What do you guys think about an 86' 951 with an up and down idle? I know I have seen this problem in the past and it seems that it was something fairly simple on another 944 of mine but I can't recall what it is. The car consistently idles up and down between about 1100 rpm and 1500 rpm. The car has a new TPS sensor, but if you do unplug it the car will idle but very fast. Anyone have any ideas?

 

Is it adjusted properly? Meaning when you just open the throttle does it click?

 

I your air bypass screw completely closed???? Or open only 1 turn?

 

More than likely the throttle body is out of adjustment. In this condition the idle is too high and the DME thinks the engine is in an "Over Run" or "Trailing Throttle" state. The DME kills the injectors, RPM drops, the DME fires the injectors, RPM goes up, and the cycle repeats. The easy way to test for this is to unplug the TPS. If the cycling stops, the Throttle Body/Idle By-Pass is out of adjustment.

To set the idle, reconnect the TPS and put a jumper between pins 'B' and 'C' of the diagnostic connector and connect a Dwell/Tach to the coil. Start the engine. Use a 7mm socket to adjust the idle to 840 +- 50 RPM. Remove the jumper. Idle may rise or fall slightly, but should remain steady.

If you cannot get the mechanical idle adjusted properly, then you need to remove the throttle body so you can set the throttle plate mechanical stop.

To set the mechanical stop you need to loosen the TPS screws and the jam nut on the mechanical stop screw. Back the stop screw out until it is NOT touching the stop arm. Turn the stop screw IN until it just touches the stop arm, and then turn the stop screw IN an additional 1/2 turn. Tighten the jam nut, set the TPS, install the Throttle Body, and then set the Mechanical Idle (Diagnostics connector jumpered). Note: If the Idle By-Pass is fully closed, open the Idle By-Pass about 1 1/2 turns before you re-install the Throttle Body. This setting should get you "in the ball park."

 

Yeah the throttle clicks when you open and close it. I will have to check on the screw for its position. I feel though that it might be something more simple because the car ran fine before removing the intake manifold etc.. to replace the turbo. It seems I had a problem just like this once before and it was something simple, like something had come off or some simple mistake.

 

I know this was a longggg time ago, but.....
Did you ever resolve this issue ?
I am having a very similar problem
Thx in advance
Ed

 

I ended up rebuilding the entire engine harness and that solved the issue.

 

Yeeks !!! God help me... I hope that's not the issue
I did find that the lug nut I used, to plug the opening on the crossover CO2 test pipe fitting, just backed off and went by by, so i am praying that may have had something to do with the up and down idle
Thanks Colin
Regards
Ed
I am in the middle of hell right now ( changing out the oil pan gasket so I am seeing if I find another other leaks or potential causes )

 

I had this same problem - see here for solution: https://rennlist.com/forums/944-turb...ior-fixed.html

Summary - the ICV control circuit in the DME burns out (likely due to shorts in bad wiring in the harness to the ICV). There are two Darlington power transistors in the DME that fail. They are easy to remove and replace if you are skilled at soldering and basic electronics.

I have a pack of 25 Fairchild BDX25A transistors (http://www.fairchildsemi.com/ds/BD/BDX53C.pdf) collecting dust if anyone needs any. PM me if interested . !

 

Thanks Brad very much
What I will need to do is, again bend over and take it in the arrss
This will be the 4th time i have to dig into the DME footwell area
This car is the gift that keeps on giving
I have a crap load of stuff under the glove box, and in the glove box. that all has to come out in order to test the DME ... Thank God I have Tom here and I can probably borrow his know working DME, and if that prooves to be sucessful than I will love to buy some off ya
Thanks very much for your response
Best regards
Ed

 

I'm tempted to replace those transistors the next time I have my DME out, just as a preventative measure.... Honestly, I've seriously considered just replacing all active and logic components in the thing anyway. Maybe that will be next winter's project. Thanks Brad, for adding valuable info to the collective!

 

More than welcome to borrow a DME, but since your motor continued to surge up and down when we pulled the connector off the ISV I doubt that is why your car was acting up. I'd start by fixing the things you already found (missing lug nut, plate, etc.) and see if that does the trick before tearing more apart.

 

Thanks Tom
Yes, I didn't realize that was only affecting the ISV circuit ...
Trust me, I was not going any further with anything. until I get these other leaks taken care of .....
Balance shaft rear seal, Oil pan gasket, Cam tower, Exhaust manifold leaks etc....
This damn car has more leaks than the Titanic....
Regards
Ed
Oh I forgot, motor mounts too !!

 

My 951's casually for sale Ed if you want to start fresh... (note I didn't say new!)...

;-)

 

LOL
Aahh .... no I need my dose of more suffering, with this one, before I move on
Actually, I would really love to see a Boxster Spyder parked alongside. "Old PITA",
but until I get. "Old PITA running like it should, I wont be looking at anything...