Fast Idle when warm
06-25-2009, 06:05 AM
#1
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Fast Idle when warm
Rob Aickin Brisbane Australia 79' auto 928 Idle runs up to 1600rpm after a few minutes..when warmed up.
Inherited car as non runner, have done water pump, timing belt and water bridge. Runs smooth at cold about 800rpm then runs away. Where should I start?
Inherited car as non runner, have done water pump, timing belt and water bridge. Runs smooth at cold about 800rpm then runs away. Where should I start?
06-25-2009, 11:35 AM
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Burning Brakes
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I would start with the Warm Up Regulater (WUR), squarish aluminum part, front of engine. It may be full of gunk, plugged up screen(s), poor vacuum. Next, Aux Air Valve, cylinder styled bit with air hoses in/out, pass side of throttle body, back of engine. Again, may be full of gunk, not closing on warmup. Finally, fuel distributor may be, you guessed it, full of gunk. You should also test\replace your temp sensors.
06-25-2009, 02:46 PM
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check the spider joints for air leaks.
__________________
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
06-25-2009, 02:59 PM
#4
Possible areas that will cause a high idle are a dirty or sticking air sensor plate, vacuum leaks or your throttle cable does not have enough slack in it. As mentioned earlier, the intake tubes are often overlooked as a souce of vacuum leaks, especially at the bottom of the rubber boots. Other areas that could cause a vacuum leak is the brake booster and decel valve (if equipped). Also, if you have AC, plug the lines to and from the idle solenoid as it could be leaking.
Dennis
Dennis
06-25-2009, 07:27 PM
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vACUUM LEAKS OR aux air valve - the latter more likely if it runs well. If it has False air from leaks it would not run well IMHO. Try crimping the hose that feeds the aux air valve when its warm and see if that lowers the idle, if so thats the culprit. The valve can be opened by drilling the rivets out, and replacing them with M6 bolts. More common failure mode is not giving enough extra air when cold to give a stable idle - BTDT. Check the bimetallic strip heater element is not broken, with a meter across the pins. If the internals are not completely broken, they can be adjusted - cool in freezer, adjust so its 80% ormore open, check that it closes as it comes back up to ambient.
Get a copy of Ben Watson on Bosch fuel injection, soft cover, Amazon, $15, invaluable for CIS cars.
jp 83 Euro S AT 52k
Get a copy of Ben Watson on Bosch fuel injection, soft cover, Amazon, $15, invaluable for CIS cars.
jp 83 Euro S AT 52k
