Intake manifold (Page 1/1)
Benster SEP 25, 09:59 PM
Hey, I just learned I've got a issue with my lower intake manifold (I've got a 1985 GT), as I've been loosing a bit of coolant, and getting a check engine light for intake manifold air temp, if anyone has tips on how to do the job it would be very appreciated, as I cant find any good videos that go all the way down to the lover manifold, and I'm new to personal car repair in general. Anyways, any insights or videos or written guides would be appreciated, thanks.
Patrick SEP 25, 11:47 PM

quote
Originally posted by Benster:

...getting a check engine light for intake manifold air temp



Unless you know for a fact that there's something wrong with your upper, middle and/or lower plenums, I wouldn't be taking them apart for a trouble code indicating a problem with the Manifold Air Temperature sensor. I'd suspect the sensor itself, or perhaps even its connection to the harness.

What makes you suspect a problem with the lower plenum? Is there coolant getting into the crankcase, or into one cylinder?
Raydar SEP 26, 10:03 AM

quote
Originally posted by Benster:

Hey, I just learned I've got a issue with my lower intake manifold (I've got a 1985 GT), as I've been loosing a bit of coolant, and getting a check engine light for intake manifold air temp, if anyone has tips on how to do the job it would be very appreciated, as I cant find any good videos that go all the way down to the lover manifold, and I'm new to personal car repair in general. Anyways, any insights or videos or written guides would be appreciated, thanks.



First... the intake air temp sensor is in the "firewall or fender" side of the air filter canister. That's about two feet before the intake manifold.
As suggested before, look at the sensor (is it missing?) or the wiring that goes to it.
If someone has removed or modified the air filter canister, there is a chance that they just removed the sensor, too.

Fieros are not really known for intake manifold coolant leaks, unless they've been grossly overheated. But there are lots of places they can lose coolant. Check the front radiator cap, and the rear thermostat cap.
Check all the pipe-to-hose connections, near the engine, and near the radiator. Don't overlook the heater hoses. The water pump also has a weep hole. If that leaks, it can leave a puddle under the right rear of the car.
If you're not burning coolant (you'd have sweet-smelling white clouds from your exhaust) or seeing coolant in your oil (think "mocha" milk shake, or at least water droplets on the inside of your oil cap) I wouldn't worry about intake gaskets.
Don't be confused by water vapor from condensation, from the exhaust. That will go away once the engine is warmed up. Burning coolant likely won't go away.
Benster SEP 26, 05:39 PM

quote
Originally posted by Raydar:


First... the intake air temp sensor is in the "firewall or fender" side of the air filter canister. That's about two feet before the intake manifold.
As suggested before, look at the sensor (is it missing?) or the wiring that goes to it.
If someone has removed or modified the air filter canister, there is a chance that they just removed the sensor, too.

Fieros are not really known for intake manifold coolant leaks, unless they've been grossly overheated. But there are lots of places they can lose coolant. Check the front radiator cap, and the rear thermostat cap.
Check all the pipe-to-hose connections, near the engine, and near the radiator. Don't overlook the heater hoses. The water pump also has a weep hole. If that leaks, it can leave a puddle under the right rear of the car.
If you're not burning coolant (you'd have sweet-smelling white clouds from your exhaust) or seeing coolant in your oil (think "mocha" milk shake, or at least water droplets on the inside of your oil cap) I wouldn't worry about intake gaskets.
Don't be confused by water vapor from condensation, from the exhaust. That will go away once the engine is warmed up. Burning coolant likely won't go away.



I'll check that, my oil is clear but the exhaust has a sweet smell with smoke, and I've lost coolant and it hasn't been on the ground under the car, and that combined with the check engine code makes me think it's the lower part of the intake manifold, and I'm the second owner and I've got no idea how poorly the car was treated beforehand, so it's possible that the leak is from overheating.
sleek fiero SEP 27, 11:23 AM
You are burning coolant. I would borrow a coolant pressure tester and take the spark plugs out. Pressure up the system and wait and see if pressure drops. If it drops try cranking the engine over and see if it blows coolant out of a plug hole. If it does blow coolant then you probably need to remove heads and replace the gaskets at a minimum. sleek
Raydar SEP 27, 06:30 PM
You might very well have a coolant leak into the engine, but the Intake Air Temp sensor code has zero to do with that.
And fixing the leak should not make the code go away.

With that said, I found a blown head gasket by rotating my engine to the compression stroke on each cylinder, and connecting an air compressor through the spark plug hole. Most compression testers have a removable hose that can be adapted to connect to an air compressor hose, using a simple "air tool" fitting.
It might sound like a bad idea at first, but most air compressors don't do much more than 100-120 lbs. Most compression tests show 140+ on a healthy engine. So you won't hurt anything that isn't already hurt.

Remove the thermostat cap and thermostat. Take your spark plugs out, and connect to each cylinder, in turn, in "firing order", on its compression stroke. Air bubbles from the thermostat neck will tell you which cylinder is leaking.

This method worked for me, while a compression check was quite inconclusive. (I had a blown head gasket, due to a broken head bolt. But my engine would idle all day long without using any coolant. If I floored the gas, while driving, it would blow all the coolant out through the overflow bottle. You can try that, too.)

[This message has been edited by Raydar (edited 09-27-2025).]

Dennis LaGrua SEP 28, 03:50 AM
How many original miles on the engine? If your problem is the head gasket leaking, you can try Bars Leaks head gasket sealer. Its not the best way to fix the problem but it will buy you time, and get you back on the road. A friend of mine used it on his Chevy Traverse and it lasted two years of daily driving before he pulled the heads, had them resurfaced and put all new gaskets in place.

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