I have a 86 928 which I purchased a few months ago. After correcting some front end damage and replacing the starter and intermediate gear I am beginning to work on the engine. Engine starts and idles rough(after replacing the idle stabilizer), will not develop good power from idle until at about 200rpm then seems to accelerate well for about 15 minutes(UNTIL HOT) then car accelerates well until reaching about 3500rpm and totally boggs down? I have thus far replaced dist caps and rotors, fuel filter, adjusted cam timing, replaced timing belt. Any ideas of what to go after next? Thanks for any help to a newbie.

 

How is your fuel pressure?

 

sounds stupid but check your plug wires and plugs.
start car in the dark and check if you can see the plug wires arcing back to each other and the block.

PLUG WIRES

 

Welcome to the club melad I'm sure you realize it's process of elimination but It would hurt to put a fuel pressure gage on the end of the fuel rail its fairly cheap and like Sean said its a good place to start.

Regards
Matt

 

double check the cam timing ,check the ignition firing order, #1 is on the front passenger side and #5 is front driverside of the engine.
Add a can of techron to the fuel about half a tank to a full can, lots of stop and starts are better than a long trip, this gives the chemical time to work on the injection system.
It really sounds like a vacuum leak, but the other things i have suggested will help in your search for power

 

iF i DO FIND MY FUEL PRESSURE DEGRADED WHAT COULD THE CULPRIT BE? i HAVE NOTICED A HIGH WHINNING NOISE FROM THE FUEL PUMP TODAY. CHANGED THE FUEL FILTER AND THAT HAD NO EFFECT.

 

The fuel pumps are loud on these cars. Sometimes you don't notice it until you are looking for a problem, then it sounds really loud. It is possible that the pump could be partially clogged. Take the wires off of the fuel pump and switch them around (oposite posts on fuel pump). Run the pump for a few seconds. This can dislodge any debris or gunk that gets into the pump with age. Make sure you put the wires back where you found them.

BTW, you mentioned in your first post that the car acts worse when hot. Please elaborate. If you run it until hot and then shut off, will it restart after a minute or so?

 

"until hot", scares me a bit, Tell me, is it an AT?

 

It is a manual. After I have driven for about 10 minutes is when it begins to bogg down at around 3500rpm. Eventually it will stall then it has to sit for about 15-30 minutes before it will start again? I am thinking I will check the fuel pressure and then go ahead and remove the intake to check all of the vaccum hoses, pull the valve covers to check the cam timing again, remove all of the plugs and look for fouling. Any other recommendations?

 

Check the coolant temp sensor (on the coolant bridge, with a fuel injector type connector). There are two terminals, check each to ground. When warm, each should be <1K ohms. Also the wiring tends to fall apart at the connector.

 

I'll second what PorKen said. If it's a problem that arises when the engine gets warm, check the temp sensor.

 

I would not get into taking off the valve covers I don't think your going to find anything there and I have heard that if you snap one of those bolt your going to regret it. Don't over think it , fuel presure , temp sensor, spark, start simple. Just a thought

 

Would not the Ox sensor come into play once it warms up closed loop?
Maf; also do you have one to substitute?
FP 32-lbs at Idle 39-lbs higher RPM.

 

+1 here. I was going to say that you need to verify that you haven't skipped a tooth or anything while reassembling after the TB replacement.

When he says firing order, check that the plugs go to the right locations on the distributors. It's amazing but I've read that these cars are relatively smooth even with two of the wires reversed. I'm sure it depends on which ones, but I'd verify that.

Last thing you did is probably the culprit.

 

"will not develop good power from idle until at about 200rpm then seems to accelerate well for about 15 minutes(UNTIL HOT) then car accelerates well until reaching about 3500rpm "

I would think that if it runs smooth until it's hot it isn't a jumped tooth in the timing, agian just a thought.