So what does it take to crack the inlet manifold on a 172

[hostler]

Okay so I was installing a battery cover and decided to paint the ECU bracket. While working in the engine bay I leaned over the engine with my hand on the Renault Sport letters of the intake manifold. I heard a little sound which almost sounded like a crack or something but it didnt sound like anything bad or a sound that aluminium usually wouldn't make when there's some weight on it. Ever since then it idles at like 2000 rpm. When driving and pressing the clutch the idle will jump up and down from around 1200 to 1900/2000 rpm. There's also a very very slight hesitation when opening the throttle body by hand. It sounds like the revs drop a little bit and then it picks it up.
I've had the ICV replaced about 2 years ago with one from VDO so I doubt it could be that.

Stuff I had disconnected while leaning on the intake:
Battery
Intake before throttle body
ECU connector

I honestly doubt there's anything wrong with the connector on the ecu as there's no lights on the dash and the car runs great.

So I've checked the following:
ICV to intake elbow
Throttle body to valve cover breather
Inlet manifold to brake booster

All the hoses and hose clamps seemed fine.

So does this sound like a possible crack in the inlet manifold? Or should I be looking elsewhere.



It may not run right but at least the engine bay is pretty

 

[scullyg40]

Probably look elsewhere. I lean on it all the time. It's also supported at the lower intake, and at the back near the coil pack.

 

[scullyg40]

Just saw pictures in your thread, but you don't seem to have the 2 bolts at the back of the intake?

 

[JamesBryan]

Doubt you'd be able to crack it like that, they're quick thick.

Must be something loose somewhere.

Have you tried torquing all the inlet bolts up to 12nm?

 

[hostler]

Just saw pictures in your thread, but you don't seem to have the 2 bolts at the back of the intake?

I just checked, all bolts are in.

Doubt you'd be able to crack it like that, they're quick thick.

Must be something loose somewhere.

Have you tried torquing all the inlet bolts up to 12nm?

I don't have a torque wrench but there isn't any harm in checking the bolts. Will try that later.


The thing is though, I haven't touched the inlet/intake manifold or throttle body and it was fine before.

 

[Krarl]

Check your gaskets and pipes. I'm pretty sure you could volley a 172 upper inlet off tower bridge and it'd still survive 😂

 

[Louis]

Air leak somewhere by the sounds. Get some butane and listen for a change in tone at idle when you move it around the engine.

 

[hostler]

Air leak somewhere by the sounds. Get some butane and listen for a change in tone at idle when you move it around the engine.

Will try this tomorrow. It would just be a case of listening for a change in rpm? Like lower?

 

[JamesBryan]

Brake cleaner works too, it just seals up the air leak for a second so that you can pinpoint the leak.

 

[hostler]

I couldnt find a blow torch anywhere so I didnt get to test it using that method. I did spray brake cleaner around all the areas that could possibly have a leak but I couldn't find anywhere. Checked all the inlet bolts and everything is tight. I disconnected all the hoses that could possibly have a leak. I even suspected the brake booster having a leak since its a little rusty at the bottom but I disconnected that and plugged it off at the intake side and that didn't change anything either.

Something that's a little weird is that when I start the car it idles high but when I plug the ICV completely it idles like it's supposed to and then it will keep doing it. See this video:


I also removed the ICV hose completely and sealed it at the ICV which resulted in the exact same as in the video.

Since I closed the ICV with my fingers completely, doesn't that mean that it's pulling too much air from somewhere else? Isn't the idle supposed to be horrible when you plug it? It seems to want to idle around 1800/2000 rpm when the engine is a little bit warmer. Its around 1100/1200 rpm on cold start.

 

[hostler]

Still at a loss what it could be. Would love to hear if anyone agrees with my above post that the ICV is fine (since it idles better, but still at 1100/1200rpm, when blocked off completely)

Ordered all new gaskets for the intake from Renault which I should be able to pick up later this week.
Renault Clio 172 182 Inlet Manifold Seal - 8200052311
Renault Clio 172 182 Inlet Manifold Lower Gasket - 7700109906
Renault Clio 172 182 Inlet Manifold Gasket - 7700114203
Renault Clio 172 Throttle Body Gasket - 7700866483

 

[Bankrupt_drunk]

Not too sure what to suggest, but I'm also experiencing dodgy idle when cold. Like you ive checked all the hoses, changed the gaskets, and re-torqued the head bolts. The only place i could think it could be leaking was the map sensor, as it seemed loose.

 

[hostler]

Replaced all the intake gaskets except the lower one where the RS stamped one meets the head as I was hoping to be lucky. Well I wasn't. Still having the exact same issue. On cold start it will sit around 1200 rpm. Once there's some heat into it and you come to a stop it will sit at around 1900/2000 rpm.

Should I be looking at some kind of sensor? I dont see how the gasket of the lower inlet that attaches to the head could've suddenly gone wrong.

 

[Krarl]

MAF and MAP defintely not really loose or shagged? No ICV leaks or issues?

 

[hostler]

So I did end up finding the problem. I've replaced most of the gaskets which wasn't it. Replaced the MAP and air temp sensor, that also wasn't it. I didn't think it could be the throttle body but since i had recently sent a spare one off to get enlarged and refurbished I just chucked that one on and to my surprise this fixed the problem. There must've been some wear on the shaft in the throttle body causing it to not seal correctly.