i am finally able to spend some time on the 928.. the house has gotten to a point that i can spend a few hours on the cars.


This afternoon i repaced the heater valve. After i was finished i checked the vac lines. all lines held vac.
My cruise works... sort of....

I set the speed and it starts to very slowly drift down... it will not accelerate from the cruise control...

If i keep a little weight on the pedal it will hold speed.. all i have to do is just touch the pedal and it holds...

any ideas?

 

Vacuum leaks, probably in the HVAC system.

 

makes sense... i have hvac leaks.....
can i bypass the hvac until i get the leaks fixed?

 

Yes, find the 5-way or 7-way splitter behind the MAF, take off the white vacuum line going to the HVAC (somewhere next to the A/C lines) and plug the splitter.

 

I believe it is a 4 way splitter on your 928 - connected to the power brake booster through a one way blue/black one way vacuum valve. You should buy a mity-vac and isolate the vacuum leaks. Unless your vacuum accumulator and vacuum actuator for the cruise control are leak free blocking off the HVAC line will not cure your problem 100%. Comb flap diaphragm in your HVAC system is the most likely leak source - you can confirm with the mity-vac. Wally Plumley has a write up on how to isolate HVAC vacuum leaks on the 928. You can find it on this forum.

 

On an 87 928 the vacuum line going to the HVAC is black and goes from the 4 way splitter into the firewall. The white line from the splitter goes to the flappy valve (air intake - not HVAC)

 

i have a mighty vac and used it, but did not find any leaks..was was not running however...
i left the vac on for 15 min and it went from 20 in down to 15... not much of a leak..

 

Repeat test with key on so HVAC is active. Not sure of best HVAC settings for this test. Maybe try several. Vacuum will likely drop when an actuator moves but should otherwise hold. Just pump it up between setting changes. Maybe this will point to particular diaphrams that are leaking.

 

Google Wally Plumly HVAC and you should find the instructions needed to find your HVAC leak. Remove the driver's side panel from the center console and you will see the 5 4mm plastic vacuum lines. Each controls a vacuum servo. You cut them with a sharp knife and test the line going up into the dash with the mityvac. Repair each cut with an tight fitting rubber hose connector. If you find a leak (won't hold vacuum) plug the end going into the control unit. A single leak can effect the entire system. No need to plug the line going into the dash. The orange line (comb flap) is the most likely culprit. Don't cut or test the black line - it is the vacuum supply from the brake booster.

Hope this helps.

 

Here is the web address: You don't need to take out the vacuum control unit in the dash - just cut each line, test, and splice with a tight fitting rubber connector.


http://members.rennlist.com/pirtle/svc_act.html

 

Any foreign car repair shop will have the rubber hose to repair your cuts. The plastic hoses are 4MM in diameter.

 

thxguys
i will look at it tomorrow.

 

did you look at it yet?
I have been searching CC problem threads, but fixes are seldom revieled.