16 valve 3.0 turbo rough idle
 

Has anyone built a 3.0L using the 16 valve head with 951 DME have rough idle problems ? I have a aluminum flywheel and lightened crank. I'm not sure how much effect it would have at idle.I have tried numerous chips even MAP system. I am running 65# injectors now but even the stock 951 injectors weren't much smoother. I built the motor myself and fabricated the intake and exhaust.There are no vacumm leaks .The cams were profiled for the turbo ,since I have went back to stock cams and still it idles no better. There seems to be a lean miss. Running richer around13 to 1 helps but is still rough. And I cant run richer without disconnecting the o2 sensor because the DME allways brings it back to 14.7 to 1. Thanks

>>> The cams were profiled for a turbo<<<

What does that mean? Scan a copy of the cam card and post it.


It's not the injectors size that's the problem. Are you sure the IAC is working properly? Are you SURE there are no vacuum leaks?

TonyG

The cams were reground for higher lift shorter duration. I went back to stock cams . I have pressure tested the system dozens of times no leaks.The idle actuator is new I have actually tried a couple different ones. I have been trying to solve this for about a year now.

Which stock cams did you go back to?

Are you sure the IAC is working (shorted wiring, or DME fault)?

How much vacuum are you pulling at idle?

TonyG

Did you bring the compression down? If so, did you preserve a combustion friendly environment in there?

Tom

The compression or the combustion chamber squish wouldn't affect the idle quality.

It's either the cams lobe centerlines/cam timing, or a vacuum leak, or a non functional IAC (or the electronics or wiring that control the IAC), a/f ratio, or ignition timing.

TonyG

IAC=?

IAC = Idle Air Control I suppose

I thought it was called the ISV=idle stablizer valve. Hmm, I dunno.

John

ISV = IAC just depends on whose words you prefer. One is a motor and one is a valve both operate in the same fashion.
__________________
Best Car Insurance | Auto Protection Today | FREE Trade-In Quote

Tony,

I did not actually make that post. You see, I have this little brother who is also named Tom who made the post while I was not looking. Yeah, that's the ticket, a little brother with the same name as me.... ;) --Tom

The cams are 1989 944S2 cam timing is set to stock. I have tried advancing and retarding the cams with the adjustment on the cam pulley but you cantadjust intake and exhaust seperately. I have 14 inches of vacumm at idle and my timing varies from 4 to 8 degrees btdc.

125250

Are you using a S2 head?

Why is your ignition timing fluctuating?

14" of vacuum is not a lot for a stock set of cams. In fact... it's pretty small...

FYI.... a stock set of S2 cams probably have more duration than you want (ie lobe centerlines fairly close), which is why you have the 14" of vacuum. Also... at what rpm is the car idling at?

Do you have individual adjustable cam sprockets? If not, then I'm assuming that when you say you are "advancing and retarding the cams with the adjustment on the cam pulley", you mean that you have one (1) adjustable cam sprocket? Or do you have two (2)? And are you using a dial indicator to set the cam timing? (of one or both of the cams?).


If you only have one cam sprocket (being turned by the cam BELT), then it's impossible for you to alter the timing with one cam relative to the other. By adjusting the one cam sprocket (turned by the belt) you could only adjust both cams together since the other is turned by a cam chain...

If that's the case... then you really can't control much...

TonyG

Tom M'Guinn

Are you sure you're not the one that purchased that mint 944 turbo... uh hem... S2, from that little old lady?

TonyG :-)

The cams are in a S2 head I can only adjust the timing sprocket for the intake opening timing. Which is set with a dial indicator. The stock cams have no overlap. Intake opens 3 dg atdc exhaust closes 7 dg btdc at .040 lift. The cams are connected by a chain so I cannot alter intake and exhaust seperately. When setting the intake with indicator the exhaust is in perfect timing with the intake according to the manual. The car idles at 850 and is consitent exept for the missing which makes the timing change slightly. Is there any way to raise the idle without the DME bringing it back down to 850? what kind of vacumm should I have for S2 motor or the 951 motor ?