Mid range hesitation

Hi chaps I have a 996.1 tip with 86k miles on the clock, It pulls well at low revs, nice and smoothly until it gets to around 4500 - 5000 where it noticeably holds back the power and hesitates it's way through. ive owned the car about for about 3yrs, I've not really used it that much due to other projects and work etc and the fact it needed a torque converter (that has now been fitted). The engine has been apart 20k ago with new liners fitted, it has a stainless exhaust. I had an MOT this week and was told the emissions were off. I do have a local rolling road to call on but wanted some thoughts from some experts in the meantime. It's about time I got this sorted and started driving it for what's its intended for! Any thoughts on where to start looking?

I had something similar a few years ago, the car one morning would not go above 112mph (I can't remember the revs) heading home after a road trip, we were going through Germany and everyone else f****d off at warp speed, I just sat at 112 for the duration of the journey until I managed to catch everyone up once they slowed in Belgium. For a while I couldn't work out what the problem was but even though the spark plugs were only a few thousand miles old, one of them had broken down and needed replacing. This cured the problem straight away. Check plugs, coil packs, MAF, fuel pressure, etc

Variocam solenoid comes to mind. Really need to run diagnostics to check all of the above before randomly changing components.

Sounds like what infrasiler's said, then after that I'd also be thinking variocam solenoid.

Thanks guys, i think mine being a '99 is pre variocam?

If you had a Boxster and told me it didn't want to rev above 4500 RPM then i would be saying replace the maf as that is the fault .. 996 is slightly different in this respect but i would still be giving the maf sensor a good look first . Faulty maf will also cause emission problems . 99 is vario cam but not plus so only one solenoid .. only the cam timing is altered .

I did a bit of research and a lot of people who have MAF faults also experience rough idle and CEL light, I got neither of these issues but it does sound like it could be at fault. Does anyone have a link to a diy MAF switch check?

Pulled the MAF to see if there was anything obvious, gave it a blast of contact cleaner and reinstalled it. Started the engine then disconnected the plug mainly to see if I'd get a CEL, no dash lights illuminated but the engine did hesitate as the plug was pulled. Didn't get chance to drive it but having some new tyres fitted Saturday so will test then.

I doubt you will find a test for these ... other then unplug and drive it to see what difference it makes . Be aware that doing this can mask other issues so it's not a conclusive test . Ignition on and with a tester then the voltage should be 1.0 volts .. with a +/- of 0.1 .. outside of this its toast .. well you can try cleaning it but its faulty . I have in the past scoped a new one verses a defective one .. i couldn't see any difference hence its a clean or a replacement .. a doner one ( garages tend to have some kicking around ) to prove the fault . You get many different types of faults with a defective maf .. i have seen a misfire on X1 bank before .. maf was the cause .. idle faults .. lack of high rpm .. etc etc .. This is kinda a key component in the fueling so you can get different faults depending on what's wrong with it . Either way its something that needs ruling out so you can move on .

Thanks for the explanation Demort, looking at the varying costs of the MAF sensors any reason why I shouldn't buy this one?

So the MAF sensor arrive and I fitted it after work, if anything it wasn't idling as smooth as normal from cold but that's just my initial thought. The idea was to move some cars around and go for a drive, then the rain came :sad: I also bought a cheap OBD-11 Wi-fi tool so stuck that on and had a quick mess about, now I have no previous experience of any diagnostic software as all my previous toys have not been new enough to warrant it 8) only thing I could see was that I had an 06 fault code. Now maybe I have to clear the memory first then go for a drive and see what codes I get I'm not sure but hopefully one of you guys could advise. Like I say the MAF may have sorted my fault but I won't now know until the weekend

If you clear a fault code in the DME ( engine ecu ) then it will reset the adaptations .. basically the car adapts fueling for small issues in an engine to maintain optimum running shall we say . Photo of fault codes and post please if possible . a Reset or a replacement of a component such as this (a major part when it comes to fueling ) and the car will need to relearn its adaption values again. let's say 20 miles . if you still have hesitation then obviously it's not this .. but you do need to give it a bit of time to " get used " to the new sensor . I have one other possible item that might cause this and one that will not generate a fault code .. that's the fuel pump .. basically it can't deliver enough fuel at high rpm or on a quick foot to the floor situation .. it will hold back . no way of testing this so it's replace on a wing and a prayer to see if its the problem . Drive the car with the new maf then report back

Thanks DeMort Will report back over the weekend :thumb:

Happy to report that my issue seems to be sorted. Went for a good drive as advised and now I have full power :thumbs: Would love to chat but off for another drive :grin: