1987 911 engine idle high

[hangar21]

I bought a 1987 911 cab in colorado and drove to my home in texas. On start up, engine idles at 1400 rpm. After warm up, engine idle drops to slightly less than 1000 rpm. DME has the word "chip" written on the cover. Before I start spending tons of money replacing parts. I plan to have Steve Wong inspect & repair (re-chip) my DME, would the O2 sensor be a possible cause of the high engine idle?
Thanks,

Terry

[kanadary]

i don't know if this will help but on my 87 at start up its about 1100-1200 for a few second, atleast till i get to the first fourway stop then drops to 800 and stays there for the duration. i don't have an aftermarket chip or non stock exhaust

[hangar21]

Ken, Thanks for the info. my car has aftermarket exhaust that will be replaced at some point (really loud). The exhaust tips show evidence of a rich mixture, that's why I think the O2 sensor may be the problem.

Terry

[nesslar]

I would guess you might be able to simply adjust the idle at the ICV? I've jumpered per the "method" and gotten my (warm) idle up from about 750 to 850, no problem and it has held, always idles for "just a bit" at around 1150-12500 right at startup, then settles. I gotta believe your's is an easy fix.

[kidrock]

You say your idle drops to below 1K when warm....87-89 3.2 idle is 880 rpm at operating temp....sounds very close. If you want, you can jump B to C at the service port in the engine compartment while setting main idle screw....do this while engine is at operating temp.

If your engine seems "rich", you may want to take it to a smog specialist or someone with an LM1 exhaust reader. An adjustment to your air / fuel mixture can be made at your AFM box. A rich condition is usually a distinct smell at the exhaust, and a telltale sign of dark, sooty spark plugs.

Lastly, a bad O2 sensor is usually signified by a "hunting" idle (one that goes up and down and doesn't settle). Your motronic ECU is trying to compensate the air / fuel mixture from the crappy signal being sent by the bad O2.

[DRACO A5OG]

It basically sounds normal.

for '86-89, when cold at start up, it will run at 1200+ RPMS for 45 second then drop to 880 RPMs. (84-85 stock is 780 RPMs)

Make sure you are reading the tach correctly. remember there is no 0 or 200 RPM marks.

There are only 4 marks in the 1st stage of the tach, starts at 400, 600, 800 then 1000. 880 would be a hair less then the middle of 800 and 1000 RPM mark.

Remember never let is sit at idle, drive off immediately and keep it under 4000 RPMs the first 5 minutes as a minimum SOP, do not let it lug either.

+1 on kidrock, changing the O2S and starting the clock fresh isn't a bad idea.

[DRACO A5OG]

Originally Posted by nesslar

"Remember never let is sit at idle, drive off immediately..."
Sorry, I don't buy that for a second; never will. Nothing wrong with letting ANY car warm (or its oil) a little while......I do it, my car runs better than fine all the time........I do give it a little gas while it is sitting there burning the moisture out, of course.....
I think there are some old wives' tales regarding these cars that don't necessarily need to be perpetuated. Just IMHO........................with all due respect.

Well then PORSCHE MANUAL is telling HUGE "Old Wive's Tail". No feelings hurt here, I am not the one perpetuating the myth, and absolutely no dis-respect to you, but if you had read your car's owner manual you will clearly read PAG insists you "drive off immediately".

I believe others here that are more educated than me will advise why that is a fact and not just an opinion.

RSD!

[nesslar]

OK, cool. Sorry, no problem.

[hangar21]

Gentlemen,
I appreciate all the Intel concerning the idle and I did fail to mention that every now and again the idle does "hunt" when slowing to a stop, engine is at operating temperature.
My other car is a 1990 944, so this is my first "Air cooled" engine car.

Thanks again for the info. I'll let you guys know when I have the exhaust checked.

Terry

[dar636]

Originally Posted by nesslar

I would guess you might be able to simply adjust the idle at the ICV? I've jumpered per the "method" and gotten my (warm) idle up from about 750 to 850, no problem and it has held, always idles for "just a bit" at around 1150-12500 right at startup, then settles. I gotta believe your's is an easy fix.

+1, worked for me.

[kidrock]

Originally Posted by hangar21

Gentlemen,
I appreciate all the Intel concerning the idle and I did fail to mention that every now and again the idle does "hunt" when slowing to a stop, engine is at operating temperature.

Probably not the same kind of "hunting". If you're still concerned about a high idle, make the adjustment as we've outlined. If you still have an issue, it may be indicative of a small intake vacuum leak.