1986 Turbo low rpm trouble

safecracker · 06-10-2004, 04:14 PM

Without boring everyone with all the details, after 5 years of owning this car and doing all of my own minor maintenance, I decided to bring it to the dealer for a 45,000 service including valve adjustment. I had some previous off and on starting trouble, but it always performed very well in the 5 years I owned it.

Here is the problem, the car now runs poorly in the idle to 3500 rpm range under load. 3500 on up, it is great as it always has been. On this recent service, they replaced both fuel pumps and the fuel pressure is no longer an issue. Is there something that this scenario would typically be the cause for the problem? I have notified the dealer after driving it the first day that it was the worst the car has ever run and it is going back to be corrected, but I am curious if this makes any sense to anyone. The mechanic is a 30 year veteran Porsche mechanic and I have been impressed with his knowledge, but I am starting to have my doubts. Any thoughts, thanks in advance. Phil

dean · 06-11-2004, 04:26 AM

It could be a bunch of things. Vacume leak, bad fuel pressures are all I can think of now. Did the mech check your fuel pumps before replacing? It doesn't sound like it was bad fuel pumps to me.

beepbeep · 06-11-2004, 04:46 AM

When I left my 930 at Porsche dealer for valve adjustment I got it back with all sorts of idle problems.

Later on, I found that couple of hoses under intercooler weren't tightened. Thing is, there is a myriad of hoses under lid of 930 and some of them (those going to throttle-bypass valve, for example) are *really* hard to get to.

Also, recirculating-valve gaskets were completly shot. I changed them and tightened all hoses and got rock-steady 900 RPM idle.

Also, higher control pressure means less fuel at idle, so you might need to re-adjust CO and idle-screw to get it up.

930 Guy · 06-11-2004, 05:45 AM

You need to determine if it's a fuel problem. If so, may be filter, accumulator, Relays, etc. If it's not fuel, sounds like a vac. leak which are hard to track. There are 3-4 connections to the intercooler and air box housing that need to be tight if they removed those items. check the rubber seal/gasket where the intercooler pipe rests down on the engine. Take the cap off your distrib. and see if it has much play both in a circle, and tip the rotor end to end. Check the cap for cracks, and that it fits down correctly, check the spark plug connections at the cap, and at the plugs. Check/set the timing at 4000 rpms with the vac line disconnected. Brian

safecracker · 06-11-2004, 02:37 PM

Thanks for your responses, originally fuel pressure was only 40 lbs and the fuel pressure is about 80 now. The car idles great, it is just when you start to go under load from idle to 3500. After that, it screams as it always has. It is going back Monday for them to fix. This was my first dealer experience in 5 years, could be my last. The car was there for 7 weeks and this is what I end up with.

ewave · 06-11-2004, 04:36 PM

I'd suspect the Warm Up Regulator. The WUR adjusts the mixture based on temperature, length of time the car has been running, manifold vacuum and boost.

gsxrken · gsxrken's Garage

Let us know what it turns out to be. Is your lambda setup intact? This may be case of your CO way off with the newly in-spec fuel pressures.