911SC - hot start, rough idle problem

[SCWDP911]

1983SC with stock 3.0 and CIS, top end rebuild 20k ago, new plug wires 3 months ago, 140k total miles:

Well, I have searched around on this topic and seems the other related threads were all hard to start and rough idle. Mine seems to be slightly different problem, as it starts right up, but then is rough idle...

Went on a 1000 mile weekend trip out to the Porsche Palooza. There was plenty of spirited driving along the way and while there. Coming home yesterday, we left around 9am and drove about 45 miles and stopped to gas up. After filling up with gas, turned key, car fired right up, but was idling low and rough (very lopey)... around 300-500 rpm. If I did not help it with a little gas, it would die. She would run fine while giving her gas. So I nurse it out of the gas station and drive down the road maybe a half mile, and then it seemed to be fine after that when I would come to a stop where it would idle again at about 900-950. Drive another 150 miles or so, stop for a break. Start up again and same exact thing as last stop. Outside ambient temps on t he drive home was low 70's.

Got home last night and parked in garage, I have not gone out yet this morning to start it up. After reading some on here, it makes me wonder about the fuel pump check valve, but I want to make sure before I start replacing parts. Any other things I should check or eliminate before buying a set of CIS gages?

Thanks

[Nostril Cheese]

maybe fuel accumulator as well?

[boyt911sc]

[QUOTE= Any other things I should check or eliminate before buying a set of CIS gages?
Thanks[/QUOTE]

V8,

If you're planning to do your own CIS troubleshooting effectively, borrow or buy a CIS fuel injection gauge kit. You'll be saving time and money utilizing this tool in your quests to locate questionable CIS components. For $75 or less, a nice kit could be purchased.

Without this kit, you'll just be guessing which CIS part/s to replace. Just my two-cents.

Tony

[SCWDP911]

Tony,

I hear you. I have been looking around for a set, but honestly, wondering which one to purchase. The local autoparts store sells fuel injection pressure test gage kits, are these OK to use, or are there actually CIS specific kits on the market I should be looking at.

I just mostly wondered if I should check anything else before completely diving into my CIS?

Thanks

[jtfreels]

Ok this is getting weird!
Made the same trip as Shane this weekend, first he complains about his seats, I had the same complaint.
Now this, I noticed the same symptoms, rough idle after a brief warm up. Same thing this morning, was fine till the car warmed up then dropped to about 900 and rough.
Altitude change? We went from 280 above sea level, up to 2000 feet, then back down again.
Which would be odd since my car is a Denver car and I've made no changes to the CIS since bringing it from there to Memphis a year ago.

Jay

[SCWDP911]

Jay, is yours staying rough after it gets warm? Mine seems to get back to normal after I drive it a little bit, maybe a mile at the most, and if I stop, it is still fine, idling where it should be. But if I shut her down, and then restart, that is when I see the idle speed drop and get real rough...

Funny though, I too was wondering about the change in altitude... I guess I need to go start her up and and see how she is acting today...

BTW, I hope you took Hwy 7 south to Russellville!

[Paulporsche]

V8,

Time to search Souk and jim williams. They both have lots of CIS info and tips. This type of CIS behavior happens often this time of year as temps fall. A CIS fuel gauge will help your diagnosis.

Quite likely your cold control pressure is too high resulting in a too lean condition during warmup. This is often caused by an out of spec WUR. You should also check the AAR. It's also possible your mixture is simply too lean, or you have vacuum leaks. Do you have a functioning airbox popoff valve?

JC Whitney has the CIS specific gauge for $60.

J,

Are you overdue for a tuneup? Wires, plugs rotor, etc? How about fuel filter? Injectors and boots?
You could also try raising your idle speed a little and see if it smooths out.

[KNS]

Altitude shouldn't be a problem, I regularly drive from 1500 ft to 5500 ft and back without any trouble...

[jtfreels]

Shane,

My problem seems to be when warm, after 2 hours running on the interstate yesterday pulled off and as it dropped to idle dropped below 1000rpm and was rough. I've not gotten the car real warm today but still a low idle.
We went all the way down 65 to I40 got home about 4:30PM, Jerry and Lynn went back down 23. My wife just wasn't up to the twisties Sunday

Paul, I've done about half what you suggest, but I am due for rotor and cap. Odd thing about this is it just happened all at once.

I'm wondering could it be Arkansas gas? Shane and I both filled up twice in Arkansas, first tank at the same place, second time at different places. I didn't check to see if I was getting any corn squeezings in the fuel.

Jay

[SCWDP911]

Originally Posted by jtfreels

Shane,

My problem seems to be when warm, after 2 hours running on the interstate yesterday pulled off and as it dropped to idle dropped below 1000rpm and was rough. I've not gotten the car real warm today but still a low idle.
We went all the way down 65 to I40 got home about 4:30PM, Jerry and Lynn went back down 23. My wife just wasn't up to the twisties Sunday

Paul, I've done about half what you suggest, but I am due for rotor and cap. Odd thing about this is it just happened all at once.

I'm wondering could it be Arkansas gas? Shane and I both filled up twice in Arkansas, first tank at the same place, second time at different places. I didn't check to see if I was getting any corn squeezings in the fuel.

Jay

Man, I hope I didn't get any corn squeezings in there!

I just got back in from taking my daughter to her flute lesson. Drove the car around a while while waiting. Went and washed off all the Arkansas November bugs from the front of the car (engine off at this point). Restarted car, and rough idle again. Drove it around a bit and seemed to be a little better again, pulled over and it seemed to be idling OK, but only at 750 (after driving for 20 minutes)... I bumped the idle up again to 950 and picked daughter up. Seemed to be fine the rest of the trip. It is kind of weird that we both are having possibly the same problem, after going to the same area, and buying gas from the same place at least once...

I think someone suggested earlier about running this gas out of the car and getting some "good" gas back in and a bottle of techron. Maybe that is worth a try until I get my CIS test kit here. Jay, I am probably going to order a set tonight, so if you ever need to borrow...

[jtfreels]

Yeah, I'm going to run the gas out before messing about with it too much. Gas is the only thing that has changed since Friday morning!

Check out this thread

Ballpark adjustment of CIS idle mix

[mark '87 930]

Old thread... but V8.. did you fix your problem? My car has started to do the same thing. If I adjust my idle for when it idles loq and rough.. it'll be set way to high for the next day's cold start...

so,I wondering if you found anything?

[SCWDP911]

Well, my problem is gone, but I can only tell you my best guess as to the solution for my situation.

Jay Freels and I had gotten gas at the same gas station I believe there is Arkansas on our way home from Porsche Palooza last November. We both had similar running conditions after that fill up.

I ran the a few more tanks through with some Berrymans and it eventually stopped occurring, maybe after the second tank refill after the trip.

Sorry I have nothing else to add really. This is the only thing that made sense at the time, as far as what had possibly changed, what was common with Jay's car, and what seemed to eventually clear it up. Hope it helps you.