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Need to get my 951 back on the streets

almost a year ago now, my 951 left me stranded at a stoplight. It did not stall, but the idle suddently got really rough, and car was having trouble revving. Was not drivable, had to push it into the gas station and call the tow truck. I've since left it in the garage, always putting off fixing it. My other car, camaro, recently spun a rod bearing, so i had to decide if i wanted to fix the porsche or the camaro. Porsche had that engine problem, plus needed a clutch kit... pilot bearing or TOB or something was broke. I was thinking the engine problem was due to bad vacuum lines, however i just replaced them today with the lindsey set, and it did not solve my problem. Here's some info on the car. '86 951, 45,000 - new head gasket, oil cooler gasket, FPR, dampener, vacuum hoses, ignition coil, spark plug wires, cap and rotor (i think, will check them tomorrow), tps, possibly a few other small things here and there.I think the car is running super rich or something. Bypassing ISV via jumpers did not help the idle, nor did disconnecting the o2 sensor.

Things I plan to check: make sure all 4 injectors are working, DME solder joints, AFM, speed/refernece sensors.

I know the speed and reference sensors are in the clutch housing, is it possible for transmission issues to damage them? Anyone have other suggestions? I already have the clutch kit and hardware kit, so it's too late to turn back now. Need to get the engine running properly before starting the daunting clutch job. I think the car was running a little on the hot side before it broke, had it idling for a bit to see if my fans were working properly (i don't think they were, i engaged the AC to kick them on.)

Old 06-15-2010, 10:09 PM
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I would start by measuring the fuel pressure. Maybe you have a clogged fuel filter or the fuel screen at the bottom of the tank. This would cause the car to not want to run as it's being starved for fuel. You can get a fuel pressure gauge and mount it to the fuel rail; it should reach a prescribed level (I think 35psi) and hold that pressure even after the car is turned off.
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Old 06-15-2010, 10:19 PM
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that would result in a lean situation, no? i definitely feel like it's running rich.... or on 3 cylinders or something. i'd need to buy a fuel pressure gauge to check though.
Old 06-16-2010, 12:04 AM
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It sounds like possibly the Throttle Position switch if it is having problems reving.
My 951 did the same thing. If the TPS is not working it will run but not rev.
Old 06-16-2010, 05:20 AM
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Does the tach move slighty, like up to the 200 RPM mark when you try and start? hear the starter and fuel pump? If it doesnt, the it is most likely the Speed/ Reference sensors, or the DME relais. My car used to run rich every now and then (remembering the cold months) and put in new sensors, and that rich smell soon faded away, but dont think it was the sensors that fixed the problem due to some of the other parts I put in- some the same as you.

Good site for trouble shooting- www.Clark'sGarage.com
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Old 06-16-2010, 02:19 PM
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the car will start just fine, just smokes a lot, and not in driveable condition. but it will idle, although choppy, and any attempt to rev the engine is thwarted by what feels like a clogged cat or something. however, the amount of exhaust gases coming out of the tail pipe sort of rules out cat i think.
Old 06-16-2010, 02:47 PM
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changed out the couplers and piping leading to/from the intercooler, no change.

one thing i tried though, i removed the hose that inserts on the left side of the pipe that runs from the IC to the Turbo. it runs down to under the intake... venturi hose maybe? anyhow, when i used a cork or my finger to plug the hole on the pipe, and left the line open (it's a vacuum line) the car seemed to run better. not perfect, but definitely smoother than it is now. maybe that tells us something?

upon start up, the car sounds like it's cammed or something. it smooths out a little bit, but definitely does not sound like normal.
Old 06-16-2010, 06:03 PM
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check the cat. get the car up to temp and check the temp from front to back of the cat. shouldn't be hotter at the front than it is at the back
Old 06-16-2010, 06:37 PM
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i just connected the dots in my head. i'm not sure how the ISV works, but i think i read in my other thread that if it's stuck open, then it would basically be venting vacuum to the atmosphere. so i'm assuming either the venturi lines are cracked, or the ISV is stuck, meaning when the air which goes through the hardpipe>ISV line, is eventually vented to the atmosphere instead of being in a closed circuit, as i assume it's supposed to be. in short, a big vacuum leak?

it makes more sense in my head. when i plug the hole, the air doesn't go down that pipe, meaning more air into the intake, and it starts to run right. so my problem is too much gas, but too little air.

one thing i noticed is that the car will die if i plug the hardpipe>isv line. this normal? and is the "cycling valve" the same as the ISV?
Old 06-16-2010, 06:51 PM
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Check the rubber hoses from the J boot to to the Idle Stabilization Valve and from the Idle Stabilization Valve to the intake manifold. These lines are under the intake manifold. While you are under there check all the hoses.
Good luck
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Old 06-16-2010, 06:54 PM
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Just removed the intake, took out the isv, looked clean, but sprayed it down with carb cleaner anyways. am i supposed to bend the metal tabs that keep the casing on and spray in inside as well? or just through the pipe ports?

also, to test for leaks in my tube, i was just stuffing one end and blowing through the other. they seem to be fine, however i blew through one tube a small metal thing fell out. some sort of flow reducer? a small cylindrical piece of metal with a small hole through the center. and the line is double clamped, so i assume it's supposed to be in there?

the very center pipe connecting the two metal metal tubes. see where it has a clamp in the middle?

Old 06-16-2010, 07:33 PM
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A simple bench check of the ISV is to supply 12vdc to the center pin #2 and then alternately apply ground to pin 1 then pin 3. the ISV should shuttle back and forth passing air then blocking air.
The third clamp is intended to hold the restriction in place inside the hose.
If you open the ISV I believe there is a O ring inside that you may have to replace.
good luck
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Last edited by kfray; 06-16-2010 at 08:30 PM..
Old 06-16-2010, 08:27 PM
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Have you checked the Trottle position switch?
Old 06-17-2010, 05:40 AM
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cleaned some corrosion off the DME board, car idles a lot better now. no more sputtering or anything. however, same symptoms occur when i try to give it gas.

uploading a video. when i just barely open the throttle, the car almost stalls out. and as i give it more gas, it'll rev, but not freely or quickly as it's supposed to. also, maybe i haven't heard it in a while, but something sounds different about it.



those few revs, are at maybe half throttle. it should rev all the way up with that much gas, quickly too. the last part where it dips down a lot, is with me touching the gas as lightly as possible. just barely turning the TPS. i don't get it though, ohm tested the tps as clarks-garage states, checked out fine. plus this is a new (used) one that i put in after it stopped working a year ago.

started the car again an hour later, back to idling like ****.
at "idle" the boost gauge stays about 3/4 the way to the middle... should be at .4 right?

Last edited by onspeed; 06-17-2010 at 04:35 PM..
Old 06-17-2010, 04:32 PM
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waking up early tomorrow to check the following:

DME temp sensor
injector leakage (not sure how... maybe i can disconnect one at a time and see if it runs differently from another or something)
fuel return line (read that if there's a blockage at the level sender or something, it'll cause high fuel pressure.. or dampener failed? but it was replaced just a few years ago)
connect a vacuum hose directly to FPR
reference sensor.

Old 06-17-2010, 09:07 PM
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