the gremlin hiding in my engine bay

[flatsixturbo]

Hi, my Carrera has a minor issue, and I am in need of some veteran advice. I own an 88 with 102k on the clock. It runs well and exhibits no problems other than what is outlined below. Upon cold start, the car does not settle at a normal cold idle, but tries to drop immediately to 600-700 rpm. As you can imagine, it struggles a bit to maintain that. On occassion, it will pop to 1200 rpm or so for a moment, at which speed it is smooth and unstresed, before again trying to idle at 700. Additionally, once the car is warm, it will idle 500-600, which I believe is still about 200-300 rpm below where it should be. Whether hot of cold, once off idle, the flat six pulls smooth and strong and responds well. Of final note, the car may also a exhibit a gentle surging during part-throttle acceleration between 2000rpm and 3000rpm, but it so slight that I may just be paranoid, or unrelated. Thanks in advance for any advice you can give
Dan

[Peter Bull]

It might be a faulty engine temperature sender, or the wire to it.

/Peter

[tcar]

Is it a 930? You don't say... but from your name it looks like it.

[flatsixturbo]

Temp sender. Okay, I'll keep you posted. Thanks for the suggestion

[flatsixturbo]

My car is an 88 Carrera

[stlrj]

I would start by having my mixture checked and adjusted to spec. before replacing parts that are perfectly good.

[flatsixturbo]

Sounds great, thanks. I'm a big fan of not spending money that doesn't need to be spent.

Sorry for the confusion. My car is a 1988 911 Carrera. The 930 only carried both "Carrera" and "Turbo" designations in '75 and '76. So by saying that my car was a Carrera, and metioning the year (88), I assumed I had made it clear. Again, I apologize for the confusion. Although this may have something to do with the mixture suggestion, because I was under the assumption that the Motronic management system set the fuel ratios electronically and therefor could not be adjusted. But if everyone was assuming that my car was a 930 because of my screenname, then I would understand the suggestion to adjust the (CIS) intermix ratio.

[zbph10]

Have you checked the O2 sensor?

[stlrj]

Mixture on the Motronic is adjustable and very specific.

[Wayne 962]

I hate troubleshooting problems on these early Motronic systems - there are no computers that give you trouble codes. Start with the easiest thing - check for vacuum leaks...

-Wayne

[flatsixturbo]

Great, thanks for the info, guys. i'll keep you posted

[Laneco]

Check for vacuum leaks - including the intake runners to the heads. When you are satisified that there are none, move to mixture check/adjustment.

After that, well, do whatever the other guys tell you - the first two items have been successful for me on a couple of these cars.

angela

[donporfi]

Check also the idle control valve.

[flatsixturbo]

I've never done a vacuum leak check before, If it's not too much trouble, could somebody outline the procedure for me? thanks

[flatsixturbo]

Oh, and no, I haven't checked the O2 sensor. By 'checked' do you mean replaced, or is there actually some way to test its function?

[DW SD]

Originally Posted by donporfi

Check also the idle control valve.

+1 - You can remove the ICV and plug the inlet line to which it is attached. Put it through the cold start routine and see if it exhibits the same behavior.

You can also try cleaning this device. I would use MAF cleaning spray or something compatible with electronic devices. carb or brake cleaner may cause issues.

Doug

[scarceller]

Originally Posted by flatsixturbo

I've never done a vacuum leak check before, If it's not too much trouble, could somebody outline the procedure for me? thanks

Get the car running and idling then simply spray starter fluid around all the intake parts. Be sure to spray down in the 6 areas where the intake runners attach to the heads. If you have a vacuum leak the RPMs will go up when you introduce the spray.

The much better way to find these is with a smoke machine, you could ask the local mechanics who has one. They don't charge much for this test, my local guy charges $40.00 and it's well worth the money.

[rick-l]

here is a thread on the idle air control.

3.2 idle control valve go bad

[flatsixturbo]

Got the starter fluid and MAF cleaner today, hope to get to them both this evening . . .

[DW SD]

Others have used brake cleaner, from review of the other thread 3.2 idle control valve go bad . You can always use brake first and then use the MAF cleaner to ensure the contacts are good.
MAF cleaner is definitely less harsh.

Did you review the procedure for setting the idle mixture? You can do this at the same time as the ICV is removed.
Steve Wong has it on the www.911chips.com website, I think.

Good luck!

Doug