I had the same type of issue with mine and it was discovered to be several of the vacuum lines not sealing well. I'm with soontobered84, it's probably a vacuum leak somewhere.

 

If it were vacuum related, it would show up all the time, wouldn't it? His issues are related to load per his description. That's why I'm guessing it's either fuel or spark related. If the spark is ok, my next suggestion is fuel.

 

i'm going with maf problems

 

This morning she took off out of my driveway and threw me back in my seat. A very slight hesitation when it went through second gear at around 2500 RPMs, but nothing too bad. It did rocket at 3000, once it went past and shifted. But as she got warmed up near my office (10 miles), she was ******* it a little bit.

It was about 60 degrees this morning. It's been in the high 80's the other days where she's really a mess. At highway speeds she still has kick left and cruises at 70 MPH no problem.

This weekend, I'm going to try and swap out my cat and o2 sensor. I have a used cat with only 30k miles on it. Mine currently has a rattle in it anyway. I also have the replacemnt vac hoses from 928intl that I'll start to put in. I don't want to pull the entire engine apart, however, so I'll likely try to just get the ones on the outside.

Most of this started after I had my motor mounts done. It was gradual at first but got worse over the past 3 weeks.

 

Based on the last statement... I'm starting to think MAF too. One of your TwinCity bretheren should have one you can swap out easily to test.

 

One more thing that happened over the past 2 days. The car stalled 3 times while sitting at a stop light. Idle was just fine, then lights come on the dash and the engine goes out. Starts back just fine with no problem.

Only happens when sitting for about 2 minutes, but not all the time. Does that add to the riddle?

 

My WAG would be the cat. It fits all the descriptions. After warm up, under load etc.

Charley

 

We'll know in 48 hours, I guess. I noticed a lot of people with similar simptoms, but not a lot of solid conclusions. I'll be sure to report back so others don't have to sort through this issue as much as I have. So far, it's getting kind of expensive with the guessing.

 

Replacement cats were put in this morning, including a new 02 sensor. It was a nice cool day when I drove over to my friend's place to get the work done, she raced down the open road without any hesitation at all. It was only about 60 degrees out, which made her run great.

The problem is ... that was before we worked on it.

So, we swap everything out and take her out on the road and she sputters and cuts out pretty drastically. She was starving for fuel at this point. The whole process only took about 4 hours, including some other minor stuff like fixing a rattle with the torque tube (loose pinch bolt).

A few notes:

1. I used a 1 wire 02 sensor and capped the other wires
2. The problem does not happen at the high end, only in 1st and 2nd.

Our next step is to replace to fuel pressure regulator, but that's just a hunch. Anyone else want to weigh in. It almost seems like there were multiple issues happening here. The symptoms have slowly changed.

Quick question: would the fuel relay stick under acceleration, or is either open or closed?

 

you can check if your regulator is bad, ive seen a couple tricks posted on here you may want to search. But usually you can pull the vaccuum off of it and see if there is gas there. In my experience FPR rarely go bad.

 

Could you still have an issue with the fuel dampners and not the fuel press reg. I have had simmiliar issues in previous 86 and now on current 86 and was told my pressure dampners may be at fault.not the FPR...going through the same search to narrow down my own cars problems. will keep you informed on my finds.

 

I would swap the LH, EZK, and MAF. 1 at a time, take a ride. Rule out the big things. Then you have to go thru things like fuel filter, final stages, temp II sensor, even coils, and fuses and relays and grounds. A fuel pressure guage is helpful to rule out problems.

I had a sputtering and rough idle once after i put my engine back in, i had forgot to button a few things down resulting in a major air leak.

 

The 86.5 uses the first generation LH (25 pin) and an EZF spark (also only 25 pin with no "K" which denotes spark knock detection). I'd suggest first swapping MAFs. Porsche used the same MAF for all models from 1984 Euro through 1995 GTS, so it may be easier to find a "swap part" than the LH and EZF because those are only swappable between 1985 - 1986 US models. Check the vacuum line to the EZF, that provides important engine load informaton to the system.

You need to be aware of another minor technical issue - the first generation LH uses an adjustment on the MAF to set the base CO, whereas the 1987 S4 and newer 928s don't use that circuit (the lambda circuit takes control). So if the target vehicle is an older 928 and uses a MAF that has been installed on a newer 928, it may be necessary to remove the plug on the MAF that covers the adjustment access and tweak the base air/fuel adjustment. If the MAF is used from another 928 of the same generation, it also may be necessary to tweak the adjustment due to engine differences.

It isn't true that spark coils either work or don't work. They can have a heat or load related problems. So I also would suggest that you do a coil swap. You will need to find an 928 of 1985 - 1986 vintage as the coils are different in later cars.

928s use low resistance spark plug wires and the resistors are in the plug caps. This is done so that all wires have the same resistance regardless of plug wire length.

I also suggest taking the connector off the spark final drive module (located in the front, ahead of the radiator, under the plastic cap) and cleaning them up. If there is corrosion you could have intermittent problems. While you're there, remove the brown wires bolted into the chassis and make sure that those ground connections are clean.

 

Was the power issue there before you did the front brakes? If not, if the brakes are sticking at all they'll get worse as you drive and they heat up causing the car to need more engine power to overcome. Perhaps a quick check to see how hot those rotors are after you gone for a run and have the low power issue.

Just another potential symptom to eliminate.

 

What makes you think she was starving for fuel? Do you have an AFRM? One quick test that you can do is to crack the nut on the passenger fuel rail and see how much fuel is flowing. Here's the flow values.