User 121721

My car, when new, idled very smoothly with no rumbling or vibrations in the cockpit. Now, regardless of whether the car is warm or cold, it shakes/rumbles like a harley at idle. The dealer said that it was normal for a 993. This has gradually developed, but was more noticable for whatever reason after I bumped against the rev limiter one time. Maybe I'm too used to the smoothness of my inline-6 engine in my other car. But I would do almost anything to make this car smoother. 30k miles, 1998, C4 with no history of engine problems. Minimal rpm variation when idling.

Tom Pepper

Mark.
Do a search in the archieves regarding the idle stabilization valve. Several postings and DIY info there.
More ominously, I found my burned exhaust valve problem when the car began to idle in a rough manner.
Good luck. <img src="graemlins/xyxwave.gif" border="0" alt="[bigbye]" />

Robert Henriksen

the DIY article can be found at <a href="http://www.p-car.com/diy/" target="_blank">http://www.p-car.com/diy/</a>

Jeff 993TT

[quote]Originally posted by Mark Scheurer:
<strong>The dealer said that it was normal for a 993. </strong><hr></blockquote>

I love this line. Seems like many dealers don't know sh$t from shinola sometimes. Remind me, why do we need dealers again?

They'll say anything to placate us "customers" and get us out of there quickly.

Jeff

Pete Lech

My idle smooths out when I turn on the AC. If this is the case with your car, try speeding up the idle a tick or two. I believe details are on p-car.com.

I cleaned the ISV, but it didn't make any difference. It looked clean before I 'cleaned" it at 25K miles. Techron didn't make any difference either. I am living with it, as it isn't that bad and we use the AC a lot here anyways.

tom_993

Hi Pete,
I think cleaning the ISV is on Robin's site, but not speeding up the idle. Here are two threads that discuss this.

Tom
'95 993

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=3&t=003904" target="_blank">ISV and '95 with LWF</a>

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=3&t=002968" target="_blank">Idle stabilizer valve adjustable</a>

ZCAT3

I know bad Oxygen sensors can cause a rough idle as well. Not sure if this applies to 993s, but it does to the earlier 911s.

KASH '95 993

I too had a rough idle until last weekend that I also attributed to being 993, however, after replacing my plugs over the weekend (WAPITA), rough idle is now gone.

PS: It also turned out that the previous owner had the wrong plugs in there (dual electrode TT plugs). Funny enough, my local P-cap dealer also gave me a wrong set of plugs (dual electrode TT plugs) the first time around. If it weren’t for Robin's DIY, I would have thought everything was Ok with the new plugs since the old plugs were the same part #.

Now the car runs a lot smoother with an easy 10 WHP across the RPM range, per the trusted rear end dyno of course . Can't say thanks enough Robin. YOU DA MAN!

A word of advice to all the rough idlers out there, pull a plug and check your part # (especially if the dealer did your last tune-up).