alabbasi

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

jpitman2

Idle stabilizer valve? Seems to be lots of queries on this. Do a search.
jp 83 Euro S AT 55k

Mrmerlin

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

alabbasi

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.

Mrmerlin

might the O2 sensor wires have been damaged removing the cats?

alabbasi

It was a cat back part of the system so the 02 sensor should not have been damaged. I'll put the car on the lift and take a look next weekend.

Thanks

MainePorsche

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.

FiveElements

How old are the spark plugs, wires and do all the sensors have good connections?

alabbasi

Thank you very much, lots of the wiring looks brittle on this car so i will inspect and report back

The plugs are old, but the car was not driven much since replacement (PO laid the car up about 7-8 years ago). Wires are brand new.

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.

alabbasi

Can anyone tell me which is the temp 2 sender. I tried testing the one in the front of the engine which appears to be the sensor to the temp gauge and the one on top of the intake. Both appear to be working , so I gave the contacts a good clean. It's still running rough, so bad that it will barely idle now. Kind of frustrating considering that it ran much better a couple of weeks ago.

MainePorsche

#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).

dr bob

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.

alabbasi

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

MainePorsche

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/

Bill Ball

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.