928s running bad

buck1 · 01-21-2006, 01:20 PM

just bought a 86 928s from a guy in new york. drove it all the way home to new orleans. car ran great except for the vibration from bad tires. put new tires on 2 days ago and she rolls fine no vibration. this morning got in started it up, ran fine for about one minute then the rpms dropped down below 700. backed it out the drive and noticed it was idling very bad. tried to drive down the street and it just wouldn't get up and go. almost like it was starving for gas or air. the car has 75000 miles on it and the k&n air filter is clean. any ideas what the problem may be?

jstobo · 01-22-2006, 06:18 PM

I would check fuel filter, fuel pump. On the right side injection fuel rail(passenger side) there is a cap that you can remove and attach a pressure gauge to check fuel pressure. There is a steel ball to seal the cap , do not loose it when you remove the cap. The spec pressure is 2.3 -2.7 bar. Good luck.

928ram · 01-23-2006, 06:06 AM

This is a maybe because I'm not sure if the '86 is the same as the S4, but there's an idle control valve that gets clogged or gummed up pretty commonly; the cure seems to be pulling the valve and cleaning with WD-40 or carb cleaner. Sorry I can't help with the location of the valve, hopefully others will chime in.

..P · 01-23-2006, 11:51 AM

The K&N issue caught my eye, and it sure wouldn't be the first MAF system a K&N ruined due to small pieces of oil getting on the wire, etc. It may be some other debris coming off the K&N filter too. I would toss the K&N, it does nothing for you except add dirt.

Please read this thread and then make up your own mind.
http://www.network54.com/Forum/426130/message/1132530270

I would check the Temp II sensor and the Thermo Time Switch, both of which are related to the cold start valve. If either goes out, it can cause hard starting and symptoms of low or no power when cold, etc.

Regards, P

jstobo · 01-23-2006, 06:05 PM

You have the LH fuel injection system. There is no cold start valve or thermotime switch. The computer makes the enrichment necessary for starting getting the temperature from the temperature sensor ll. The manual has these items to check for poor power output. Check-ground and plug connections, air flow sensor, temperature sensor ll, throttle switch, fuel injectors/injection timing, air leaks in intake, fuel pressure. Now that you have a 928 you should invest in a set of manuals. Also check or have a good mechanic check your timing belt tension and condition right away. If it goes you have a top end rebuild coming. Most critical part for preventitive maintenence in a 928 32 valve engine is the timing belt. I have just finished replacing 10 bent exhaust and 2 bent intake valves on an engine from a timing belt failure. Because your power problems were sudden, I bet you have a loose connection somewhere. Good Luck.

buck1 · 01-26-2006, 06:26 PM

thank you everyone that has replied. i will check these ideas out and post a reply when i figure it out. thanks again

buck1 · 02-09-2006, 08:48 AM

well the fuel pump is working. i changed the fuel filter. checked the fuel pressure.(well kinda) i unscrewed the cap in front of the pass. side fuel rail and when turning the motor over, fuel gushes out. i am trying to locate the idle control valve to check it. anybody know its location? still tying to locate some shop manuals. thanks