Even since I've owned this car, it runs ruff when first started 85% of the time. I don't mean cold start, started period. It gets worse when it's already hot. But it does this every time. Cold, hot. Long wait, short wait. 8 months of sitting, or just turned off and back on. It will start, RPM goes to about 1200, then falls to around 800. And it bucks, kicks, spits, and generally acts like it wants to die. It won't. I never does, just ACT's like it. It will keep doing this until I "flog" it once, then it straightens out and runs perfectly. I can't just rev it, it has to be under load. Just revving it does nothing. But if I get on it in 1st, take it to 5.5K or 6K RPM and let off, it's magically fixed till I turn the car off and start it again. It will also act like it's missing while driving until the first time I do this.

Long ago it was suggested I replace the DME temp sensor. I did that a few weeks ago finally. I thought the issue was fixed. But I suspect I just hit the 15% of the time it doesn't do this. I only drove it a few times as I was in the process of a lot of work on it. Now that I've put the LR Max chips in, and have been driving it after finishing all the other work, the problem is back. Or it never left.

Any ideas? Dave Lindsey suggested I unplug the O2 sensor and see if anything changes. And inspect my injector wiring, TPS wiring, and AFM wiring. But the part that gets me, is it ALWAYS does it, just when first started, and just until I get on it once. Letting it idle doesn't seem to make any difference. I just have to get on it. It's like the old "blowing out the cobwebs" issue we used to see in the carb days.

 

Perhaps a bad soldering in a relay, sensor or the electronics?
The revving make it shake just enough to temporarly fix it.

 

I've thought about that. But once it's fixed, it stays fixed. I wondered if I had an injector that was sticking, and "getting on it" and "blowing out the cobwebs" get's it unstuck, and it will stay unstuck until it gets powered down for a few moments. Dave didn't think that was it, but I wonder.

 

Rough running issues usually first point to a vacuum leak. There can be other causes but this is most common. They are hard to trace, but there are methods using smoke, bubble solution or compressed air that are pretty effective.

If you have an aftermarket boost gauge you can also monitor vacuum that way. 16-20 in hg seems to be the normal range based on some other threads.

 

A vacuum leak or perhaps a puddle of fuel in the intake from a dripping injector that gets blown through.

 

@Dan Martinic has a good set of pictures, if you can hunt down the thread, on some cracked solder joints that were causing issues on his 951. Hopefully that's not what's affecting your car but, if so, it sounds like it's straightforward to reflow the joints.

Good luck

 

It could be worth it to look into the coolant temp sensor on the top of the block, this controls the fuel mixture on start-up, and if it is reading the wrong resistance, it might be causing it to miss or have the incorrect mixture

 

Did that a few weeks ago. What I called the DME temp sensor above. I thought it helped, but once I put in the Lindsey MAX chips it came back. Or the few times I started it between putting in the temp sensor and the new chips just landed in the 15% of the time it DOESN'T do this.

I looked over the DME and KLR for any signs of anything amiss. And Dave Lindsey, who's seen more of these boards than maybe anyone but Joe at F9 Tech, was inside it too. Not that he likely looked that hard. But it's on my radar to pull them again and hit them with a heat gun if I run out of other possibilities.

That is always my first concern, but I don't see how it could go away on it's own once I got on it the first time. I've done the full vacuum hose replacement on my 87, and the PO did this one. I've checked all I can get to just to make sure. I am planning on a smoke test at some point just to make double-sure. But I don't feel that's my current issue. I've seen what vacuum leaks act like on these. If it went away once warmed up, I'd be 100% thinking vacuum. But it does it every start, hot/cold. 2 seconds, 2 mins, 2 hours, 2 months. Every start. Vacuum is normally worse when cold.

I really keep coming back to an injector. I thought the PO had replaced them (pretty sure he said he did) but the paperwork I have shows he only replaced two. Think he got two from some place called FIVEO injectors in Washington. If it had been me, I'd have sent all 4 originals to Witchhunter and been done with it. Now I'm thinking very seriously about getting 4 new matching replacements. I'd just feel better about the whole thing then. At this point, why not? I've already dropped 4k in this pit the last month or so. What's a bit more going to matter? LMAO

 

So the running rough issue clears up when the engine is under a heaving load condition, ie high boost and high hp output. Then the engine performance is good until restarting the engine.
Is there an issue with the turbo spooling up until it senses high engine load?

 

Not per se. There is an issue with the ENGINE spooling up. It honestly feels like a miss, that just sorts itself out once it's been opened up.

On the original wires, I noticed one day while it was idling in the garage, and it was dark, I had spark jumping to the Lindsey Boost enhancer. I replaced the wires and it went away. I keep meaning to do the "in the dark" test again just to make sure my wires are not leaking again. Just keep forgetting when I'm out there.

 

@951Dreams : No affiliation, but I did just buy some injectors from them for my 928, and other folks have good experiences. These are the folks that are referenced in your documentation - https://www.fiveomotorsport.com

I think the nice part is that you can trust these guys not to stock and send the counterfeit items that people are seeing on eBay.

Good luck

 

I searched ICV (idle control valve) symptoms yesterday and found a thread in the Turbo forum of a guy describing exactly, more or less to the letter, my symptoms. He replaced the ICV, and the symptoms on a cold start went away 100%. It would die on a warm start unless he blipped the throttle, then it would straighten out. But it solved the "missing, loping, hesitating and running like a dog until driven" and almost dying on cold start issue. Mine also does NOT straighten out on a throttle blip. I have to actually start going before it settles down warm.

In a new twist, yesterday when I started my trip, it started in the garage and then promptly died. That's a first. It often ALMOST dies, but never actually dies. On instant restart, it ran perfectly, no stumbling, no low idle, and no weirdness. I'm wondering if the ICV motor just binds sometimes, but as electric motors sometimes do, frees up if blipped a few times. Like maybe it gets stuck in whatever state is its "rest" state. I might try turning the car off and back on a few times the next time I start it. See if it clears it up. I'll also do the pin bypass test at the test port. See what it does.

These are a known failure point on our 40-year-old cars. And Ian at 944online does have a replacement for $125. I might just replace it so I know for sure. I do think whatever it's doing (or not doing) the Lindsey chips like it less than the stock chips did.

I also think my idle is a bit low, just under 800. I don't think 50 RPM give or take is going to make a difference, but it can't hurt to get it right. It will also give me a chance to check all the vacuum lines and connections with the intake off.

 

IACV's can usually be removed and cleaned to restore them to working order, I would try this route first before buying one. Its hard to reach without removal of the intake manifold (I was able to fish it out on my S2 without removing but I think on the 8V cars/turbos its more difficult).

Commonly its just gunk that can be blasted out with some break cleaner. You can rig jumper wires to a 12V source to manually control the actuator making sure the actuator is working freely once cleaned. If the actuator is working properly (opening and closing the valve), then the IACV is good to go. I dont think its a motor so much as a solenoid.

And yes, if you have not checked for vacuum leaks this should be one of the first things checked.

 

The IACV was a bust. I finally got around to testing it yesterday. Bypassing makes a huge difference (worse) and I can bypass/Un bypass it while it's running and the car changes idle drastically. I really want to blame the DME temp sensor, except it's bad when warm as well. And I already replaced it. I suppose I should test it. My TPS clicks when you glance at the throttle cam sideways, so it's good as far as "clicking" goes. I suppose I should test it to make sure it's working correctly internally. Maybe remove and clean the AFM? I did a smoke test from three different points yesterday, and I have no major vacuum leaks.

I'm kinda thinking of holding off till I replace the belts/WP and get my broken exhaust manifold stud extracted and replaced. Then I'll know I've got good timing (never been sure the PO did it right, the BS's seem to be off) and I'll have the exhaust leak behind me. I was really expecting some results from the smoke test.

 

When I had issues with my temp sensor (intermittant hard to no start) it was not the sensor, it was the wires under the boot for the sensor. You need to cut or peel the boot away and check those wires, the insulation just crumbles away and they short. You can also check the signal at the dme. You could also check wiring on injectors under the boot. I ended up replacing the harness with the Lindsey ones.