1.8 GTi DX High Idle During Cold Start, 3,000 RPM

Hi all, Im asking this as a separate question from my other thread.

When starting, the engine runs on the WUR (assume) up to 3,000 RPM. Which is way too high for a cold engine? It creeps back down to normal idle RPM at +/- 1,000 RPM after about 1 minute, but Im worried that this initial start with cold oil and high revs could cause some long term damage.

So question:

What is the normal cold start engine idle speed?

What is the best way forward to fault find?

Thanks.

From cold mine ticks over at 1000 rpm, the same when hot.
Mine is a later car, 1988.

Sounds like the auxiliary air valve behind the inlet manifold or a split pipe going to it. It should have a wire connected and has a bi metalic strip that is heated up electrically as the car runs closing off the valve and keeping the idle stable as the engine warms up.
It does sound high rpm so I would check the pipework going to it closely as well. The extra air is tapped off the bellow just before the throttle body so this air is under vacuum in normal operation as well. If its pulling air from atmosphere its will be pulling a lot more.

Thanks guys - I checked the hoses to the AAV and there doesnt seem to be any issues. Will have to re-check again.

I also squeezed the AAV supply and it does slow the RPM down. I also believe there is a supply to the AAV. Not sure what this means at the moment?

OK - so a bit of an update. Took the car to a garage, had them look at it. Turns out the problem was the mixture was to lean, so when the car was on the WUR a big gush of fuel and away it went, hence the high idle speed. Mixture was adjusted up, timed up and the engine is now running well.

Cold idle is around 1,200 rpm, dropping to 1,000 rpm when warm. My next problem is that we cannot get the idle speed any lower than 1,000 rpm and so I suggest there is an air leak somewhere - possible around the throttle body. Its had a new gasket but still the same - spraying brake cleaner around the throttle body you can here a slight change in engine pitch.

With the idle speed not at the suggested 850 rpm, the fuel mixture is a little out still as I believe CO should be 1.8% @ +/- 850 rpm.

Still investigating…

850 is a bit low, I run mine at 950rpm and it seems happier at that speed.
Have a look at the idle adjusting screw, sometimes the rubber O ring breaks down and lets air past, it's at he back of the throttle body.

What type of fuel did they set the timing for?
You are best getting them set up for super unleaded (timing by the book) for normal unleaded they would of retarded the ignition. Changing the timing also affects the tick over.

Thanks Mark. I assume you mean the idle screw which is the brass screw on the rear of the throttle body?

We did have a conversation about super unleaded (which I now run on), and he did say that he had to advance the timing just slightly, so sounds like he has taken this into account.

Thanks for the help!

JS3 said

Thanks Mark. I assume you mean the idle screw which is the brass screw on the rear of the throttle body?

Yep that's the one, you should be able to unscrew it out and have a look at the O ring.