Just when everything was going great too . Just finished a cam cover refresh, fuel lines and had injectors serviced. Ran great for about 400 miles, suddenly running very rough, idling crappy. Can't seem to find any vacuum leaks, no fuel leaks, checked plug/cap/ coil connections. All the wires, caps, plugs fairly new. Died a few times while idling when cooling fans turned off. Help?

 

Hi,

As one who has encountered similar idling issues such as yours, can you confirm how old the MAF and your Temp II sensors are on your car?

There is a check you can do on the grounds at the back of the engine too. I'm not sure how far you dove into the engine compartment to do the valve covers (perhaps maybe the intake manifold and lines were redone as well?), but there are grounds at the back of the engine under the airbox and fuel regulator/dampers. These are the LH and EZK grounds. When loose or corroded, it will cause the car to run rough as well similar to what you are experiencing.

Another test you can do to see if it is the O2 sensor failing or not is to disconnect the battery, then unplug the O2 sensor in the fuse panel under the passenger footwell. After reconnecting the battery, if the car runs better, that could be one of the culprits.

 

I will try to find these grounds and check the sensor. Just to be clear, it runs like crap under load too, not just idle.

 

When was the last time the ignition wires, plugs, caps and rotors were replaced too?

 

About 4K miles ago. I suspect the grounds, I did some research and found where those are and they are in the immediate area of the fuel hoses and where I last worked. It did smooth out when I jiggled the air filter housing around, so might be a connection. The age of temp sensor II and MAF is unknown, but I did clean the MAF using MAF spray. I need to change the temp sensor soon. I'll report back what I find. Thanks for the pointers!

 

Don there are probably only about 40 things that you need to check- keep you busy Christmas Day! Forget the 928, have fun with the family and/or get well sloshed.

Your symptoms ultimately reduce to fuel not getting through [fuel filter, in tank fuel pump pipe cracked] to name but a couple or spark [sounds unlikely unless you are having coil failures].

Have you had the MAF checked? when it fails it goes to a default limp home mode that sort of works at low revs/light loads. Just make sure it is connected correctly first. Try another known good one if someone local is kind enough to loan you a spare. Given you are in California must be a shed load on this list not too far from you. It will be interesting to see what the chaps recommend you check- I would initally start in the MAF area to eliminate that given your symptoms.

Best wishes for speedly recovery

Fred

 

MAF connector wires where it bends away from the connector in the rubber boot
CPS connector where the CPS cable joins the harness
Two grounds which you are already checking

 

Another thing I'm thinking about is if he did the valve covers, perhaps he removed the coils and their grounds. If these grounds are not secured well on the coil brackets, couldn't they lead to similar running problems as well?

 

Think I found the problem. Pulled the vacuum off of the pass side fuel regulator and gas poured out. Not good, right? I checked all the grounds/connections and they are good, sprayed deoxyit on them anyway. Car would not even start this am when cold. Roger, I'll be contacting you with a Xmas list after the holidays! Now time to go relax... let me know if I am off base with my findings. Thanks.

 

Yep, that would be a signal to replace the FPR.

 

Don,

If the FPR diaphragm has gone good chance the two dampers have or are about to let go if you do not know the history. I am not on commission from Roger [well not that I know of-?] by the way.

Regards

Fred

 

Ugh. No joy. Replaced bad dampener and temp sensor II since it was cheap and never been changed. Still runs rough, feels like running on 7 not 8. Going to check the oxygen sensor and again the area where I last worked.. injectors and fuel lines. It ran great for 3-400 miles after the work I did then this issue. Sort of stumped right now.

 

Maybe one of your fuel injectors failed. Try listening for the clicking of each one with a long screwdriver. Try disconnecting spark plug wires one at a time to see if one does not make a difference in the rough-running.

 

Check your spark plugs, they can tell you a lot on how the engine is running.

If your maf is of an unknown age, have it rebuilt. Check your wiring harness and if necessary replace parts of it that need repair.

Also check your fuel injectors with a mechanics stethoscope to see if they are running correctly, you might have a dead cylinder or your injector o-rings might be toast.

 

My '89 was running like that, ran ok but felt like it was stumbling or missing, not limp home mode.

First I tried one at a time:

- Temp II (did not fix)
- Distributer caps and rotors (did not fix)
- O2 Sensor (did not fix)
- Spark plugs (did not fix)
- MAF (did not fix)

I replaced all of the following at one shot and that seemed to solve the problem:

- all FPR's front and back of engine
- Fuel Injectors
- LH
- Fuel Lines
- Vacuum line fittings\elbows
- Vacuum check valve off brake booster

I was never able to narrow it down to one thing but my guess would be the vacuum line fittings and regulators.

Hope that helps,

Michael