lumpy idle

[Mike]

having enthusiastically chased a 911 on private winding road I'm now experiencing very lumpy idle, slight overheating, smelly exhaust and slight loss of power when flat out. Having searched, the following are possible, but what is most probable? answers on a postcard to the usual address! cheers

1. ECU
2. lambda
3. AFM
4. plugs
5. coil pack/leads
6. CAS
7. air leak
8. throttle sensor
9. head gasket
10. timing belt jumped a tooth or two
11. air regulator (just behind throttle)
12. fuel filter/pressure
13. bent valve
14. holy piston
15. turbo gasket
16. dodgy injector
17. hydraulic valve lifters

[sx loony]

check air flow meter,if running lean i could have fooked the plugs

[Si]

14. Hg

[Mike]

14. Hg

mercury of head gasket?

[John Bennett]

I'd say 7: air leak is most probable.

May be worth doing a compression check anyway, to see if a valve has started to disintegrate or a piston ring is going, and you get to see if you've just melted a spark plug as a bonus

[DAVE610]

You didnt list faulty regulator, fuel pump, or dodgy injector..

[Mike]

You didnt list faulty regulator, fuel pump, or dodgy injector..

what's a regulator? do you meen the fuel pressure regulator?

[cranky]

Well lumpy idle and poor performance is usually turbo gaskets

[Si]

mercury of head gasket?

Yes, err, that's what i meant, as in, ummm. low pressure, ummm, bosot leak

(Did I blag my way out of that one OK, do you think anyone noticed?)

[Mike]

ECU reset and topping up with oil didnt help..

next step plugs out and FMIC off

[Mike]

having enthusiastically chased a 911 on private winding road I'm now experiencing very lumpy idle, slight overheating, smelly exhaust and slight loss of power when flat out. Having searched, the following are possible, but what is most probable? answers on a postcard to the usual address! cheers

1. ECU
2. lambda
3. AFM
4. plugs
5. coil pack/leads
6. CAS
7. air leak
8. throttle sensor
9. head gasket
10. timing belt jumped a tooth or two
11. air regulator (just behind throttle)
12. fuel filter/pressure
13. bent valve
14. holy piston
15. turbo gasket
16. dodgy injector
17. hydraulic valve lifters

Work done so far:
- compression test 10bar each cylinder OK
- disconnecting every injector/plug in turn makes engine run equally worse
- spark plugs fine
- coil pack/leads swapped for my spare set
- no air leaks (that I can find)
- fuel pressure spot on
- battery disconnected for 24hrs and ECU reset

More on the fault
- car runs fine over 2000rpm but just before it dies, if I blip the throttle, there's a loud "click" or two from the area around the injectors and it sounds like it's backfiring up the plenum!
- I dont think there's anything wrong with engine, plugs, coilpacks, ECU, exhaust or inlet piping
- If I disconnect the AFM, car runs steady at 2000rpm and opening throttle makes no change to engine revs

Thoughts
- I cant get lower crank sproket off so cant check timing belt... how do you do this?
- could it be lambda? how do I test?
- AFM sounds dodgy? what do you think?
- could it be throttle sensor not working at low rpm? how can I check?
- what about CAS? Car runs fine over 2000rpm, though
- any other ideas

Cheers!

[nismojon]

hi mike
sorry to hear you still problems told you that your car was not going to be to happy at 210mph
back to the problem does the idle change whether the engine is cold or normal running temp?

[Kev]

sounds like headgasket to me mike.
take rad cap off and check for rainbow water.
take oil cap off and check for mayo.

failing that, u think it would make it to crail on sunday?
im planning on heading up.

Kev

[Mike]

i'll check tonight...

idle problem does not change with engine temp

[Mike]

oil and water are fine...

prob not go to Crail unless I get really stuck then I'll be down later in the year

how would I know if AFM was the cause?

[Kev]

pretty certain its not the afm Mike, fault is ares for elbow.
if it was over 2k there was a prob, id be looking at afm.
what were the comp test results?
sounding more like air leak then if oil and water are ok.
get it on idle, a can or kettle of water and pour a steady stream over the plenum-manifolg seal and then manifold to head seal.
If they are ok, then id guess one of the regulator pipes from aac or idle control

[Mike]

pretty certain its not the afm Mike, fault is ares for elbow.
if it was over 2k there was a prob, id be looking at afm.
what were the comp test results?
sounding more like air leak then if oil and water are ok.
get it on idle, a can or kettle of water and pour a steady stream over the plenum-manifolg seal and then manifold to head seal.
If they are ok, then id guess one of the regulator pipes from aac or idle control

wouldnt the plenum suck the water in? how do you see a leak?

comp test 10 bar all four cylinders dry

[Kev]

if the plenum does suck in the water, u have found the problem
ie it has a leak

[M.D.]

to be honnest it sounds like you have jumped a tooth on the cam belt and had slight valve contact, check to see if your still getting the boost your used to and open the window and listen for pinking

[JonnySpeedbump]

Mike, as Kev mentioned it's pro'ly not the afm but you can do an easy check to help eliminate it from your suspect list:
Remove the air filter, then the afm (think it's 4 x 10 or 12mm bolts and a jubilee type hose clip).
Look through the afm and you should see a tiny component/sensor held in the airflow by a thin wire at each end. If it still attached and not covered in guff then it's probably fine but you can use a non-abrasive alcohol spray like Colclean to gently rinse it. I know some folk use a cotton bud with alcohol cleaner but I would be worried that it might break, it's pretty delicate.
I've used it on my afm a couple of times and it does make a noticable difference to throttle response.
Good luck diagnosing it mate.
Jonny