My car doesn't always idle evenly. Usually when I start the car it stays right at 1000. However, sometimes after driving for a while it will go up and down in a regular pattern, fluctuating from 500-1000rpm. Doesn't seem to matter if the engine is just slightly warmed up or very warmed up. This doesn't happen ALL of the time though- I'd say a bit more then 50% of the time. The rest of the time it just stays at 1000 and doesn't move.

The only thing that comes to mind (mostly because I'm still learning about engines) is that maybe it's an injector(s), but if that was the case I'm not sure what would cause it to be so inconsistent.

I have had some problems with lower then optimum voltages at the battery, would this cause it to drop like that? I haven't taken voltage measurements at the different idle states- maybe that's the next thing to try to see if they're related?


If it was a vacuum leak I'd have a higher then normal idle, right?

I used the Search function and came up with two pages of stuff that might be interesting for you.

First of all, you are not alone - my 1.7 with FI is exactly the same.
Second, I was told the answer - Dr. Brad914.com had listened to my car for approx 3.2 seconds at idle as a pulled up to the driveway and offered his seasoned advice "you are running lean. the idle is 'hunting' - it is about to go too low and die then it kicks back in and goes a bit too high and repeats." Rather that seek the answer from the Guru himself, I started asking about other things on my car....

So, I am hoping that others will contribute and maybe confirm this "lean" thing. I am a little worried that my head/oil temps might be higher thatn they should be because I am running lean. However, I don't know at exactly what rpm range it is really a problem, and overall, it runs like a champ!

I forget about the search tool every now and then.. Maybe because sometimes I just get a message that it can't find any topics containing the word(s) I'm searching for. I'll give it another spin though...

did you notice that the word "search" was also a link? click on it

lean at idle

check those rubber fabric covered intake runner seal thingies--they crack and with the german stuff, you'll never know.

You definately have a vaccuum leak.

Carb cleaner or better yet that compressed air in a can stuff will work wonders finding the leak. That compressed air stuff is actually a refridgerant, and engines dont take kindly to burning soemthing that wont burn

Use the force Luke!

Teach us yoda
But seriously, I have a can of compressed air that I use to blow crumbs deep into my keboard and I'd rather use it as an excuse to head to the garage and tinker on the 914!

So I get the engine running - it is now hunting for idle - and I spray the air on all the hoses and hose joints. Start at MPS then finish at injectors? Start at fuel filter? Spray air into air filter?

Carb cleaner is an engine fire waiting to happen. Shoot some water out of a spray bottle, With vacuum Leaks your Ears are your best friend and your listening to hear the liquid getting sucked in. Vacuum leaks are soooo common around the Heads where the manifolds bolt down and where your boots clamp.

wouldn't using water to look for vacuum leaks be bad? If water gets sucked into the fuel lines that seems bad. Carb cleaner is very toxic and caustic, but would burn clean....still waiting on the compressed air trick.

I did read through lots of the search results and got a lot of junk...maybe it is time to consult Haynes...or McMark this weekend. No rush cause I'm usually running great just doin the hunting idle thing 30-50% of the time, the other 99% of the time my foot is firmly planted on the gas!

Yes, vacuum leaks are usually at the:
plenum to runner gaskets
runner to manifold gaskets
injector to manifold o rings
AAR valve hoses

This is another specific good article to read. Comes directly from one of the FI masters...

That would be an interesting senario, I'm trying to picture exactly how the water would make it into the fuel lines when looking for a vacuum leak at the heads and the intake manifolds. I did suggest using a spray bottle, Not a power washer. Are we both talking about a gasoline combustion engine?

I chuckled at that too... Misting water is not going to get sucked into the fuel lines.


Hey Robert, drive it over. I bet we can solve this pretty quick. At worst we learn a little and enjoy a visit.

its not compressed AIR, but compressed refridgerant.

vac leak sucks that in and idle drops some.

b

Thanks for the offer Rand! Much appreciated I might have a little time this weekend, but we're trying to get the house painted before the wife and I leave for a 2 week vacation. I'd love to make that happen (would be fun to check out your music setup too!). What's your schedule like?

I'll PM you.