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)

Hard Start After Sitting (Cold Start)

Recommended Posts

My 99 996 for the last couple of months has been starting hard when it's cold or I haven't driven it in a week. Once it's warmed up, it starts fine. I did see on a post on here about a fuel pump going bad. I have just replaced my battery and my starter was replaced last year, along with the wire that runs from the starter to alternator, just so everyone knows those issues have been fixed for the warm starts I have had before.  The car runs great once it's running, no rough idle or anything. Any ideas would help.

Edited by R996
Link to comment
Share on other sites

  • 1 month later...

Most common fails on electric pumps.... In no particular order. (Based on general cars not just porsche... )
Fuel Pump - Basically they wear out.

Fuel Pump relay - Same,, sometimes they can get sticky from age and with enough attempts they will work but its a warning.

Check valve in Fuel pump. - Still have to replace the pump to fix problem, but I have gotten them to work by removing the pump and soaking the internals down with seafoam ,, they varnish up with age and seafoam will desolve it.. Its a fussy job ,, good for a winter weekend and a good beer..


If you have a scanner hooked up (Durametric or PST ) You  might catch a code if you dont keep trying just try once and stop..

Weak sensor like CPS/TPS/IAT etc.. can cause this symptom..

If Equipped,, It can also be the e-throttle needs to re-sync,, just start cold, turn the ignition on and let sit for a few minutes, you should here the throttle cycle..

If its a mechanical version the TPS can cause a slow start ..



Link to comment
Share on other sites

  • 2 weeks later...

It sounds more like the fuel pressure regulator to me than fuel pump or relais.

Apart from controlling the pressure it also keeps the fuel rail under pressure to avoid fuel vapour forming in the rail when the car is parked up with a warm/hot engine.

In your scenario the pressure in the rail is not maintained but instead bleeds away through the FPR into the return line back to the tank.

Next time before a cold start run the fuel pump by bridging/shorting terminal 30 and 87 of the fuel pump relais. As soon as the sound of the running pump remains the same, start the car.

If it starts normally then it's the FPR.

Another test for this would be to clamp the fuel return hose shut next time you park the car for the period of time that would lead to difficult starting. After that time has passed, remove the clamp and start the car. If it starts normally then it's the FPR.


Another reason could be leaking injectors that bleed off the fuel into the cilinder

Edited by hardtailer
added hint regarding injectors
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • 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.