How To: TB & IAC Coolant bypass and block plate - Honda Prelude Forum

dohcpower v2.0 · 04-02-2003, 06:54 PM

Ok.. it is almost summer. No more cold weather. Time to do some free mods to help the car
stay cooler this summer. How about re-route the coolant lines to bypass the throttle
body, and IAC then make a block plate for the throttle body to eliminate irratic idle!

Tools:
10mm socket
12mm socket
flat tip screw driver
tin snips
drill w/ 15/64"s drill bit
needle nose plyers

Materials:
sheet metal
RTV hi temp silicone
3 small 10mm bolts

Time and Difficulty:
30-60 minutes / if you can remember and work a wrench, you're set!

Before you start:
Make sure the car is cool. Ther will be some coolant that leaks, and if the car is hot, you
could get burned. I'm adventerous, so i like to play with hot coolant!

Step 1
Remove the radiator cap to relieve pressure in the coolant system. Take off the coolant line
that is the farthest back, that is on top of the rear waterneck. Some coolant will spill from
this line, so be careful.

Coolant line removed

Step 2
Now remove the remaining coolant line that runs from the front port to the throttle body, from
under the throttle body. Now plug the end that was in the throttle body, into the rear port that
you removed the line from in step 1. Bascially, you are routing the coolant in a circle. You
can also remove the lines that are no longer in use from the IAC(on front side of intake manifold)
It is sometimes easier to remove the IAC to get the lines off unless you have a nice set of
angled plyers.

Coolant routed in circle

Step 3
Remove the intake from the throttle body. Remove the TPS harness(rear of throttle body), the
MAP sensor harness(on top of throttle body), and the vacume line.

Throttle Body almost ready to remove

dohcpower v2.0 · 04-02-2003, 06:54 PM

Step 4
Press the throttle rotor down. Pull the throttle cable out of the ridge of the rotor ,and let
the rotor go. You should be able to remove the pin, and place the cable aside. Make sure the
cable does not get bent. Remove the 2 12mm bolts, and the 2 12mm nuts. There is one wire harness
clip on the underside of the throttle body as well. I took tin snips, and cut it.

Throttle body out of car. Fast idle valve is on the underside

Step 5
Remove the 3 long 10mm bolts from the underside of the throttle body to remove the fast idle valve.
With the valve removed, there are 3 ports exposed. These are the ports you must block to prevent
erratic idle.

3 10mm bolts to remove

3 ports to be covered up

Step 6
Cut your piece of sheet metal to cover the surface of the bottom of the throttle body. Make sure
it is large enough to have all bolts go threw it. Place the fast idle valve on top of your
sheet metal. Use a nail, and a whackin device to mark the bolt holes. Drill the bolt holes, and
match up with the underside of the throttle body to make sure everything lines up properly.

Sheet metal cut to size

Marking Holes

Holes drilled

Making sure bolt holes line up with throttle body

dohcpower v2.0 · 04-02-2003, 06:54 PM

Step 7
Use the RTV silicone, and trace around the three holes. This will ensure a proper seal, which
should be pretty durn close to air tight. If there is a leak, you'll have a greater chance of
getting an erratic idle. That is NOT fun. Place the sheet on top of the sealent, and using your
smaller 3 10mm bolts, bolt down the plate. **You don't need to leave off the valve. if you can't
find 3 smaller bolts, or you want to have the car look factory, just place the metal between the
valve and throttle body!**

Sloppy, but does the job

Find 3 smaller 10mm bolts

Plate installed and ready to go back in car

Step 8
Place throttle body back in car, and re-install. This should be the opposite of removal. If you
can't figure out how to put it back in, then you shouldn't be doing this mod!

Fast Idle Valve Graveyard

Back in car w/o fast idle valve

Step 9
Let the sealent on the plate cure for 30-60 minutes. You don't want any of that junk getting into
the vacume system, or into your engine. Once it had dried, make sure everything is connected
properly, and start the car. Let it warm up, and listen for any erratic idle. The idle will
bounce badly if there is a problem. If there is a problem, you probably didn't seal the plate
well enough.

If there is no funny idle, then you are good to go! Be proud of your free mod. It will help
keep your car cool this summer, and maybe add a little power.

sharkcohen · 04-02-2003, 07:14 PM

There is nothing wrong with running this mod during the winter if the fast idle thermovalve is blocked. I've had this mod during sub 30 F weather with no idle issues at all.

Very nice writeup. Your block off plate looks like ass

G_Loc · 04-02-2003, 07:14 PM

nice

its not really necessary to remove the TB though. I was cheap and in a hurry so I used a piece of cardboard from a nutrigrain box, lol.

kennethmina · 04-02-2003, 07:14 PM

Nice!!!!!!

Since I will be doing the EGR block plate mod. I might as well do this at the same time.

Thanks.

marcucci · 04-03-2003, 07:12 AM

Ummm... not only is it easier to ditch the snips and go with gasket material, it's much easier. Cut a gasket the size of the valve and install it between the valve and TB. IT blocks off the passages and problem solved. Just make sure the valve and TB are dry (no coolant left). A cereal box works well if you can't find gasket material.

The sheet metal will get deformed with the snips, it might be tough to get it to seal even with RTV. I would suggest a "real" plate if you want to plate it off.

DudewithaLude · 04-03-2003, 09:37 AM

my cereal box gasket has worked well for over a year now

sharkcohen · 04-03-2003, 05:29 PM

There is no reason not to just use cardboard between the fast idle valve assembly and the throttle body. All the "gasket" is blocking off is air flow, sicne the coolant no longer flows through it. I have a Kellog's Special K gasket.

khilgers · 04-03-2003, 06:04 PM

are you guys serious about the whole cereal box thing? it seems like your joking, but not really

G_Loc · 04-03-2003, 06:05 PM

well his method makes it look cleaner since he completely took off the fast idle valve...

I may just use some 5mm aluminum I have lying around and do it this way to get rid of that crap.

khilgers · 04-03-2003, 06:06 PM

Also, is it really necessary to do the TB block off. I mean I will still see some benefits from the coolant bypass right?

dohcpower v2.0 · 04-03-2003, 06:19 PM

Quote:

Originally posted by G_Loc
well his method makes it look cleaner since he completely took off the fast idle valve...

I may just use some 5mm aluminum I have lying around and do it this way to get rid of that crap.

i've done 3 h22 throttle bodies, and did it on my g/f's 88 legend w/ the sheet metal, and i haven't had any problems yet. I just don't like the idea of having that valve down there, w/ open ports. Just looks better w/o it. Plus weight reduction!

dohcpower v2.0 · 04-03-2003, 06:20 PM

Quote:

Originally posted by khilgers
Also, is it really necessary to do the TB block off. I mean I will still see some benefits from the coolant bypass right?

You'll need to block the fast idle valve, or you will get a horrible erratic idle that will drive u nuts.

khilgers · 04-03-2003, 06:28 PM

^^gotcha....we don't want that

4bidden · 04-03-2003, 06:47 PM

I think I've asked this before.....

Would anyone be interested in a "kit" made up of an EGR block plate, a plate to seal off the fast idle valve, and one for the bottom of the eacv on the front of the IM? I'm thinking just some lightly polished aluminum for pretty cheap. It will make it a lot more simple.

eu4ik · 04-03-2003, 06:50 PM

i oughtta do this before the track tomorrow

sharkcohen · 04-03-2003, 06:54 PM

Quote:

Originally posted by khilgers
are you guys serious about the whole cereal box thing? it seems like your joking, but not really

Quite serious. I'm not joking when I say that I have a Kellog's Special K gasket. I wouldn't kid around about that

Dotay · 04-03-2003, 10:51 PM

Quote:

Originally posted by 4bidden
I think I've asked this before.....

Would anyone be interested in a "kit" made up of an EGR block plate, a plate to seal off the fast idle valve, and one for the bottom of the eacv on the front of the IM? I'm thinking just some lightly polished aluminum for pretty cheap. It will make it a lot more simple.

I'd be interested, how cheap? Under $20 and I think I would be down.

khilgers · 04-03-2003, 10:58 PM

^^I'm in too