Slight Lumpiness At Idle, Any Thoughts?

[The-Acre]

I've noticed for the past couple of days a very slight lumpiness in idle. It's only small but definitely noticeable. If I touch the accelerator a little to raise the revs it's fine. I had new plugs etc earlier this year. I'm sure it can't be related but I also noticed that my air con is "surging" Not affecting the engine speed but the air flow, it comes every 3 seconds or so. The air con is now working OK. The engine lumpiness also happens with or without the air con being on. Any thoughts on these two would be appreciated.

Phil

[The-Acre]

I've noticed for the past couple of days a very slight lumpiness in idle. It's only small but definitely noticeable. If I touch the accelerator a little to raise the revs it's fine. I had new plugs etc earlier this year. I'm sure it can't be related but I also noticed that my air con is "surging" Not affecting the engine speed but the air flow, it comes every 3 seconds or so. The air con is now working OK. The engine lumpiness also happens with or without the air con being on. Any thoughts on these two would be appreciated.

Phil

Surely someone has an idea of what the problem may be. And when I say the air con is working fine, by that I mean it blows nice and cold, but the blower is still surging today. The engine is still not as smooth as it was, although fine past idle.

[bigegg]

AC compressor is binding slightly, reducing engine power at low revs.

Not enough to affect at higher revs.???

That's the first place I'd check

Just a guess.

[The-Acre]

AC compressor is binding slightly, reducing engine power at low revs.

Not enough to affect at higher revs.???

That's the first place I'd check

Just a guess.

Interesting thought. It does seem that somehow the two are linked. Something else I've noticed is that when I put the air con on, or just the blower, it whistles like the air is squeezing through a small gap for a second or two. £££'s I think!

[dave1]

Is it only when the AC is on that it is not running correctly?

[ChrisM]

Have you tried cleaning the AC cabin filter to see if this affects this surging ?

It is suprising how much dirt and debris can get into this filter.

Also have you tried changing to recirculation mode to see if that changes anything.

I never turn my AC off, it has a thermostatic control which decides if cool air is required or not.

In winter it helps to clear the front screen.

[The-Acre]

It's not right even with the AC off. I have changed the cabin filter in the last month or so. It seems as though the air is having to pass through a space that's too small if that makes sense. Getting to where the blower is doesn't look like it'll be much fun either!

[dave1]

If the engine is the same with AC on or off then I would think it unlikely that the AC is responsible for any lumpy running. Have you got a dealer or trusted garage where you could get "expert" opinion with them being present to try to identify your problem? They shouldn't charge for it.

[steve2006]

I'm not over familiar with the later VVTI engines but with having new plugs fitted and it only being an issue at idle speed could there be a problem with the IACV as this contols the airflow only at idle.

I know there have been problems with this on the earlier moldels and assume the VVTI version uses a similar set up.

[The-Acre]

I'm not over familiar with the later VVTI engines but with having new plugs fitted and it only being an issue at idle speed could there be a problem with the IACV as this contols the airflow only at idle.

I know there have been problems with this on the earlier moldels and assume the VVTI version uses a similar set up.

I guess that's a real possibility, do you know how easy (or difficult) it is to clean? It really is only slight. I think most people wouldn't even know there's a problem, but when you've driven these cars for some time you just know something's not quite right.

Thanks also Dave for your input, if I don't manage to do it, or have time, I may just take it to the garage to get it looked at. If there's some sort of tutorial it would be useful.

Phil

[munday]

Worth cleaning the throttle body too, there is a guide on clublexus in the ls400 FAQ section :)

[The-Acre]

Worth cleaning the throttle body too, there is a guide on clublexus in the ls400 FAQ section :)

Thank you.