Copilot

So, abnormal issue with my car. Started today, after many months of running fine and no real major tweaking to it.

Car started up, drove fine, and after driving for about 10 minutes, I decided to "get on it". Drove it fairly hard for about 10 seconds, and noticed when I got off the gas I had the red warning light on - then realized the car had died.

Restarted, and then wouldn't idle - as long as I keep my foot on the gas, the car runs, accelerates - heck, even drives, as I got back. Sometimes it would idle on its own, other times it wouldn't.

Now that I'm parked, it basically won't start. Also, when I do start it now and stay on the gas, it sounds like there's a bit of a rattling up front - I'm not sure where from, and that may just be me acting hypersensitive to everything I'm hearing.

I've checked all the vacuum lines, except the ones that connect to the wastegate and the MBC (but I've given them a tug to see if they'd popped loose). They're all silicone lines and all new within the last 2 years. I did some searching and while I couldn't find any other exact threads describing my issues, I found similar issues and have checked the following:
-DME relay (jumped it, no issues, relay seems fine)
-throttle set screw (in place, no leaks felt)
-ISV - jumped it as per Clark's Garage, no changes
-TPS - disconnected and started it, no changes

I'm at a loss as to what it could be. Any guesses?

All the work/mods I've done to my car should be in my signature, I'll edit if there's anything there I've missed.

Dougs951S

How much vacuum are you pulling at hot idle? sure sounds like you blew something loose. start the car cold and put your hand on the ISV, you should feel it vibrating as its doing its thing. If the ISV were not working for whatever reason, jumping it wouldnt do anything so that doesnt rule out an ISV issue. Also check your maf.

Copilot

When I've got my foot on the gas (as it won't actually idle on it's own), at about 1k rpm I'm showing -18 on my boost gauge, so I'm definitely getting vacuum. You're right about the ISV - that makes sense, jumping the ISV just causes it to motor right? I'll see if I can get someone to assist and start the car for me so I can check, because like I said - no foot on the gas, no run.

Copilot

Update - went through and double/triple checked everything else (ie. timing belt didn't skip, etc.). Anyways, after letting it sit for a day or two, got in, turned the key and it started and held an idle. A little rough/low, but it worked.

Didn't feel the ICV doing much - it was vibrating a little bit, but then again - that was probably mostly from the engine vibrating.

My friend, who just bought a 951 3 days ago, was there helping me troubleshoot and I was going to show him how to jump the ICV via the test port (per the procedure on Clark's Garage). As soon as I connected the wire, the car died. Not knowing much about the ICV, I'm assuming that jumping the test port is supposed to set the ICV at a fixed rate, and when I jumped a (presumably) bad ICV, it caused the car to die.

Good theory? Safe to say the ICV is dead?

Dougs951S

When the ISV is working correctly, it will be vibrating with the key on, engine off. its very obvious, it vibrates at about 12 hertz. Jumping the ISV basically takes it out of the airflow circuit by setting it to the neutral position, the position it should be in on a correctly running, fully warmed up engine that is just sitting there idling. The reason you jump it when adjusting the base idle is to give you a good "centerline" base to allow the isv adjusting room in both directions. If your car died when you jumped it, you have another issue. Did you try raising the idle with the isv jumped to see if the car would stay lit? Plug in the ISV from your friends new car just to test it. They can easily be changed without removing the intake.

Copilot

Well, ISV is fine. Anything else it could be? I've noticed there's kind of a loud/rough running noise when it starts now - not sure what it could be. Any ideas anyone?

Copilot

Alright, so here's where I'm at with this.

The car will now start, and hold an idle - however there's a very concerning knocking noise when it idles. I'll capture a video of it and put it at the end of this post. When you rev the engine, sometimes it will die, and sometimes it will drop to 300-500 rpm, then recover back to a normal idle around 850 rpm. I haven't tried to drive it, as the knocking noise (which sounds like it's coming from the top of the engine) is a bit concerning. The rod bearings were replaced approximately 300 miles ago, so I have a hard time believing that's the issue.

Also, when I AM on the throttle, it seems to be smoking pretty bad - hard to tell the color because it usually clears pretty well by the time I get out of the car, but I don't think it's white - I'm not getting any oil in the coolant or coolant in the oil, and the a compression test I did a few weeks back looked like it all worked well. When I get off the throttle, then no smoke.

Here's what I've done so far in efforts to troubleshoot (some were good maintenance items too):
--new fuel filter
--swapped FPR
--checked vacuum lines
--replaced ISV
--checked throttle body
--checked MAF
--checked TPS adjustment
--new spark plugs
--new coil
--checked distributor cap and rotor (both 300 miles old)

I am at a loss as to what this could be - I think I've all but ruled out a headgasket failure (correct me if I'm wrong though) - I pulled the DME relay and had my wife crank the starter, no bubbles or air coming through the expansion tank.

Here's the video:

Copilot

One more development - the last time I tried to start it, I cranked the engine and there was a horrendous wail/squeal; because I like to live dangerously, I cranked it again, and it did start -subsequent starts yielded no squeal.

Here are the possibilities that I'm thinking could be the problem, but let me know if I'm off base -
1. Spun rod bearing (which would suck, because I replaced them only about 200 miles ago
2. Broken valve spring/other valve issue
3. Broken lifter
4. Scored cylinder wall

Anyone??? What is killing me is that other than this issue, my car was in amazing condition and was running SO well...

Brantley

Strange sound / rattle indeed.

I had a similar ruff idle develop that came on after I "got on it". Turned out to be caused by a failing fuel injector. Replaced it and all was well. Perhaps something to check...

Dougs951S

1. A spun rod makes the most terrible knock you've ever heard in your life, and its way louder if you listen for it by the oil pan. Its hard to hear from the location of the camera, but a video shot from under the car will be very telling.
2. Potentially. Do a compression test, if you have a valve that isnt closing properly, it will be revealed.
3. Hate to tell you but it sounds more like a rod than a lifter. Its too low pitched. Lifter tick is usually a high pitched tapping sound, not a deep knock.
4. If the rod bearing is spun, there is a high possibility and you might not see the telltale signs if you JUST spun it, but a motor with scored walls will tend to smoke, especially on boost.

Worth noting that your idling issue has nothing to do with the knock most likely, unless the problem IS in the head.

Copilot

Okay, so time to update the thread.

I have pretty much resolved the idle issue. It would appear my main issue was a conglomeration of vacuum leaks - minor - anyways, I resealed the throttle body (or rather, just swapped in a known good one) and replaced the bypass valve (the one I had was adjustable, sticky and needed to be cleaned), and the idle issue seems to be okay. It still died when I jumped the ISV, but it would appear that was simply because I had the idle set too low - I turned it up, and it now survives when you jump the port - success!

Also, during the down time I replaced the head gasket, had the head reworked at LR, and everything on the top end is good to go - piston walls are all fine.

However, the rattling noise (which wasn't the initial symptom I had when this all started, but arrived afterwards) - that's still there. It really doesn't sound like a rod bearing - it's no louder under the car then on the top, and it really does sound like it's coming from the top of the engine.

After some searching I read about similar noises with a loose cam bolt. I went and checked mine, and while it wasn't "loose", when I took my torque wrench to it, there was significant movement when I tried to torque it to the proper value (something like 65nm or something, right?). So, the bolt was a LITTLE loose. I also read the original bolt can't be retorqued - the bolt on there was replaced about a year ago when I did a whole slew of seals on the car, but I don't know if it was a "new" style bolt or not - didn't know that was an issue when I did it. Anyways - does it sound like a loose gear could be the issue, based on the noise in the video?