Swagger93

I did my duty in searching the boards and my existing efi/951 knowledge for cause and effect, but before another round of disassembly I'd like to get some tips ...

Vehicle background: 1986 951, shimmed wastegate/Weltmeister chips/boost controlled by cycling valve and KLR/Toyota OEM dual-port recirculating valve from a 1991 MR2 Turbo (awesome!!)

The issues I have are all associated when just starting up the car for the first time in the day or perhaps after a long resting interval. It has a rough idle (engine-wide, as in not perceptible from individual cylinders, reaffirmed by individually pulling spark wires), particularly when cold.

The other symptom I'm getting involves boosting while cold. The boost just comes on in the strangest way ... Mid throttle/mid-RPM range I get a sort of hesitation, though that doesn't seem to be the word to best describe it. If I punch it (throttle position 75%-WOT) I get full boost and the usual onslaught of power. If I stay at partial throttle and wait for the revs to build I get a sudden rush of power, like a light switch just came on.

Once the car is warmed up the idle smooths out (though not as much as I'd like, using other 951s as a benchmark), and the boost problem is replaced by the usual license-losing smoothness.

I have the typical little cold start exhaust leaks, all very minor (and judging by friends cars and a year at 944 fest, a problem many live with without major consequence) and which go away completely when hot (I've also had the exhaust/x-over/WG/blah blah off many times so there are no cracks).

NEW OE motor mounts. Prolly like 400 miles on them.

Just got done realigning the woodruff key for the balance belt sprocket and the belt is definitely aligned properly(the vibration isn't even in the right range, anyhow), so that's out.

I checked the DME temp sensor impedance hot and cold, and they're fairly close to the specs found on Clark's Garage.

Pulled the TPS (it's the third motherf*ckin' one I've put on the damn car) and went as far as to open it up and give it a shot of potentiometer cleaner/lubricant. Tested it and gives a smooth range to infinity and beyond. You can still never be certain with those wily things, however.

I re-tracked the AFM several years ago as a precaution, and it hasn't many miles on it since then.

New plugs. NGK copper.

Wires are whatever the overpriced factory replacements are, Behr maybe (without looking again), about 5 years old and were replaced by PO. Not much more than 2k miles since then, and no perceptible arcing in the dark.

Car did it before and after Weltmeister chips, but I don't know about the shims. The thing ran so poorly and was driven so little for the first few years of ownership during college that these problems didn't show up until after I had fixed all the other issues. I made the shims myself like four years ago, and while I'm certain I measured them with a micrometer, perhaps that has some bearing with less valve travel (kinda out there). I know the thing's a junk design from the get-go but it's not boost taper that's the issue.

FINALLY: the distributor cap/rotor. Yes, it is somewhat worn. I cleaned it up with a dremel wire brush and some methanol, and it made no difference. I know this seems obvious, but honestly I've owned 10 or so turbocharged cars and NONE has ever been as sensitive (or sensitive at all, for that matter) to worn/dirty distributor contacts as people allege they are on Rennlist.

I saw one post that indicated similar issues with the cap/rotor could potentially at issue, though the symptoms were marginally unique. I'm just averse to buying an $80 cap/rotor combo every 20k or less.

Any other ideas?

Tom M'Guinn

Have you checked the vacuum and/or pressure tested for leaks?

Swagger93

Ya, it's sealed and tested with all new lines, clamps and gaskets.