Engine intermitantly cuts off ??

[gedk]

My car is doing some weird stuff…

When I take the car out for a drive from cold, it runs great. Let’s say I stop at the store after the car is at operation temperature. When I get back in, it starts up fine. When I start driving, it seems fine. Then bam! At idle, the rpm’s drop to almost nothing for a split second, kind of like I turned the car off… and then, miraculously, it goes back to idle. This phenomenon also happens when driving at low speed/rpm which results in the car nose diving in a less then pleasant manner. The good news is it hasn’t happened at speed or high rpm.

Only changes I can think of is the weather is getting warmer here in NC and, last month, I switched from Bosch platinum plugs to NGK’s.

I tested the ignition, seems to be firing correctly for extended periods. I also checked the mixture and found it to be running lean- set it correctly. It definitely runs smoother now, but no change to the engine cut-out problem. Always get’s BP Amoco fuel.

Any thoughts?

For reference and to demonstrate that I baby my car, here’s how she’s set-up

It’s a ’74 911S Targa, rebuilt 15k ago. Stock CIS, Crane ignition (should have done MSD?), upgraded oil cooler, turbo valve covers, Carrera tensioners, upgraded fan, upgraded head studs, koni’s and 23/29 torsion bars and any other 2.7 things I may have forgotten. Definitely need some Fuchs and turbo tie rods… after I get this issue sorted out


Thank you.

[bigchillcar]

ged,
your '74 came with a 5-bladed fan?! anyway, my thoughts would be along the cdi box..if you don't have the oem bosch unit, often aftermarket units are responsible for strange warm temp symptoms like the one you've described..
ryan

[gedk]

Thanks... I haven't replaced it... so it's in the condition the PO left it in. Sounds like a good project for next weekend.

[mjshira]

check your grounds on the ignition system. could also be a fuel pressure problem. good luck

[Nitrometano]

Check also the coil resistance. Touch the coil at the moment the engine die. If the coil is warmer than the engine, the coil is bad. Also the ignition modules, pickup coil and cables do that problems sometimes. Check this parts.