept the wife's 97 Postal legacy 2.2L going for 380k miles so far, and it runs well, but have had ongoing problems getting rid of the P0400 code prior to inspection over the past few years. Generally, I've cleaned and/or replaced vacuum hoses, the EGR valve, the EGR pipe, the BPT, and the ports in the head and the intake manifold that the various EGR parts attach to.

 

This year I haven't been able to get rid of the code. Reading some of the P0400 posts on this and other forums, I did some diagnostics and found that manually activating the EGR valve does not change the idle. Removing the EGR valve, I found that the exhaust gasses are exiting the opening, but there is no suction on the intake manifold. I'd already cleaned that opening out as far as I could see and now am trying to clean out the passage in the intake manifold which appears from the outside to have several substantial turns in it Broke off and thankfully managed to retrieve a small wire handled bottle brush in there. I've been using denatured alcohol as a solvent. Anyone have any suggestions? Anyone familiar with the inside of the intake manifold? Is there any sort of screen, baffle, or valve that would explain this blockage?

have you tried spraying carb cleaner all around the vac hoses as the engine sits idling? if the cleaner is sucked in to the intake it will / could / should rev the idle.

 

i have never heard of any type of blockage in the intake causing a p0400. much more likely causes are vac line leaks or possibly the small inline filter between the intake and the passenger strut tower. it is usually located parallel to and maybe ''zip tied'' yo a large black hose 1+ inch in diameter.

 

what have you replaced, tested, and cleaned?

Thanks for the response. I'm pretty certain there is a blockage in the intake manifold because the EGR valve opens when I rev the car. (It does close right away, don't know that it is supposed to do that). When I removed the EGR valve (replaced last year and thoroughly cleaned this year) the idle didn't change and exhaust gases came out of the appropriate port. A lit match in front of the intake port did not waver. There is a small square drive plug in the manifold above the EGR valve. When I removed that it sucked air and the idle dropped almost to stall.

 

To answer your questions. In the past two years I've replaced all of the vacuum hoses, the BPT, the EGR valve, and the EGR solenoid. I removed and thoroughly cleaned the throttle body, EGR valve and EGR pipes this week. It took a whole spray bottle of cleaner and a lot of compressed air. I checked and all of the hoses were clear. I cleaned the idle control valve a couple of years ago.

 

It is an automatic and I checked resistance in the pressure control solenoid and valve on the wheel well (replacements are quite expensive and there is no indication they are the problem). The in-line filter is in the UPS system as we speak, but I bypassed it when I bypassed the metal pipes near the throttle cable last week. I will try using Seafoam in the intake as a last resort but with such high mileage on the engine I'm concerned about stressing it.

 

I remember from when I had the throttle body off that there is a cylindrical projection coming up from the bottom of the manifold. It has an indentation in the top that had carbon/tar on it. I probed the indentation briefly but was hesitant about using too much force on an unknown. I wonder now if that is where the channel from the EGR valve ports into the manifold?

your knowledge of this system is much more than mine. but given what you have done in recnt years and your confidence in a blockage, have you considered replacing the entire intake? (95 - 97 with EGR, usually from an auto trans car.) you could swap in any new parts you have installed recently.

 

some here will have one or look on www.car-part.com use you zip and distance to find one close to home, about ~$65.

Thanks. I'm thinking I will put a new manifold on if I can't get this one cleaned out. The expense of the part isn't a problem, but I dread having to remove the manifold. In my experience, when working with older cars the hassle factor in frozen, broken, stripped etc parts can be fierce. If I end up taking the manifold off, I might just have to go all the way and do a ring job since the blow-by seems to be an increasing issue in oil usage and systems fouling. I bought another can of throttle body cleaner today, a wire brush kit and a $100 camera scope at Harbor Freight. Can't wait for my wife to get back from her mail route today and start a 3 day weekend. I wonder what I'll be doing in the 90 degree heat for the next day or two? I bought new spark plugs and wires for the '91 in case she needs to drive it for the next couple of weeks while I'm rebuilding the '97s engine

 

And I think if my knowledge of this system was much greater than yours, I would have done some diagnosis and figured out the blockage before "throwing parts at it."

there isn't much to the intake removal, 8 bolts, unplug some connectors, disconnect the fuel lines and the charcoal canister in the front.

 

the EGR pipe may be a challenge but at least you can reach it and you undid it when you replaced the valve. and there a 2 hoses under the throtle body that are a pain, but if you unbolt it and lift it a bit they are easier to reach. or cut them and buy generic replacement hose.

in my exsperience the 8 intake bolt are a easy task, you should have anyproblems when them, they are not studs with nuts so if you do break them you should have enough of the bolt showing to get them after you pull the mani. plus if you cant get one they are not very important. 3 bolts a side would probably do fine.

Berryman's B-12 sprayed into that hole you exposed in the intake manifold that should have vacuum but doesn't. Let it sit for a few minutes and then blow it out of there with compressed air. I took the tip off of my spray nozzle and JB Welded a 12" piece of brake line in there. I now have a bendable spray nozzle that gets into tight orifices.

 

After you spray clean out that little hole, soak it with more B-12. Eventually you will desolve all that hardened crap out of there.

 

On other engines, sometimes you have to do the soak blow soak blow process from the inside end in or near the throttle body.

 

On other engines, there are removable plugs that allow you straight-in access to the EGR's complete passageway.

 

The buildup is caused by hot, oil and soot laden exhaust gases that are sucked into the engine for pollution reasons, condensing on the relatively cooler intake passageway.

 

The same thing happens with Crankcase gasses that are sucked into the engine by way of the throttle body area.

 

Tom

It so happened that the B-12 was the solvent I selected at the parts store yesterday. The can is empty now and and compressed air blows through the passage. Turns out that the cylindrical projection inside the manifold is the port for exhaust gases. It has a hole in the top of it in the center of the hemispherical depression. I went at the blockage from both ends with the B-12 soak followed by compressed air through a piece of vacuum hose on the EGR valve end. The red tube from the B-12 fit into the hole in the manifold projection after I opened the hole with B-12, q-tips, and a piece of wire. The red tube from a can of wd-40 fit nicely into the hole and into the end of one of my compressed air nozzles. I'm letting it all air out now. Will reassemble it shortly, drive it until the OBD tests run and then hopefully go to the inspection station.