Rough Idle/Intake manifold

[FrankD]

I recently had the Ontario clean air test done and they told me the intake manifold is leaking. The car idles roughly and seems to be gradually getting worse. Sometimes as the engine warms up it races up to 3500 rpm and wont drop to normal for about 10 minutes. Otherwise it runs good.

Is there a vacume test I can do to verify this?

Is taking off the intake pretty straight forward?

Should I remove the carb first..I know..I have to keep it upright!

Do the intake manifold studs tend to break?

Frank
89AccordLXcarb

[A20A1]

well you have to keep the float needle from falling out of the float valve. when you flip the carb the needle tends to come out. otherwise you can still turn the carb upside down if you needed to.

[BoredRec]

have fun if you do try to take off the intake manifold. Took me like 2 hours, and that's with a lift and air tools.

[DanG86LX]

Originally posted by FrankD
I recently had the Ontario clean air test done and they told me the intake manifold is leaking.
Just curios, how did they figure out that (a leak)? Do u know where the leak is exactly ? Cause u may take off the manifold just to discover that the problem is somewhere else..

[FrankD]

A service tech at a local garage told me the intake manifold was leaking after he performed a vacume test. He would not give me any more details so I'm not really sure if the rough idle could be caused by something else. I was hoping some members could describe symptoms of a leaking intake gasket. I get rough idle, kind of jittery while coasting below 50mph, engine racing when not fully warmed up.
Frank

[carotman]

just spray Carb cleaner on the intake manifold gasket where it mates with the engine.

if the engine reacts, you have a leak

[A20A1]

thats silly... a manifold vacuum leak doesn't have to be from the manifold... it could be from any of the vacuum lines tapped into the manifold.

[FrankD]

OK ! Now were getting somewhere! So spraying around the gasket should at least give me an indication if the gasket itself is the problem.

[FrankD]

OK I've got the air cleaner off and I'm checking all the hoses and diaphrams etc...There seems to be one thats seized. Its on the front and the plunger goes to a link on the left bottom of the carb. The vacume line goes to a T which splits off to a coolant temp sensor near thermostat and to carb. I can only move the plunger back and forth about 2mm. Its in the off state now. The other diaphrams move about 1cm. Anyone know what this diaphrams' for.

[A20A1]

thats the vacuum secondary... don't break the diaphragm trying to move the plunger? or are you using a hand vacuum pump?

[A20A1]

the secondary is locked by the primary throttle linkage... if you open the primary barrel by pressing the gas pedal then you can move the diaphragm arm freely

[FrankD]

Thanks Carotman for carb cleaner spray trick...you're my hero! It's amazing how 3 different mechanics could not figure this out. Scarry but true.

[Site]

"have fun if you do try to take off the intake manifold. Took me like 2 hours, and that's with a lift and air tools."

I got mine off in like 2 hours. I have no lift or air tools. I used a 3/8 in drive ratchet with a long extention and one of those cool adjustable/universal joint things that lets you hold the ratchet at an angle. It was difficult to do, though. Seems like this thing is a bear to remove whether you go at it from above or below.