Increasingly annoying warm idle issue-CIS

[911SauCy]

Alright, we'll start with the only change I've made to the fuel system since this has become more prevalent is changed the fuel pump last month.

The car had done this last year a few times after good long rides on the highway, get off, push in the clutch and about 50% of the time, the idle would stay high, usually between 1300-1700. Around town it was much less infrequent and would almost always drop back to the normal 850-900rpm idle.

I've only driven the car 3 times this year/since new FP, and this is occurring more frequently, in/around town driving as well, and getting off the highway a few times the idle wouldn't dip below 2000rpm today and only about 30% of the time would it drop down to the normal idle rpm.

My thoughts in no particular order:
-new pump = higher pressure which is magnifying a potential issue in the CIS?
-throttle cable getting hung-up somewhere?
-no idea so I'll stop suggesting things and listen....

I appreciate any input.

Sean

[kodioneill]

Year/model ?

[schumicat]

check the aux air regulator is opening when engine cold and closing when hot. spray some wd40 to keep it from sticking. do some searches and you can find procedures. it is very simple and only takes a minute.

[Joe Bob]

Most cases of idle fluctuation is an intake leak. If an SC could also be a cracked air box.

Carrera and 3.6 models a worn out 02 sensor could be an issue.

[mdripley]

my 87 930 did this it turned out to be the red fuel pump relays in the front boot

[Paulporsche]

I see you have a 78SC.

Try plugging the line to the top of the decel valve and see if that helps. The valve regulates how often the revs stay up between shifts or after being @ a high rev. These can go out of spec but can be adjusted via the nut @ the top.

This is provided you have the older style valve located to the driver's side of the engine.

If there is no change, I would start looking for vacuum leaks, as was suggested.

[911SauCy]

Thank you guys.

I will take these few things into consideration as I do not think its a vacuum leak, it may be but I don't think so. Reason being is car warms up properly and idles, when I remove oil cap the idle lowers then goes up when replaced. I will search if other suggestions don't seem to help.

[911SauCy]

Originally Posted by kodioneill

year/model ?

'78sc

[911SauCy]

Originally Posted by schumicat

check the aux air regulator is opening when engine cold and closing when hot. spray some wd40 to keep it from sticking. do some searches and you can find procedures. it is very simple and only takes a minute.

Sprayed a little wd-40 on the little shaft on outside and little inside hoping to lubricate the "trap-door".

I'll let you guys know results of this.

S

[911SauCy]

Originally Posted by Paulporsche

I see you have a 78SC.

Try plugging the line to the top of the decel valve and see if that helps. The valve regulates how often the revs stay up between shifts or after being @ a high rev. These can go out of spec but can be adjusted via the nut @ the top.

This is provided you have the older style valve located to the driver's side of the engine.

If there is no change, I would start looking for vacuum leaks, as was suggested.

This is next on the fix list if wd-40 doesn't seem to do the trick on the aux air.

[911SauCy]

So after responses here and reading a number of tricks for the decel valve I took the wife for a ride

As shown in the picture the vac-line on the top of the decel valve has a piece of something metallic already blocking it....it's apparently been blocked since I've gotten the car.

I did lube the AAV with wd-40 before leaving, in the tube and the small hole above where it says "Bosch"...which I believe is the arm the "guillotine" like door is affixed to.

FINDINGS: Car was acting overall, remarkably better. Almost always dropping down to idle, which I believe is actually set @1100...it kept going directly to 1100rpm. (I'll adjust that once this is in the bag

REPLICATION: Hopefully this is important. Basically without fail was able to replicate the 1850-2000rpm idle with long, high rpm, deceleration runs. A few on exit ramps and one down a long hill. Once this became more evident coming off the highway I just tossed it in neutral, it dropped to 1100. Then said, "wife watch this " and kicked the revs, and tossed it in 3rd with rpm's @ 4k. Get to the bottom of the ramp, push in the clutch....we're at 1900.

Thoughts, please gentlemen.

Also...saw a gorgeous Guards Red 930 on I-84W in Southington...SauCy Saw Ya!

[Paulporsche]

Try unplugging the line and reconnecting it to the valve. Set the idle speed down to 950 w/ the wide adjustment screw.

If you can verify that all ignition components are good, no vac leaks, and timing is good then it might be time to move on to fuel and control pressures and mixture (CO%).

[911SauCy]

Originally Posted by Paulporsche

Try unplugging the line and reconnecting it to the valve. Set the idle speed down to 950 w/ the wide adjustment screw.

If you can verify that all ignition components are good, no vac leaks, and timing is good then it might be time to move on to fuel and control pressures and mixture (CO%).

Paul,

After I unplugged the line and found this, I put it back on. That's when everything seemed to work better together, minus the high rpm deceleration/issue replication situation.

After replacing the cap/rotor/wires, I did have a well known shop here in CT perform a complete tune-up last season. The car has been performing awesome and consistent since then...aside from this new little gremlin.

I'll have time tomorrow evening to spray around for vac leaks.

[Paulporsche]

Good.

Make sure your throttle cable and linkage aren't hanging up anywhere.

Do you know how to turn your idle speed down?

[911SauCy]

Originally Posted by Paulporsche

Good.

Make sure your throttle cable and linkage aren't hanging up anywhere.

Do you know how to turn your idle speed down?

The throttle cable thing was also something in the back of my mind.

I have not turned the idle speed down before, but I'm sure I can figure it out.

[NoYouRelax]

I am fighting major idle issues too and I do not seem to have any air leaks. I found great improvement when I disconnected my O2 sensor, but the gas mileage is not so good. I was also advised to try some Techron in my fuel tank. That seemed to help too, but be prepared to change out your fuel filter as the Techron is affective in move fuel crud/sludeg through your fuel system. I think my fuel distributor plunger might be hanging up some. Maybe others can weigh in on this?

Did you confirm good operation of your WUR? I also just bought a CIS pressure test kit to map things out further.....the saga continues.

[911SauCy]

The WUR checked out less than a year ago, not saying it couldn't be the issue however.

Other than reading stuff here, wouldn't know how to just dive into the WUR. But I'm not thinking that's the issue as I have narrowed almost all symptoms being caused by a high rpm deceleration run.

There are no other instances of the car acting strange while running, not lean/fat, surging etc

I do have a little black carbon build-up on the bottom of the bumper but I assumed that's caused by the Fabspeed Euro Pre-Muffler and muffler delete combo I run.

[NoYouRelax]

Pressure test kit helps prove out the WUR, but I had a loaner WUR that did not help matters. Have you tried Techron in your tank? Have you check the pop off valve? That can be a tough air leak to detect so I was advised to confirm its seal with a bead of vaseline on the seal under the flap.

[911SauCy]

Originally Posted by NoYouRelax

Pressure test kit helps prove out the WUR, but I had a loaner WUR that did not help matters. Have you tried Techron in your tank? Have you check the pop off valve? That can be a tough air leak to detect so I was advised to confirm its seal with a bead of vaseline on the seal under the flap.

Have tried Techron and will definitely try the Vaseline...