Poor runnning at idle, especially when cold
#1
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Poor runnning at idle, especially when cold
All,
My 88 S4 took a turn for the worse recently. At cold idle, it would run pretty rough and stall. As it warms up, it gets better but still never great. It's acting like it's running rich, except that there is no black smoke.
On start up and when cold, I would expect the idle to be at 1000 RPM or more, but this car seems to idle pretty low.
Any ideas on where to start in trouble shooting this?
Thanks
Al
My 88 S4 took a turn for the worse recently. At cold idle, it would run pretty rough and stall. As it warms up, it gets better but still never great. It's acting like it's running rich, except that there is no black smoke.
On start up and when cold, I would expect the idle to be at 1000 RPM or more, but this car seems to idle pretty low.
Any ideas on where to start in trouble shooting this?
Thanks
Al
#3
Team Owner
has this car ever has an intake refresh?
If not then it might be time to do this job.
NOTE simply fixing a few parts when there are many worn parts will only cause some of the other worn parts to fail later so you will be chasing your tail.
So for starters
Temp 2 sensor test it and or replace it.
MAF rebuild it
O2 sensor replace it
Coil wires replace them, as well as plug wires.
ISV spray down with WD40
NOTE
An intake refresh will include these parts^^^^ as well as,
both knock sensors,
the CPS,
the flappy pod,
the ISV,
the hall sensor fresh timing belt /WP
PC intake and cam covers,
new intake gaskets
fresh injectors,
new fuel lines,
new fuel pump check valve,
new dampers and FPR
new vacuum and vapor hoses
If not then it might be time to do this job.
NOTE simply fixing a few parts when there are many worn parts will only cause some of the other worn parts to fail later so you will be chasing your tail.
So for starters
Temp 2 sensor test it and or replace it.
MAF rebuild it
O2 sensor replace it
Coil wires replace them, as well as plug wires.
ISV spray down with WD40
NOTE
An intake refresh will include these parts^^^^ as well as,
both knock sensors,
the CPS,
the flappy pod,
the ISV,
the hall sensor fresh timing belt /WP
PC intake and cam covers,
new intake gaskets
fresh injectors,
new fuel lines,
new fuel pump check valve,
new dampers and FPR
new vacuum and vapor hoses
#4
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Thank you gentlemen, I'll look at what's required to replace / test these components. I recently went back to a stock exhaust system from an aftermarket noisy system. I bought the system used but externally, it looked good. I wonder of this has anything to do with it.
#5
Team Owner
might the O2 sensor wires have been damaged removing the cats?
#7
Nordschleife Master
All,
My 88 S4 took a turn for the worse recently. At cold idle, it would run pretty rough and stall. As it warms up, it gets better but still never great. It's acting like it's running rich, except that there is no black smoke.
On start up and when cold, I would expect the idle to be at 1000 RPM or more, but this car seems to idle pretty low.
Any ideas on where to start in trouble shooting this?
Thanks
Al
My 88 S4 took a turn for the worse recently. At cold idle, it would run pretty rough and stall. As it warms up, it gets better but still never great. It's acting like it's running rich, except that there is no black smoke.
On start up and when cold, I would expect the idle to be at 1000 RPM or more, but this car seems to idle pretty low.
Any ideas on where to start in trouble shooting this?
Thanks
Al
I had the exact same issue. Very rough cold starts - had to double foot it in my auto to get her out of the garage. After driving for 5 minutes and warmed, she ran fine, but not great. Was my Temp II Sensor wire connections to the sensor. The rubber boot was falling apart and my PO attempted some creative repair. When I stripped it down the wires were frayed, green, and barely making contact. Called Roger and got new connector hardware for a few dollars. Did my quality connecting work and looks and runs as good as new. My Temp II Sensor resistances on testing showed the sensor to be fine. Had an ISV/idle issue down the line, replaced (along with other intake refresh work), and now she purrs hot or cold.
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#9
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What plugs do these cars take, Resistor or Non Resistor?
I put NGK BP6ES in my other Euro cars and they seem to like them.
#10
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Al,
I had the exact same issue. Very rough cold starts - had to double foot it in my auto to get her out of the garage. After driving for 5 minutes and warmed, she ran fine, but not great. Was my Temp II Sensor wire connections to the sensor. The rubber boot was falling apart and my PO attempted some creative repair. When I stripped it down the wires were frayed, green, and barely making contact. Called Roger and got new connector hardware for a few dollars. Did my quality connecting work and looks and runs as good as new. My Temp II Sensor resistances on testing showed the sensor to be fine. Had an ISV/idle issue down the line, replaced (along with other intake refresh work), and now she purrs hot or cold.
I had the exact same issue. Very rough cold starts - had to double foot it in my auto to get her out of the garage. After driving for 5 minutes and warmed, she ran fine, but not great. Was my Temp II Sensor wire connections to the sensor. The rubber boot was falling apart and my PO attempted some creative repair. When I stripped it down the wires were frayed, green, and barely making contact. Called Roger and got new connector hardware for a few dollars. Did my quality connecting work and looks and runs as good as new. My Temp II Sensor resistances on testing showed the sensor to be fine. Had an ISV/idle issue down the line, replaced (along with other intake refresh work), and now she purrs hot or cold.
#11
Nordschleife Master
#2 is the Temp II Sensor. If connections/wiring looks good, then probably OK. Can confirm this by checking the resistances according to the WSM.
http://www.2010.cannell.co.uk/manual...s_porsche.html
I would next consider the ISV if you've kept the car in order (ie ignition cables etc... those mentioned by Stan).
http://www.2010.cannell.co.uk/manual...s_porsche.html
I would next consider the ISV if you've kept the car in order (ie ignition cables etc... those mentioned by Stan).
#12
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The ISV controls idle speed, but a car that runs poorly .and. idles poorly has something else first. Was there a backfire into the intake in the car's recent past? If so, look for a split vent or vapor hose under the intake. If a fuel regulator or damper is leaking, that's a possibility.
Of course, start off by bringing any maintenance items current. Looking specifically at ignition bits, the caps, rotors and wires are pretty much all-in well before 100k, for instance. The original plugs are WR7DC Bosch, superseded now by WR7DC+. NGK BPR6ES is probably the only substitute I'd consider in desperation. Fall not into the psycho logical trap of thinking that a more expensive platinum or multi-electrode plug must be better. Look at the old plugs to ID a cylinder that's irregular.
Do a simple 'listen' test with a stethoscope if you suspect injector wiring. Use a noid light to confirm findings.
I'm on the verge of putting together a travelling "care package" that would include the plumbing-parts intake tester, a noid light, a MitiVac or similar, a fuel pressure gauge, a cheap Ohm meter for plug leads. Maybe throw in a set of new plugs, and a compression gauge. And an instruction manual.
Of course, start off by bringing any maintenance items current. Looking specifically at ignition bits, the caps, rotors and wires are pretty much all-in well before 100k, for instance. The original plugs are WR7DC Bosch, superseded now by WR7DC+. NGK BPR6ES is probably the only substitute I'd consider in desperation. Fall not into the psycho logical trap of thinking that a more expensive platinum or multi-electrode plug must be better. Look at the old plugs to ID a cylinder that's irregular.
Do a simple 'listen' test with a stethoscope if you suspect injector wiring. Use a noid light to confirm findings.
I'm on the verge of putting together a travelling "care package" that would include the plumbing-parts intake tester, a noid light, a MitiVac or similar, a fuel pressure gauge, a cheap Ohm meter for plug leads. Maybe throw in a set of new plugs, and a compression gauge. And an instruction manual.
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Thanks, where is the ISV? The car has not back fired and the wires are all news. On MB the resistance is in the wires so non resistor plugs are recommended. Can I use NGK BP6ES instead of the resistor plugs?
The only recent change are
1) Stock muffler (used) was installed in place of the big bore system
2) New battery
I did notice that the car runs better without an air cleaner but the air filter is new.
Many thanks
The only recent change are
1) Stock muffler (used) was installed in place of the big bore system
2) New battery
I did notice that the car runs better without an air cleaner but the air filter is new.
Many thanks
#14
Nordschleife Master
The ISV sits atop the throttle plenum. It is the piece held by those two bolts in the center of the plenum. You have to remove the manifold to get to it. Here's a pic from the famous Dwayne. See his site to for various projects, and use his images to help you with whatever you do. I keep his site bookmarked.
http://dwaynesgarage.norcal928.org/
http://dwaynesgarage.norcal928.org/
#15
Under the Lift
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Who's recommending non-resistor plugs? Porsche calls for resistor plugs, not that I think it will matter much. Non-resistor plugs are not going to make the car run any better.