Replaced intake manifold gasket and now the engine idles rough, dies

[thatoneguy]

2004 Corolla S Automatic

I knew from last winter that my intake manifold gasket was bad after the check engine light came on and the dealer told me the deal. I didn't take care of it then as spring was rolling around with warmer temps and the CEL went away, but the other morning it was one of those 9*F mornings and the check engine light came on. It took an extra second longer that morning for the car to start up, but it idled fine. The gas mileage had been dropping quite a bit though.

So knowing I needed a new intake manifold anyway I went to the dealer and picked up the upgraded orange one. I also gave them my VIN for a new PCV valve. Unfortunately, despite providing my VIN, they still gave me the wrong size PCV valve--the one in my car is bigger than the one they gave me.

Today, despite it being 5* with the windchill at -14*, I went to work on the Corolla. The first thing I was going to do was change the PCV valve as that seemed like the easiest task. But that's when I discovered the dealer gave me the wrong one. So on to the intake manifold gasket.

I followed most of the directions here http://toyota-solutions.blogspot.com...a-corolla.html and here P0171 - Intake Gaset Seal Repair - Tips except for one thing: I worked around the throttle body a little bit differently. I didn't realize this until after I came in from working on it, but I didn't remove the throttle body from the intake manifold. Instead, I removed the big black air hose off the throttle body and the metal arm that extends from the throttle body down to the bottom of the intake manifold. I was still able to wiggle the intake manifold toward me and rotate it out of the way enough to replace the original black gasket with the new one.

I put everything back together and went to turn the car on and it revved up around 2500-3000 RPM for a second before dropping to 1000-something and then it searched around in the 1000s for a few more seconds before it sounded like it was choking and dropped well under 800 RPM to the point that it sounded like it was going to die. I switched it off, loosened all the screws and tightened them back down, as well as glanced around to check that all the hoses were connected. I didn't see anything disconnected. I disconnected the battery for a few minutes and tried starting the car again--again, same thing as before.

So my question is, after trying to fix my air leak and apparently causing a bigger leak, where should I look for a problem? Could playing with the PCV valve have caused a problem? All I did there was wiggle the hose off and try to remove the old PCV valve but I couldn't because I didn't have a tool big enough for the old one (I wasn't expecting one so large). I put that hose back the way I found it.

What about the throttle body area? Could I have damaged something by leaving the throttle body attached to the intake manifold like I did? Any particular hoses I need to double check?

Thanks in advance.

[Tech1984]

There's a hidden vacuum hose you pulled off without realizing it. It's down under the back side of the intake below the throttle body.
It comes from the evap canister control valve. A strong light shined down there will show a hose nipple sticking out pointing to the engine. Black of course, hard to see.

[thatoneguy]

Originally Posted by Tech1984

There's a hidden vacuum hose you pulled off without realizing it. It's down under the back side of the intake below the throttle body.
It comes from the evap canister control valve. A strong light shined down there will show a hose nipple sticking out pointing to the engine. Black of course, hard to see.

Thanks so much for the reply, fingers crossed you're right and that I can find it tomorrow! Is the nipple going to be on the intake or on the throttle body?

Edit: And do you think I'll have to take the whole intake off again? Or just peak in there and hunt for the loose hose?

[Tech1984]

On the intake because it's a manifold vacuum supply. Worst case, just remove the throttle body to access it, however is doable being creative.

[invader]

Elusive brake booster vacuum hose fitting on the back of intake manifold near throttle body is in middle of photo...

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[thatoneguy]

Thanks so much guys, I'll report back tomorrow with what I find.

[boberic]

There should be a vacuum hose diagram on a sticker somewhere in the engine compartment. As well as checking that you've made all the connections, make sure they all go to the right place. I had an issue similar to yours and the dealer said I had one pair reversed. I wish I knew for sure if that was my fault or one of the crappy mechanics I let touch my car, but anyway after getting that set up the car more or less runs right now.

[thatoneguy]

You guys were exactly right, it was that vacuum hose on the intake under the throttle body. "Elusive" is an understatement. The throttle body on the 2004 has the arrangement of the 2 bolts and 2 nuts different than from what I've seen in other images like in those that I linked to in the original post. The two bolts were on the top of the throttle body and the two nuts on the bottom. This made it impossible to remove the throttle body from the intake without disconnecting all of those other coolant hoses--either there wasn't enough slack or the hoses were too cold to move around enough, either way I didn't want to force off. I was able to get the vacuum hose back on the intake by taking the intake off again to give myself just a slightly better angle at pushing the hose back on, which wasn't easy considering how cold every was.

Turned the car back on and it idled right around 1800, nice and smooth. Time will tell if the CEL comes back on after a few more cold soaks. Off to the dealer now to return that PCV valve for the right one.

[Tech1984]

Originally Posted by thatoneguy

You guys were exactly right, it was that vacuum hose on the intake under the throttle body. "Elusive" is an understatement. The throttle body on the 2004 has the arrangement of the 2 bolts and 2 nuts different than from what I've seen in other images like in those that I linked to in the original post. The two bolts were on the top of the throttle body and the two nuts on the bottom. This made it impossible to remove the throttle body from the intake without disconnecting all of those other coolant hoses--either there wasn't enough slack or the hoses were too cold to move around enough, either way I didn't want to force off. I was able to get the vacuum hose back on the intake by taking the intake off again to give myself just a slightly better angle at pushing the hose back on, which wasn't easy considering how cold every was.

Turned the car back on and it idled right around 1800, nice and smooth. Time will tell if the CEL comes back on after a few more cold soaks. Off to the dealer now to return that PCV valve for the right one.