GTS 1993 - yesterday changed the air filter, oil & oil filter and plugs - ready for SITM.
Car ran perfect before but after has a stumbling idle, in drive it feels like its missing and wants to stall. RPM's are at about 500 to 550. In neutral it feels a little better and the revs come up to 600 to 650. Still not right.
Drive the car and she screams - no issues there.

Plugs are genuine Porsche 3 electrode.

How can I test for a bad plug?

I guess I will change out all the plugs and see if that makes a difference.
Need to let her cool down for a while though.

Thoughts anyone - if you are awake 8>)

 

Any chance you damaged one of the plug wires when removing them?

 

Hi Roger,

I have found bad spark plugs in the past by checking the amount of resistance in each plug. Using an ohmeter, check the resistance between the center electrode and the sparkplug connector end. The resistance should be consistent across all plugs. An "open" reading means the plug has an internal break.

Also check for an internal short to ground - all plugs should read "open" between the sparkplug connector end and the threads.

Hope this helps,
Adam

 

Afshin,
They look pretty good and I was carefull removing them.

Adam,
Thanks for the tip and I will pull them all and check them out - at $10 each they better be good.

 

Do you need me to swing over and lend a hand?

 

Did you re-adjust your idle with you hammer?

Computer could be trying to compensate for something new.

Paul

 

Obviously a problem caused by the damn slush box. Put in a 5 speed and you'll be good to go.

 

**** off Cheryle 8>)

I checked the car after the swap with the Hammer and no faults.
Also did an idle stabilisation - that worked fine as well.

In the middle of pulling the plugs. back in a few.

 

Touchy 'ol bugger. Play nice and if your problems persist maybe Randy will loan you a nice one for your road trip. It has a real transmission, should cut half a day off the trip time.

 

Isn't it because that GTS has that silly torque converter that's dragging the engine down? Wouldn't happen on a 5-speed

Dan
'91 928GT S/C

 

Air filter upside down ?

 

Roger i would pull both of the coil wires and inspect them and do a test run in a dark garage spray some water onto the wires with the air tubes removed, its a good chance your wire set had gotten damaged or one of the plug connectors has gotten damaged from pulling the wire out/ I would also suggest that you put a set of the Bosh copper tips in they are the least expensive and seem to work the best, also check the plug gap IIRC its .028 in. Bosch PN is 7900

 

I second the coil ...or check the ign monitoring circuit...could be bad signal from temp sensor?...

 

He just didn't have me to the plug change.

Details to follow.

 

When you change the air filter you left an oily rag on top of the MAF? j/k

The way I check for bad plug or wire is to remove them one by one to see if the idle worsens are remains same. If you pull the bad one the stumble will remain and you've narrowed the issue. Replace that plug and/or wire and back in the biz.

BTW I use a pair of plastic pliers designed for the job.