924S running issues with video

[PRBob]

Hi,
Having trouble with my 87 924S after going through just about everything that I can think of. It is idling very roughly and high. Frequently missing and occasionally backfiring. It will sputter and die if I don't keep my foot on the gas until it warms up. Here is a video: Sometimes, it will die when trying to idle. Then occasionally, white "mist" (not really smoke as far as I can tell) comes out of the intake very slowly and dissipates very slowly. Looks like coolant to me?

It was running fine in 2013, then one day would not start. I cleaned starter and ground contacts, and found that fuel pump was dead. Replaced it, fuel filter, and the fuel lines with push-lock hoses and AN fittings and then got it to fire up but it immediately ran approximately the way that it does now. Got a fuel pressure gauge and fuel pressure seems to be at spec. Replaced spark plugs, wires, cap and rotor, speed and reference sensors, throttle position switch, adjusted MAF to spec, checked for all vacuum leaks and replaced all hoses. Replaced the ECU with a rebuilt one. Checked DME Temp sensor. Rebuilt fuel injectors and verified they are spraying evenly.

Brought the car to a Porsche specialist and they supposedly tested everything but could not figure it out without opening up the engine. To them, it sounded like a broken valve spring. So I began to tear it apart myself. There was no broken valve spring. Had the head professionally rebuilt for good measure. Replaced gaskets, timing belt, balance belt, water pump and all rollers/bearings. Verified timing is correct per marks. (have not checked with a timing light but it should be ok?). Cleaned all grounds under hood and chassis. Tested ignition switch and new fuel pump relay. Compression was consistent (average 185? iirc) within 5 psi of each other on all cylinders. Tried BG-44K fuel additive and 93 octane fuel. I am sure that I have tested other things that I am not thinking of right now.

Here is a video: https://youtu.be/pnwuHBbJUzI

Any idea what else I should try?

[dgcantrell]

Have you verified the timing marks on the balance shafts? That thing is shaking bad at idle. Also sounds like a motor mount is bad too.

[pdxfj]

Last time I saw an engine run like that on a 951, they had forgot to install one of the gaskets on the intake manifold. Once that was fixed, it ran fine.

Kinda seems like a massive vacuum leak to me..

[Tom944]

Sounds like one injector got clogged when you worked on the fuel system. Check the plugs to see if one looks different. I had good luck with a refurb injector from our host.