Idle issue
#1
Idle issue
Hi all
Looking for suggestions for the following problem.
I have an 88 S4 SE, fires up from cold absolutely fine, and idles perfectly for about 5 minutes, then shuts down as if you have turned the key to off, no rough idle, coughing or spluttering etc, however, if I set off driving after firing her up, there are no issues at all, until I pull up at a set of lights or a junction that is, at which point it can do one of three things, sometimes idles fine, sometimes the revs drop almost to the point where the car cuts out, but then recovers to idle normally, but more often than not, she just cuts out!
She can be started again straight away, at which point, normally idles ok after that, at least for a short period of time.
Oh, and to throw another symptom into the mix, sometimes idles high, all of these symptoms can be experienced in the one short trip.
Any suggestions on what to look at first would be gratefully received.
Cheers
Looking for suggestions for the following problem.
I have an 88 S4 SE, fires up from cold absolutely fine, and idles perfectly for about 5 minutes, then shuts down as if you have turned the key to off, no rough idle, coughing or spluttering etc, however, if I set off driving after firing her up, there are no issues at all, until I pull up at a set of lights or a junction that is, at which point it can do one of three things, sometimes idles fine, sometimes the revs drop almost to the point where the car cuts out, but then recovers to idle normally, but more often than not, she just cuts out!
She can be started again straight away, at which point, normally idles ok after that, at least for a short period of time.
Oh, and to throw another symptom into the mix, sometimes idles high, all of these symptoms can be experienced in the one short trip.
Any suggestions on what to look at first would be gratefully received.
Cheers
#2
The idle CO needs to be set correctly so that the idle loop adaptation can cope with all conditions.
Set it to 1-1.5% tailpipe with engine at working temperature.
If the problem still persists then it may be the ISV is sticking, a search of here can describe the way of squirting WD40 into it.
Another thing to check is idle vaccum, measured at the fuel damper at the front of the engine, there may be a leak. It should measure around 21"Hg.
Set it to 1-1.5% tailpipe with engine at working temperature.
If the problem still persists then it may be the ISV is sticking, a search of here can describe the way of squirting WD40 into it.
Another thing to check is idle vaccum, measured at the fuel damper at the front of the engine, there may be a leak. It should measure around 21"Hg.
#3
Looks like you had this problem a year ago based on previous posts. What's been done to the car since then?
Could be a bad idle control valve, vacuum leaks, or a bad Mass Air Flow Sensor (MAF) or combination of them. Should probably check all of that. MAFs should for the most part get rebuilt already so do that or buy one with a core trade.
Could be a bad idle control valve, vacuum leaks, or a bad Mass Air Flow Sensor (MAF) or combination of them. Should probably check all of that. MAFs should for the most part get rebuilt already so do that or buy one with a core trade.
#4
Hi all Looking for suggestions for the following problem. I have an 88 S4 SE, fires up from cold absolutely fine, and idles perfectly for about 5 minutes, then shuts down as if you have turned the key to off, no rough idle, coughing or spluttering etc, however, if I set off driving after firing her up, there are no issues at all, until I pull up at a set of lights or a junction that is, at which point it can do one of three things, sometimes idles fine, sometimes the revs drop almost to the point where the car cuts out, but then recovers to idle normally, but more often than not, she just cuts out! She can be started again straight away, at which point, normally idles ok after that, at least for a short period of time. Oh, and to throw another symptom into the mix, sometimes idles high, all of these symptoms can be experienced in the one short trip. Any suggestions on what to look at first would be gratefully received. Cheers
1988 s4 Auto ROW black/black West Australia
#6
Hi mate
Yes, in WA, I have been having my work done at Auto exclusive East Perth, they have done a fait bit of work on it now and I have been pleased with their work, the owner (Walter) races his Porsches, and does work for others involved in racing theirs, the premisies is pretty non-descript, but there is always some very impressive machinery in the workshop, he came highly recommended by another 928 owner in Perth, but always happy to recieve other leads to good mechanics closer to home.
Cheers
#7
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#8
The idle CO needs to be set correctly so that the idle loop adaptation can cope with all conditions.
Set it to 1-1.5% tailpipe with engine at working temperature.
If the problem still persists then it may be the ISV is sticking, a search of here can describe the way of squirting WD40 into it.
Another thing to check is idle vaccum, measured at the fuel damper at the front of the engine, there may be a leak. It should measure around 21"Hg.
Set it to 1-1.5% tailpipe with engine at working temperature.
If the problem still persists then it may be the ISV is sticking, a search of here can describe the way of squirting WD40 into it.
Another thing to check is idle vaccum, measured at the fuel damper at the front of the engine, there may be a leak. It should measure around 21"Hg.
Thanks for the info John, I'll check these out and let you know which one (if any of the above) is the culprit.
Cheers
#9
Looks like you had this problem a year ago based on previous posts. What's been done to the car since then?
Could be a bad idle control valve, vacuum leaks, or a bad Mass Air Flow Sensor (MAF) or combination of them. Should probably check all of that. MAFs should for the most part get rebuilt already so do that or buy one with a core trade.
Could be a bad idle control valve, vacuum leaks, or a bad Mass Air Flow Sensor (MAF) or combination of them. Should probably check all of that. MAFs should for the most part get rebuilt already so do that or buy one with a core trade.
Thanks again
#10
Hi mate Yes, in WA, I have been having my work done at Auto exclusive East Perth, they have done a fait bit of work on it now and I have been pleased with their work, the owner (Walter) races his Porsches, and does work for others involved in racing theirs, the premisies is pretty non-descript, but there is always some very impressive machinery in the workshop, he came highly recommended by another 928 owner in Perth, but always happy to recieve other leads to good mechanics closer to home. Cheers
1988 s4 Auto ROW black/black West Australia
#11
I use RPJ Motorsports in Briggs street Welshpool, hes been a porsche mechanic all his career, very smart guy on the 928's, we need to catch up and go cruising with Norm ( bogdann on these forums) 3 x 928 would look nice on the scarborough cafe strip.
1988 s4 Auto ROW black/black West Australia
1988 s4 Auto ROW black/black West Australia
I'll let you know when the idle issue has been resolved, more than happy to meet up anytime.
#13
Won't be a kick down relay as my car is a 5sp , but worth looking at CPS, I recently owned a Mercedes CL500 which is known to suffer from CPS issues, but according to the Mercedes mechanic, the cars can shut down at normal drving speeds, this has never happened with the 928, but worth checking al the same, cheers
#14
Make sure no one did troubleshooting and put a relay in the kickdown spot, it should be empty. My 87 acted wierd for years and it ends up I must have flipped pages or something because I has a standard #53 in there that was randomly shorting the tach signal to ground. It wouldn't happen until the car warmed up. Messed with the idle as well.
#15
This sounds exactly like a messed-up (aging or dead) narrow-band O2-sensor. When the coolant temp reached 50-60C then the LH starts adjusting fuel based on the o2-sensor reading. If the O2-sensor is providing bad info then the LH takes that bad info and does stupid things with fueling, as soon as the coolant reaches the magic temperature.
So if you have an O2-sensor (on top of the crossover just ahead of the cats) then try a new one. They typically last around 100km's, plus/minus.
Cheers, Jim