changed intake gaskets, now high idle

aar0s · Jul 6, 2010

Like the title says, me and a friend changed the intake gaskets yesterday i go to finish buttoning up and changed the oil, fired it up and have an idle that around 1500 to 1700 rpms. I dont think that its a leak around the intake, everything there is snug, vac lines all looked good, the only things i can come up with is i either got the throttle cable in a bind somehow or somewhere along the way i adjusted the idle screw to compensate for a bad idle caused from the vac leak from a shot intake gasket that been replaced and dont remember doing it.
any other ideas? :shrug:

jrichker · Jul 7, 2010

A vacuum leak is the most probable cause of your problem. The head to manifold gaskets are prone to slipping out of place when you put the intake manifold back on. See http://www.stangnet.com/mustang-forums/795959-high-rpm-control-computer-2.html#post8246006 for someone else who had the same problem. The next post after that is my fix for the problem.

Otherwise, see the "Surging Idle Checklist for help with all your idle/stall problems. Everything you need to find and fix idle problems is in there.

The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

stykthyn · Jul 7, 2010

vacuum leak. its possible you pushed some of the rtv out when you tightened it down. Did you wait for it to cure before you started the car?

aar0s · Jul 7, 2010

Yeh it was cured, the car sat over night so i would hope it was cured. used the supplied rubber rubber end pieces with a good sized glob of rtv at the corners and the 3m method that jrichker talked about in the thread he linked then snugged everything down tight. It would take a bipartisan act of congress to move that gasket after that **** set up. both surfaces were smooth and cleaned with starter fluid (its the only thing we had on hand) and waited a few min. for that to air dry. put the upper on but we were running out of time so its possible that its sucking air between the upper and lower. plus the wireing behind the egr just dont look "right" like maybe somethings out of place. ill try to get the upper pulled tonight and see if we didnt get something like a wire between the manifolds.
Usualy i can pull the connection for the egr without taking it off but now there are wires in the way so something is out of place.

aar0s · Jul 7, 2010

This is me hoping for the easy fix. I started to take the upper off and noticed that it sort of kicked up when ever i loosened the bolts. started digging around the passenger side and found that the coolent line that runs back to the heater core was off its stud and pulled back enough to nearly be sitting on the valve cover pushing everything else over with it. thats why all the harneses looked wrong behind the egr valve. I checked the gasket and found that the two middle runners on the passenger side didnt have a good imprint of the manifold like the others did. im thinking that was where it was sucking air in at. ill get some help tomorrow and try to get that thing set on straight (unless someone knows a way to hold the gasket and lower the intake at the same time) and try it again.
btw, my heater core is out, i have no intentions of fixing it seeing that it dont get driven in the winter and the 2 or 3 times it does i dress accordingly. is there anyway to get rid of that coolent line? it has a sensor in it (im guessing the act) but couldn't i put that in the hole where the line goes into the lower intake? its a cobra intake so i dont need the egr lines either.
also, i found another hose laying loose up by the injectors that looks like it runs down to the charcoal canister, I dont remember unhooking it. where does it go to?

aar0s · Jul 8, 2010

alright, i put some rtv black on the back side of the gasket and let it set overnight with a shirt and a brick on it and today i was able to set the upper on it with no problems. got everything hooked back up and turned the key - nothing. damn batter is shot. was able to get it to start by jumping it off my wifes 01 that is sitting next to it and it idled perfectly. live and learn, when you think your ready to button something up triple check everything before you do so you dont get the frank above the beans like i did here!
Thanks for pointing me in the right direction, guys!
now, if i could get my gears installed id be a happy kittah!

Liv2roc · Jul 8, 2010

you dont say if it is carb or fuel injected. I had a 88 gt do that when it had a bad throttle position sensor

aar0s · Jul 8, 2010

My bad, this was on my 88 so it would be FI.

jrichker · Jul 9, 2010

Charcoal canister plumbing - one 3/8" tube from the bottom of the upper manifold to the rubber hose. Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid valve connects to one side of the canister. The other side of the canister connects to a rubber hose that connects to a line that goes all the way back to the gas tank. There is an electrical connector coming from the passenger side injector harness near #1 injector that plugs into the canister solenoid valve. It's purpose is to vent the gas tank. The solenoid valve opens at cruse to provide some extra fuel. The canister is normally mounted on the passenger side frame rail near the smog pump pulley.

The purge valve solenoid connector is a dangling wire that is near the ECT sensor and oil filler on the passenger side rocker cover. The actual solenoid valve is down next to the carbon canister. There is about 12"-16" of wire that runs parallel to the canister vent hose that comes off the bottom side of the upper intake manifold. That hose connects one port of the solenoid valve; the other port connects to the carbon canister.
Purge valve solenoid:

The carbon canister is normally mounted on the passenger side frame rail near the smog pump pulley.

Carbon Canister:

aar0s · Jul 9, 2010

yeh i figured that out right after i got the TB bolted back up, on of those "oh yeh, i remember that" moments.
how about getting rid of the coolent line and relocating the sensor to the front of the lower where the coolent line bolts in? how would i go about doing that.

jrichker · Jul 9, 2010

There is a big brass fitting that does the trick. It screws into the intake manifold water passage and then the ECT sensor screws into it.

Unfortunately, I don't have any details other than someone here on Stangnet posted a picture showing that they did it.

aar0s · Jul 9, 2010

Ill do some research and let ya know, you can add it to the vast knowledge you have on these cars.
little side story. me and the FIL were looking at the car after everything was said and done, kinda like guys looking at a grill full of meat. anyway, he notices that i have a wire off the solinoid (small red wire on the hot side) thats about to come off the connector, so he decides to fix it. the only end he can find is off an old fuseable link thats not being used anymore, splices that in there and said "maybe we should have found out where that wire went". tonight im driving the car to the store and go to roll up the windows. windows and locks dont work, guess the link was bad and so there is something else that gets to get done twice!

jrichker · Jul 10, 2010

One of the two will have the correct wiring for the windows & door locks for you car....

Starter solenoid wiring & fuse links

Regular starter on 86-91 Mustangs:

High torque mini starter or 92-93 Mustangs.

Diagrams courtesy of Tmoss & Stang&2birds

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