996 will not idle when cold - fixed, but why?

[farmer boy]

I have had a "cold" idle problem for some time (would not idle until engine warmed up a bit) and after messing about with various potential solutions I ended up changing the air filter for a new one and this cured the problem I am delighted that all is now well but I do not understand why! The old filter had done about 10,000 miles and although a bit grubby it was not so bad - I have seen much worse!

Any thoughts? I am wondering if maybe I have moved something else whilst replacing the air filter ..... anyway - just a thought. Any comment very welcome.

[Loren]

What is the model and model year of your car please (so we know if it is e-gas or not)?

[wvicary]

Possible MAF sensor reading low?

[logray]

On a cold start idle, how much does MAF really play into the running of the engine though wvicary?

[wvicary]

On a cold start idle, how much does MAF really play into the running of the engine though wvicary?

Actually not much at all that I know of from my readings and understanding of things.... I was just kinda guessing. The air filter replacement might just have been a coincident.

[Loren]

If it is a MY98 or 99 then it could be the ICV - which is why I asked model year.

[farmer boy]

Hi, its a 1998 996 C2. UK car... I had already "cleaned / checked" the MAF sensor and checked for leaks in the various vacuum circuits and cleaned some gunge from the butterfly... I actually gave the old airfilter a brush down to clean it up a bit and noticed a marginal improvement in the tickover - ie would run soon after start (not straight away) so I thought a new filter would be a good idea....... and she ticks over straight from cold now. I have noticed that the rpm drops quite low - (300 ish) immediately after start but then quickly rises to a steady 800rpm or so. Note that the throttle is not touched at any stage.... a bit of gas at startup and she ticks over at 800 ish straight away. I was wondering if I have inadvertently cured a leaky joint where the air intake joins the throttle housing (big jubilee clip holds it on) and that has cured the problem..... I find it difficult to accept that the airfilter was "strangling" the engine.

Anyway it is fixed now so I am happy ...

[farmer boy]

ps whats an ICV please?

[Loren]

ICV = Idle Control Valve

Your car has one and it is likely gummed up and/or not functioning properly.

You can try and clean it with fuel injector/carburetor cleaner but it may end up having to be replaced.

There is a vane inside the ICV that turns to allow different amount of air in at idle. This vane should turn freely. You can test off the car with a 12 VDC source to the solenoid.

I would start with a through cleaning of the valve (be careful with the paper gasket item 7 and it can be reused). While you are there clean the throttle body well including behind the butterfly.

If that does not work then you will likely need a new ICV (item 7).

[farmer boy]

Thankyou so much - a good clean was indeed required. You are a genius!

[Daniel-986]

It's not nessesary to open the ICV? I don't want to damage it, its a expensive part.

Edited November 4, 2011 by Daniel-986

[logray]

You can clean it without opening, but you have to remove it from the throttle body (careful not to damage the paper gasket, but it is cheap to replace if you do).

Some people have gone a "step further" and pressed out the pin and dismantled it to clean it, but I don't think that is necessary.

[Daniel-986]

I'd cleaned the TB today, and replaced the air filter. But I left the ICV with carbon, because this part is unknown for me. I dont wanted to get springs or such jumping in my face...you know what I mean...

Thanks for help, I think better to open the ICV to get the best cleaning result.

Man, the 996 accelerates fast, my Boxster is for sale now ;-) In Germany most Autobahn sections are without speed limit. Yipieeee.

[logray]

The IACV is operated by electromagnet. You can safely spray carburetor cleaner or equivalent inside the ICV and use a towel or rags to clean out.. Be sure that it drys completely before reinstalling. You really do not need to open it up to clean it well.

I remember driving on the German highways 10 years ago in a BMW 5 series, it was a lot of fun driving that fast and I miss it. I have heard though that the traffic gets bad. I will have to go back to Germany some day, but my German could use a refresher!

Last year in Italy and France was fun too. France has some great country roads.