Can you help me diagnose a hestitation/stutter/vibration problem!
 

I have some very slight symptoms that something is amiss with my 951 engine and I want to know whats going on in case preventive action is due.

What do you make of the following symptoms?:

• Slight hunting/uneven idle, gets much more noticable when aircon is running
• Intermittent white smoke from exhaust when idling warm. Was there yesterday, only briefly today.
• Occasional throttle lag from idle to the point where I have to disengage the clutch and wait for the engine to rev up when starting from a standstill to stop engine from stalling.
• strange occasional and very indistinct vibration or hesitation on accelleration between 2500 and 3800 revs.
• I suspect I have a lack of power/pull, but I have not owned the car long enough to be sure.

I had some cracks in the inlet pipe to dump valve hose. When I pulled it I found some small aluminium shavings inside. Any idea where they might come from? Turbo vanes?

There's a vacuum leak between airbox and MAF. But Considering it is before the sensor I don't see how it can affect the idle.

I lost the throttle screw and had to reset idle speed. I had to back out the screw several complete turns to make the car run at all. While... "Normally it will be approximately 1/2 turn open from fully seated down (clockwise)", according to Lindsey Racing. Significant? Can a badly adjusted idle affect throttle response? RPM @ idle is spot-on though.

I Will do a compression test this WE and will monitor coolant levels. I'll also try to check for vacuum leaks, but I don't want to pull the intake manifold if I can avoid it.

Def Fix that Idle and ANY AND ALL Vac leaks,. They can cause all kinds of silly problems

The easy stuff.
White smoke is usually coolant.
Do a compression test ---remove DME relay or you will wash cyl with gas.
Do a leak down test--Harbor freight tool---watch guage and look in coolant reservoir tank and listen at rear exhaust pipe for hissing, and bubbles.
Compression-leakdown test

Hesitation.
Video by HondaDustRs video and fix of the MAF.

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http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/493906-air-flow-meter-fix-refurb.html

Throttle body.

The first thing most do is adjust the TB. You have to have all your vac leaks fixed and the AMF working before you adjust. There is a TB repair kit.

You may have a dirty ICV/ISV (idle control valve/idle stabilizer valve). Remove and clean. Check the hoses for cracks.

You may have to remove the intake to do all the repairs correctly. When you do there are a lot more WYAIT things to do.

GL
John_AZ
1988 924S + 1987 924S

Thanks for your answers.
I'll do a compression/leakdown test and base my approach on that.

Any thoughts on the aluminium shavings?

So i broke the cover on the airflow meeter and cleaned the slider. My car has only done 62K miles and the unit was spotless. I then proceeded to check for vacuum leaks using a coffe cup in place of the MAF and a bicycle pump connected to the banjo bolt on the intercooler intake pipe.

The cam housing seal is busted. Lots of air somehow eascapes from the head up into the cam assy. Does this mean that I need to replace the valve stem seals?

(I may off course have other smaller leaks but I'll have to fix this large one to find out.)

I still have not been able to pinpoint where the metal shavings in the intake system come from, and I'm still waiting to do a compression/leak down test.