Jump to content

Welcome to RennTech.org Community, Guest

There are many great features available to you once you register at RennTech.org
You are free to view posts here, but you must log in to reply to existing posts, or to start your own new topic. Like most online communities, there are costs involved to maintain a site like this - so we encourage our members to donate. All donations go to the costs operating and maintaining this site. We prefer that guests take part in our community and we offer a lot in return to those willing to join our corner of the Porsche world. This site is 99 percent member supported (less than 1 percent comes from advertising) - so please consider an annual donation to keep this site running.

Here are some of the features available - once you register at RennTech.org

  • View Classified Ads
  • DIY Tutorials
  • Porsche TSB Listings (limited)
  • VIN Decoder
  • Special Offers
  • OBD II P-Codes
  • Paint Codes
  • Registry
  • Videos System
  • View Reviews
  • and get rid of this welcome message

It takes just a few minutes to register, and it's FREE

Contributing Members also get these additional benefits:
(you become a Contributing Member by donating money to the operation of this site)

  • No ads - advertisements are removed
  • Access the Contributors Only Forum
  • Contributing Members Only Downloads
  • Send attachments with PMs
  • All image/file storage limits are substantially increased for all Contributing Members
  • Option Codes Lookup
  • VIN Option Lookups (limited)

Recommended Posts

Posted (edited)

Hi all - First post!

 

I'm slowly but surely working through the list of fixes on my new (to me) 996 and this one has me a little stumped so far. It's a 1999 C2, cable throttle.

 

Every time I start the car from cold I have an issue where it fires immediately up to the normal 1800/2000rpm for a split second and then stumbles badly straight back down to about 400/500rpm for a second or so before something (the ecu?) kicks in and it jumps back up to a rock solid cold idle at around 1100/1200rpm.

 

When it's warmed up it stays at around 6/700rpm with AC off, 900rpm or so with it on. Again, rock solid. Never had it stall, never had it run rough, pulls hard etc.

 

Fires up immediately to a nice steady low idle without this issue when warm. This stumble only appears on cold starts, but it doesn't sound too happy about it and I'd like to try and fix it. It's not normal behaviour based on my previous 996 and 986.

 

It's got a new air filter and I've cleaned out the ICV. It recently had a new water pump (and the bearing was really grumbling in that so wondered if that was 'dragging' the RPM's down on a cold start until the ECU could compensate) but nothing has cured it.

 

I'd planned to do plugs and coil packs soon, as well as sort out a leaking spark plug tube, but not sure what else to try.

 

The only thing I had considered was that when I picked the car up it had an old K&N kit on it that I removed and replaced with the OEM airbox. I reused the same MAF sensor (after a thorough cleaning with electrical contact cleaner) but didn't think the MAF was used in a cold start (might be wrong here...)

 

Any ideas?

Edited by Mallone

Share this post


Link to post
Share on other sites
    You can remove these ads by becoming a Contributing Member.

:welcomeani:

 

Could be the solenoid in your ICV is gotten weak.

After all it is 20 years old.

 

Yes, the MAF does nothing at idle. It comes into play above 4000 RPM.

Share this post


Link to post
Share on other sites

👋

 

Would a failing/old ICV not exhibit other poor idle issues? It’s absolutely rock solid the rest of the time.

 

Or are you suggesting the solenoid is just slow to respond when first fired up/cold?

 

Any way to definitively test it’s working correctly?

Share this post


Link to post
Share on other sites

You can test the ICV by removing it from the throttle  body and cycling it with a 9V battery.  It should move smoothly and not bind.  Make sure to clean all the gunk and carbon from the rotating valve body inside the ICV.

Since you replaced the air filter with a stock box, reset the DME/ECU by disconnecting the negative battery lead for 30 minutes, then  reconnect and go for a 20+ minute drive to allow the DME to re-establish sensor values.

Share this post


Link to post
Share on other sites

Thought I'd give an update on this as I'm still struggling to diagnose/solve. 

Tried with the MAF disconnected. No change. Issue remains. 

Replaced the ICV with a new one and also pulled the throttle body and gave the entire thing a thorough cleaning. Idles cleaner generally, but still the same cold start problem. 

Did a major service and gave the car a set of new plugs and coils. Issue still there. 

I'm now running out of ideas  

The car sounds quite 'hissy' when it's first started so starting to wonder if there might be a vacuum leak somewhere that's causing the issue that the ECU is compensating for? 

The 'hissing' goes away when warm so could just be a cold start thing. No SAI on this car, if that makes a difference.

Also get quite a bit of chain rattle on this car, would the tensioners coming up to pressure have anything to do with it? (doubt it, but worth asking!) 

Any other smart ideas before I start to think about taking it to a garage?

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.