atb

I had a miss that was occuring around 3500rpms.

The condition has worsened to hard start, and stumbling through out the rpms range. I will intermittently get a clean pull through the rpm range, but mostly rough running.

At times, the car will settle to a fast idle, around 1100rpms, otherwise it will idle very roughly at 675rpms.

(Tom M. diagnosed a vaccuum leak, with the high idle situation becoming apparent, I think he's right.)

There are some electrical issues that have cropped up as well, and I don't know if they are related.

There's a definite short because the battery goes flat after three days of no driving, and my interior light fuse has popped.
My ARM-1 is registering only on the full lean setting, and the LED lights are not otherwise lighting up. I'm thinking this is more due to the electrical situation and not an indication that the engine is running lean. (Would a bad O2 sensor cause the poor running condition?)

I replaced the plugs, wires, caps and rotors last night, which didn't change the stumbling condition. All plugs showed a perfect burn pattern.

I remember when I first got the car, a weak battery caused a weird running situation. I just don't remember the symptoms to be this extreme.

My plan is to check for vaccuum leaks (can't hear anything from under the hood), and go through the electrical. Any pointers on testing the 02 sensor?

Thanks all, any input is greatly appreciated.

I've signed my 16 year old nephew up for a driver's skills day tomorrow, and it would suck for him to have to use his Saturn.

Tom. M

Pull out the can of propane and (as long as there are no open sparks)...and search around intake.......if it were something under the intake..I would guess either the point where the hoses go into the boot under the maf..on the passenger side..or at the base of the oil filler neck..
good luck..let me know how the troubleshooting goes..

later
Tom
89GT

sharkmeister85

Have you checked the battery out to determine its condition? It seems there might be an issue there.
Glenn

atb

Solved!- Bad MAF.

I've never seen a bad MAF react like this. Add it to the list of mystery cures for generally rough running 928's.

My car was not running rich, no black smoke, perfectly burned spark plugs.

Thanks to John Davis for the diagnosis, and the loaner MAF.

Bill Ball

Did you retry your old MAF to confirm? George Suennen had a no-start problem. We had tried a bunch of stuff. We were about to swap my MAF into his car. I unplugged his MAF. Then I plugged it right back in. His car started, ran perfectly and has done so for 3 years since (well, until he blew the motor at 189MPH). Had we just swapped in my MAF, we probably would have come to the wrong conclusion. Just to be certain.

Imo000

Bill, excellent idea.

Also did you reset the LH and EZK by disconnecting the battery for a minute? With the "new" MAF the computer needs to re-learn the new parameters.

BIMMERMIKE

Is this true only with '87 and newer? I replaced my MAF with JDS rebuilt and never thought to disconnect battery ground.

mark kibort

if you have enough juice to start the car , the battery is fine. once running, the battery can be bad, and the alternator is running the show. running volts is easy to measure, should be around 13.5v or better. battery sitting voltage near 12.5. on the Ljet models you can get the car to start as long as it is turning over. however, with the LHjet cars, it has to have a certain level of voltage under load. thats why i usually need a new mini odessy battery , as it gets week, the voltage drop gets larger and i sometimes cant get the car started, even though its turning over

mk

mark kibort

I just thought of a condition i had with the holbert car. same thing. couldnt get the car to rev up without bad misses. turned out to be a cracked ignition cap.

I also mentioned about the arcing post on the coil to the main coil wire to the cap.

vacuum leaks usually make it rough idling, but not WOT

wonder about the lean only condition. that makes no sense. unplug the sensor wire from the computer, but leave it connected to the 02 sensor. this allows you to see what the o2 sensor is doing, but the computer sees no 02 and goes full rich. (idle should be slightly higher too)

mk

atb

I'll give popping in my old MAF a shot just for kicks.

Even weirder, the ARM-1 worked perfectly again with John's MAF. I didn't disconnect the battery, she's running fine.

Imo000

Mike, as far as I know this is ture with all 32V engines, including the pre S4s. Also I think the '84-'85 Euro 16V are the same too.

John Speake

There shouldn't be a need to do a battery reset on the >MY87. But doing so could reduce the adaptation time to the new MAF.

Doing a battery reset will reset the adaptation to nominal mid range settings. This should match a new MAF pretty well, so minimum adaption is required to the LH ECU.

The 85/86 cars don't have any adaptation, so a battery rset is not appl,icable with these cars. But the idle CO and idle speed should be reset after a MAF change, as per the workshop manual.

BIMMERMIKE

I think I have the idle speed under control but 'idle CO', not a clue

John Speake

When all else fails, read the manual :-)

Vol 1 -A pages 24-204 to 24-206