981/911

88 911 Carrera, 160,000 mi, daily driver. Runs great. Twice a week, in hot weather, when approaching a stop light, rpm will drop from 800 to 600. Sometimes it picks back up, occasionally it stalls. Starts right back up without problems. Doesnt do it in the winter. Replaced O2 sensor. Heat temp sensor was replaced approx 115,000mi ago. Any ideas? Thanks, Glenn

lfe132

I"ve been having a similar problem and it's costing a small fortune trying to figure it out. I keep replacing parts only to find out it wasn't the problem. Your problem could be a number of things; any where from a bad ground to a bad DME/ECU. Bad ground is easy to check, most likely at the engine intake runner; DME Relay is easy to replace and not to costly, after that your best options are: 1) find a friend with a similar car and start swapping parts or 2) take it in to a qualified Porsche mechanic; have them Dx the car and either have them fix it or at that point repair it yourself.
Good luck.

old man neri

What does the inside of your ICV look like, is it dirty? Might be worth the shot to clean it seeing as ti takes about 5 min and costs 0.35 in carb cleaner. I would do that and then go from there.

Once it idles does it idle properly?

dshepp806

Have you a Bentley manual to get some other measurements on various sensors?

Best,

Doyle

blomman

It runs rich! Set the co to about 2.5% and it will dissapear.

981/911

I will check the ICV valve today. Have the Bentley Manual to use as a reference. It doesn't happen very often and has been doing this for a few years, only in intense heat. How would I check and adj the co to 2.5 %? Yes, it does idle properly otherwise. Sorry it took so long, I was away. Glenn

981/911

ICV valve was dirty. Cleaned up the piston, it closes half way with power on like Bentley said it should but oscillates approx 2mm. while in the middle. Idle may be 1000 higher than it was. Will wait to see if it was the answer and let you know.

theiceman

i had that EXACT issue with my audi .. drowned it with wd40 untill black stopped coming out of it it has worked flawlessly fr years since.

981/911

Cleaned the ICV, followed the Bentley manual and checked and cleaned the air flow sensor. I think the A/C causes the RPM brief drop at idle. Blowman suggesting to make it run leaner was suggested to someone on a pelican discussion with the same problem. The Workshop manual says to connect a CO tester to the cat converter. Is the CO tester a resonable purchase in terms of expense? I have B&B exhaust and therefore no cat to connect to. The manual discusses bridging the test socket to stop the function of the idle volumetric control and turning the screw on the throttle body housing to adjust the idle. Could I just do this to bump the idle a touch without checking the CO first? Thanks

DRACO A5OG

Yes the LM1 CO Reader is Expensive. $400-$500.

Another way to do it is to Jumper the ICV and disconnect the O2 Sensor (leave in Cat, just disconnect the connection in the engine bay). Use a DVM on the O2 and get reading while car is on. Steve Wong, has a method of doing this. Search Pelican Thread on Chips. Then lean her out on the AFM. Reset Base Idle RPM's, 800 2K DMEs or 880 4K DME.

Once properly leaned, there will be no effect on idle when the AC turns on or Sub Dips.

Take Caution, you do not want to over lean her or you can damage the cylinders heads.

981/911

Could not find the Steve Wong post on pelican. Went through a 20 page search on chips at Pelican.

DRACO A5OG

Here you go Glenn:

Per Mr. Steve Wong:

If you're just trying to fine tune the idle mixture, you could do it by measuring the voltage off your O2 sensor. It switches right in the narrow band that you want to adjust it to:

http://forums.pelicanparts.com/showthread.php?t=104495 (POST #18, #25, #27 & #30)

Before doing this, check for intake air leaks that can cause some cylinders to run unevenly, causing low idle issues. Unplug the O2 sensor, and ICV plug, and spray engine starting fluid around all suspected points, espeically the intake manifold gaskets.

Beyond this, stock 84-86 Carreras just idle low, and can sub-dip on decel, as the engine and idle control valve ages, and use of the AC system. The only way to improve on this is to use software from the later 87-89 Carreras, which will raise your idle to about 880 rpm. Idle undershoot on decel can be cured with modified software which slows the rpm fall.

981/911

Drac, thanks for taking the time to help me. My pcar is a 1988 with an autothority chip for my B&B. Ran fine for several years with this chip. Car idles fine normally appox 800, it is only with high temps that I stall maybe once or twice per week during the summer. Don't know if it is the summer heat or that the air is on @ these times with an increase draw. Cleaned and checked the ICV valve and it did it once more. Cleaned the air flow sensor and no problem this week so far. Did run Steves check and got .25 which is actually lean. If it stalls again I think the next step would be to bypass the idle volumetric control @ the test socket and increase the idle to 880 with the control nut on the throttle housing. Sound correct?
Am curious about spraying starter fluid looking for a leak. Wouldnt that be a fire risk? Do you listen for a idle change to know that you found one?

Amber Gramps

use brake cleaner to find vacuum leaks. It will up your idle a bit. I had lots of leaks and use that cleaner with just abut every job I've done on the car.

DRACO A5OG

No Problem Brother must give Credit to Mr Steve Wong.

I would check the readings when it is hot, to insure it is not your O2 Sensor over compensating. But I suspect you are too lean causing Lean Sub Dips to Stall.

Sounds correct about the jumpering the ICV to adjust Base Idle, but set A/F ratio properly first.

'88 Carrera, your RPM is minimum 880 per Bentley, Steve and OEM Specs. 800 RPMs are for 84-86 OEM Chips. ( Remember the Tach reads from bottom 400, 600, 800 then 1000 RPMs, want to be just below middle of 800 and 1000 RPMs for the 880 mark )

I use Ethel, to check for leaks, no issue of ignition. Just dont spray over Known Open Wires, Plugs and Distributor for safety sake. Also feel around the front of the engine to insure you don't have any loose vacuum hoses, Ask me how I know :-)

Spray only on those usual 6 suspect points.

Break a Leg,

Jim