Finding a Leak in the Intake System

[WIL35]

On a 2003 Avensis Verso with 187k miles on it; the car is suffering from shuddering and nearly cutting out. It has new spark plugs, MAF sensor, air filter and I have checked the inlet system from the air filter to the throttle body, which I have also cleaned with carburetor cleaner. It recently passed its MOT, so emissions must be within tolerance.

Given the way the revs drop, it feels like the mixture is too weak, which could point to a leak on the inlet side. Apart from visually, is there any other way to check how airtight the intake system is? The inlet manifold is, unfortunately, quite inaccessible around the back of the engine.

Thanks

[PositronicRay]

You could try squirting some brake cleaner around the place, if the revs change you've found the leak. I spent ages trying to find a leak recently then traced it to a sticking purge valve.

I would have expected an intake leak that bad would have put on the EML light though.

[GreenV8S]

Is the ECU reporting any faults?

Does the problem go away at full throttle?

Does the problem vary with throttle, revs, engine temperature or anything else?

Does it happen consistently under the conditions that provoke it, or is it intermittent?

Edited by GreenV8S on Friday 30th June 11:47

[fatjon]

A drop of diesel in a syringe also works. When smoke comes out the back you have found the leak.

[WIL35]

Thank you for the responses

The car falters quite badly when accelerating, it is fine once at a steady speed and throttle.

Have had the car since new and the EML came on at about 60k miles, code p0420 and p0430 I think. I changed all the O2 sensors (pre and post cat) and the light came on again after a few hundred miles. I then investigated and found out that this was quite a common ZZT engine occurrence that would need an ecu update to clear. I've done all the servicing and repairs on it and as it kept passing MOTs, ran fine and was clearly just a software glitch, I didn't bother taking it to the dealer.

It has been fine for the following 120k miles, up until now. I did change the O2 sensors again recently as I figured they could be 'worn' again. I think I need to try and get to the intake manifold and see if any of the bypass hoses have split or perished. I think the manifold is plastic, so could have a split in it.

[GreenV8S]

If it's worse at wider throttle openings, that seems less like an unmetered air leak and more like a weak spark or some other fault causing misfueling.