TruckerJoe28

Hi guys, I have an '86 944 turbo with an idle problem.

I just finished a big project where I replaced:

• Timing Belt and associated rollers/pulleys
• Balance Shaft Belts and associated rollers/pulleys
• Front Engine Seals
• Vacuum Lines (including venturi delete)
• Exhaust manifold gaskets
• Flexible fuel lines to the rail
• Everything from the coil to the plugs

Now that the pieces are back together, the car won't idle, and it will only run (roughly) if I keep the throttle slightly open. I've done a fair amount of troubleshooting thus far:

• Fuel pressure in specs at rail
• Fuel flow adequate
• Pressure drop from each injector is identical using tester
• Injectors cleaned out, nothing noteworthy in spray pattern
• Strong spark in each cylinder
• Good compression in each cylinder (for a cold engine, at least)
• Triple-checked timing . . . still good
• AFM & TPS check good
• ICV/ISV cycles with 12 volts applied
• Checked for vacuum leaks

I'm out of ideas. Since it ran fine before I messed with it, and based on the troubleshooting I've done so far, I'm guessing maybe there's an issue with the vacuum plumbing. I used Lindsey Racing's vacuum diagram when I replaced the lines and removed the venturi. The only thing that wasn't explicitly clear was the configuration of the HVAC lines, but I imagine they wouldn't be consequential. Regardless, I attached the modified picture to show how I did it.

Any other components you think I ought to test? Thanks in advance for any suggestions!

PorscheFanatic202

I once replaced intake manifold gaskets and accidentally left an old gasket on one of the cylinders. I put another gasket over it. I had a slight intake leak and it ran super roughly and wouldn't idle just like you describe it... I would double check you don't have an intake vacuum leak. Put a slight pressure on the intake section and listen for air. Next I would check electrical connections once again.

NCLA951

TruckerJoe28

Thanks for the recommendation, guys. I took the intake manifold off and triple-checked all the vacuum lines, and then performed a pressure test. I didn't find anything conclusive. Just a bit of leaking from the CV, which I gather is typical.

However, now the car won't start at all. No spark. Battery is fully charged, and I cleaned all grounds. Fuel pump is operating, and I'm getting good pressure at the rail. 12 volts are getting to the injector harness with the ignition on, Noid light remains stubbornly off when cranking, no fuel smell.

Interestingly, there's also no tach bounce, but I don't suspect the speed/reference sensors. They were allowing the engine to run before I did the pressure test. Resistance checked good, but I don't have a scope to test them further. They are also relatively new and I didn't mess with them at all in the previous work.

I'm beginning to think the DME computer is faulty. Any other ideas before I go down that road?

Thanks again for the assistance.

-Joe

gpr8er

ICV they are notorious for vac leaks in the body of the valve. Big hit on the wallet.

Tom M'Guinn

Does the boost gauge jump to "1" when you turn the ignition on? If not, that's a good clue the DME/KLR may not be getting power (check the relay?). If you have no tach bounce, I'd take a look at the speed/ref sensors anyway -- peek under all 4 rubber boots for signs of frayed wires. And/or wiggle them while cranking. The sensors may be new but the harness connectors are probably 30+ years old... I hear you that they seemed to work before, but no harm in inspecting under the boots...

TruckerJoe28

gpr8er, I tested the ICV by cycling it with voltage applied to the different terminals. I heard good, positive movements from the internal valve. Didn't notice any leaking from the outside during the pressure test. Is there any way to check that further?

Tom, the boost gauge does indeed indicate pressure when I turn the ignition on. I'll mess with the sensor harness some.

Thanks, guys!

-Joe

Tom M'Guinn

If you have no fuel, no spark, and no tach bounce, then I would put all effort on that rather than ISV's, vacuum leaks, etc. If you like to play the odds, definitely check the speed/ref sensor harness. You might also open the DME and look for cracked solder joints.

Dan Martinic

If your car ran fine before your initial work, it seems these issues come from removing and replacing all that stuff. I'd say you've missed something during re-assembly each time (ex. plugging in a large vac line to the J-boot, plugging in a sensor wire, etc). There's always a lot of stuff to re-assemble. Been there, done that. It doesn't seem like you've got a bad part per se, certainly not DME or major part, assuming the car ran fine before the work

Humboldtgrin

GPA951s

- What he said and he just went through this same thing. Remember all it takes is one frayed wire to short to another on the injector harness and it will take them all down.. and the in doing all that work you obviously disturbed 30 year old brittle wires... Double check them..

Humboldtgrin

markl951

Is your DME making the ICV cycle? Easiest way to check this is to turn the ignition key on but don't start the engine. If you can feel the ICV vibrating then your DME is making it cycle. If not, then you've probably found the problem.