samana76

Hello Everyone,

I've written about my 951S before and have always received fantastic help from everyone here. So here goes my new list of problems which I hope you all can help me with once again.

My 951S has been acting up in the recent weeks, having difficulty starting in the morning, smoking at start, sputtering when cold and not having a stable idle.

I did some diagnostic myself and feared the head gasket, which I had replaced only 7 months ago, had given out.

To be sure I brought the car to the very reputable garage ModderMan in Palo Alto, CA and they gave it a look through.
They checked the pressure in the cylinder and did a leak down test and said it the numbers are absolutely perfect. Which is a relief. However symptoms remain.

The guys at ModderMan replaced the spark plugs which were fowled (NGK NGK7ES which I had put in by them less about 5 months ago). They prefer the standard plugs and so installed those this time around.

They also told me the exhaust manifold has a small leak, which I can hear "pssst"ing in the morning when the engine is cold. It goes away when the engine is warm and the metal expands, but that's something I will have to take care of soon.

Also the engine runs rich and burns oil. In fact my air/fuel ratio indicates 11 while cruising (instead of around 14 I was reading not long ago) and 10 at idle.

Regarding burning oil, it's always done that, but I think more so now than before. The guys at Modderman think it might have to do with the turbo, but could not confirm until they look into it more deeply.

Also I noticed is a unique sound, like a high pitched machine gun sound, coming from what I think is the waste gate area when the turbo kicks in at high RPMs. I installed a new waste gate less than 1 year ago, so I don't think it's bad, maybe just dirty or there could be a vacuum tube not hooked up correctly. In fact another thing I noticed is that my vacuum gauge indicates slightly less vacuum when idling than it was before - is closer to 15 now compared to around 18 no long ago.

Finally I am posting two videos of the idle hunting problem I've been having for a while. However it is getting worse and becoming a real pain, so this is one of the things I would like to fix right away. As you can see when I stop at an intersection the idle goes up and down like a pendulum constantly. If I wait long enough, typically it eventually gets closer and closer to the correct idle, but it take a long time. If I "help" it by accelerating and very very slowly releasing my foot so that the RPM tapers to the correct idle speed, then there is little to no hunting. What can this be and how can I correct it?



Sorry for the long post. It's just that for some reason these problems pretty much started all at once. I spent quite a bit of time and money sorting and having a specialist sort out my 951s and am a bit frustrated that all this is going on now.

To help you all out in giving me suggestions I will list all the changes and upgrades I did to my 951S from stock here:

- installed 3.0" Fabspeed performance exhaust package
- installed Tial 38 dual port waste gate
- installed Rogue's A-Tune Package
- installed a Lindsey Racing manual boost controller
- installed an Autometer Sport Comp Boost gauge model 3301
- installed an Innovate Motorsports Air Fuel Ratio gauge with wideband controller and oxygen sensor
- replaced spark plugs with NGK BPR7ES (now have new stock spark plugs as per ModderMan’s recommendation)
- installed Lindsey racing adjustable Fuel Pressure Regulator and gauge and set to correct fuel pressure for A-Tune

Thank you all for your help.
Igor

travisgreen

Have you replaced your coolant sensor? If it's bad it could be running closed loop even after car is warm

V2Rocket

Is your bypass valve/recirc valve original?

Van

Or maybe the TPS or AFM is dying, and signalling that more air is going in - so the computer puts in more fuel... but actually less air is going in?

bonus12

I definately suspect the tps. Exhaust leak at manifold is probably.what causes smoke at start (I also have the psst psst sound and smoke at start. I can also smell exhaust near the manifold at this time. And it does sound like there is another vaccum leak somewhere.

travisgreen

If you have an exhaust leak at the header, your wideband isn't getting a correct reading and neither is your oxygen sensor. You also say you can hear a vacuum leak. You clearly have multiple issues so you need to fix the obvious before looking further...

konakat

TPS would cause problems under power more than at idle, so I am not so sure it is that. A vacuum leak can certainly cause this sort of issue and since you have indications that you have a leak I would pursue that. A vegetable can with a compressor fitting can be shoved into the air filter hose, then you apply a few psi of pressure and spray everything down with soapy water to find the leak. It could also be a worn spot in your AFM, see this guide http://www.the944.com/afm.htm.

doabarrelroll

+1 on TPS. Also, verify for vacuum leaks.

catamount

My car did something very similar at idle. It turned out it was the TPS.

samana76

Hello Everyone,

Thank you all for your suggestions. The general consencus, then, seem to be that the TPS is at fault regarding the erratic idle behaviour. I will test is this Sunday by following the instructions on Clarks Garage.

Regarding the richness, this morning while driving to work I noticed that at WOT the air/fuel ratio stays steady at 14. So basically the A/F numbers are as follows:

At steady idle: A/F 10
At cruising speed: A/F 11
At wide open throttle: A/F 14

Hope this information gives some better insight to what the richness problem might be.

I guess if I drive at WOT all time I won't have a problem then... except with the local CHP.

Thank you all again for chipping in.
Igor

Ben951S

At WOT, you want to be between 10.8(safe)-12(starting lean). 14.7 at idle, a little under on partial throttle.

samana76

Hi Ben951s,

Yes, that's actually my point: I find it very strange that I am getting basically the opposite of what I should be. Do you have any suggestions on what could be causing this?

Thanks for you help.

bonus12

Sorry about my confusing post. I was responding to OP, and I do not have a vacuum leak.

Dmitry S.

Hi Igor,

I have a spare TPS (along with other parts) if you need one. It's in Cupertino - you're free to borrow it this weekend.

-Dmitry

samana76

Hello Dmitry,

Thank you for your offer. Sorry for not getting back to you earlier. I was hoping to work on my car this weekend, but today, Saturday, I am working and tomorrow I will be out of town. I will try to check my TPS this week to see if it is the culprit of my idle hunting and, if so, maybe I can come down next Sunday to pick yours up. I will post my findings here and PM to schedule for next Sunday.

Thank you Dmitry and everyone here again for all your help.

Wish you all a great weekend.
Igor