Low, rough idle
03-14-2014, 04:53 PM
#61
Under the Lift
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Thread Starter
Karl: You and I are on the same page. I would expect SURGING idle with a vacuum leak. But other than the stable, high idle, the car runs terrific. Stan had a case where a stable, high idle proved to be a stuck ISV. Louis has my old MAF right now. Waiting for word and return of that.
03-14-2014, 05:52 PM
#62
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
My 88 is having the same high idle issue. Pretty much the same numbers you have. I just finished an intake refresh that included a new ISV, so I suspect it is not that, although sometimes that last thing you touched..... I think my next step is to blow some smoke into the intake manifold and look for air leaks, although I usually think of air leaks as making the idle drift and in this case the idle is very solid.
03-15-2014, 05:40 PM
#63
Under the Lift
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Thread Starter
The idle SHOULD adapt on it's own. I've never had an issue with idle until now. I've run the idle adaptation only occasionally but not after each battery disconnect.
Louis said my MAF was reading terribly low. A rebuilt MAF is on it's way to me now.
Louis said my MAF was reading terribly low. A rebuilt MAF is on it's way to me now.
03-19-2014, 07:00 PM
#64
Under the Lift
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Thread Starter
Problem solved. It was one failure - the MAF. I received a JDS Porsche rebuilt MAF from Louis Ott. He said my original was VERY weak. My symptoms were a low, rough idle and some problems above that. A borrowed MAF, which looks like it needs to go to Louis as well, caused the idle to be HIGH, although the car otherwise started and ran very well.
Popped the rebuilt MAF in after a battery reset, car had a low but surging idle initially after each start that would settle down to a lowish idle with some stumbling throttle response that smelled rich. Kind of expected that might happen with a new MAF. Drove about 20 miles and throttle response improved but the idle remained low but smooth with the same oscillation for short while after start up. Ran the idle adaptation with Theo's Porsche Diagnostic program - all better now. Idles at 650. Runs great, but not quite as responsive as the high idle MAF. Need to drive it more to let the LH do some tuning.
Anyway PROBLEM SOLVED. MAF's are strange animals that seem to have some variable failure modes.
Popped the rebuilt MAF in after a battery reset, car had a low but surging idle initially after each start that would settle down to a lowish idle with some stumbling throttle response that smelled rich. Kind of expected that might happen with a new MAF. Drove about 20 miles and throttle response improved but the idle remained low but smooth with the same oscillation for short while after start up. Ran the idle adaptation with Theo's Porsche Diagnostic program - all better now. Idles at 650. Runs great, but not quite as responsive as the high idle MAF. Need to drive it more to let the LH do some tuning.
Anyway PROBLEM SOLVED. MAF's are strange animals that seem to have some variable failure modes.
03-19-2014, 07:55 PM
#65
Official Bay Area Patriot
Fuse 24 Assassin
Rennlist Member
Fuse 24 Assassin
Rennlist Member
I agree about the various failures. Remember all my idle trouble? Despite it NOT being the MAF and the wiring harness, mine did some weird stuff too that still sends a shiver up my spine.
03-19-2014, 08:41 PM
#66
Hi all,
As usual great diagnosis help and description of procedures undertaken in eliminating possible faults.
Stan great idea re the model brass tubing, a real bugger getting the inserts in. I have a full set of long screw drivers and a good "cree" head torch, but have difficulty standing on my head.
Bill, great feed back on what was done and hopefully similar feed back will migrate and energise some of the other members of the 928 community to do the same when problem solving.
Great result.
My 928 currently having a repaint job and spending time getting my 1990 944 turbo "S" running smoothly. There are lots of part similar on both cars.
As usual great diagnosis help and description of procedures undertaken in eliminating possible faults.
Stan great idea re the model brass tubing, a real bugger getting the inserts in. I have a full set of long screw drivers and a good "cree" head torch, but have difficulty standing on my head.
Bill, great feed back on what was done and hopefully similar feed back will migrate and energise some of the other members of the 928 community to do the same when problem solving.
Great result.
My 928 currently having a repaint job and spending time getting my 1990 944 turbo "S" running smoothly. There are lots of part similar on both cars.
