986 2.5 rough running

[robert.hetherington]

Hi. I've just bought my second boxter - a 1998 2.5 986. Registration number M28NUS. The car came with no service history and runs very lumpy at low revs. It was idling high and hunting so I changed the idle air control valve and it idles at 900rpm and isn't hunting. But it still runs lumpy at low revs. It's fine above 3500rpm, but below that it's the power delivery is very jerry.

Does this sound like a problem anyone else has experienced and fixed?

Appreciate any help.
Thanks

 

[CLIFFWILKINS]

Hi.
Could be the Maf try cleaning it with air mass cleaner first see if it makes any difference . It may need replacing if it doesn't make much difference.
Good luck with the fix

 

[Motorhead]

Hi Robert,

As Cliff says, cleaning the MAF sensor would be a good starting point, and check for air leaks in the induction system. Rough running can also be a function of a faulty coil-park, or even a sparking plug, so that’s something to check-out too. If it’s a high mileage car then maybe a tired Lambda sensor is a factor, so removing and cleaning them could help. Since the issue is engine rpm dependent the problem could lie with the VarioCam system.

It’s well worth running a proper diagnostic check to get a better insight as to what’s causing the problem, otherwise you’re just shooting in the dark.

Jeff

 

[malarcy]

You can prove the maf by disconnecting it. Car will run on a default map happily. If the symptoms change massively you know where to look.

Would 100% echo the Porsche specific diags before you get too deep in swapping or cleaning parts. You don’t know what baseline you have and if interventions don’t resolve anything you run the risk of introducing new problems, especially my if you introduce used parts - get a reader. Check and record all the codes and then clear them. Any that return are current active codes and will give you somewhere to look.

Without that baseline it’s all guesswork.

That said. As per other replies. That kind of issue can be related to Variocam solenoid or actuator. But you need info before you start going down that route.

 

[CLIFFWILKINS]

Yes agree with above quickest easiest solution get it plugged in to a diagnostic.
Visual check you can check the rubber induction hose they split in the grooves need to carefully pull gently apart see if split.