Thread: My P38 is not behaving it self

Check the idle air control thingy. Don't try and move it by hand btw. it will damage it. I had to replace mine a couple of years ago and it took the damn computer months to get the auto-learning stuff up to speed so that the car would no longer stall. I also reset the adaptive learning figures in the ECU at that time.

Also an air leak in your system will wreak havoc. I tested it by using a smoke machine and a pressure hose to see where the smoke would escape. In my case it was the o-ring that closed the butterfly valve. That was a hard one to track down!

Cheers,
-P

First thing I would do is a diagnostic scan , even though the check engine light is not on, it may point you in the right direction.
My first thought is your CPS might be on the way out and causing rough running and stalling.
When they die it's a show stopper, I wouldn't drive it too far like that.
I would also check and clean the butterfly valve with carby cleaner, specially the edges, gunk can build up and cause idle problems and stalling.
Hope that is of some help.

Hi Prelude and Peter, thanks for your suggestions. I had to go out last night and it is worse when it is cold, so it may be temperature related. I have a new idle speed control valve so I will put that on tomorrow, and clean the throttle valve etc. I also have a new crankshaft position sensor in the car so I will try that as well. Once it gets up to normal operating temperature it runs quite well except for a slow idle. I will go to work on Monday and check it on a scan tool and see if there is anything abnormal.
Thanks Guys.

Hi Folks,
I have made a little progress, I replaced the idle speed control valve and wound the base idle screw out 4 turns and the idle seems a lot better. I checked for codes on the scan tool and it came up with PO131 and PO151 low voltage at the O2 sensors. I checked the fuel pressure and it was normal. But flat spots in the motor seem to be caused by a lean mixture. Increasing the fuel pressure increases idle speed and manifold vacuum. Driving the vehicle with the vacuum line disconnected from the fuel pressure regulator and the car drives a lot better. All very strange. Tomorrow I am going to go back to something my friend Tom the TAFE teacher told me. When someone brings you a vehicle with a problem, you ask 2 questions. Who was the last person to work on it and what did they do, and start looking there. So the last person to work on my vehicle was me and I changed the fuel pump. So tomorrow I am going to put the old fuel pump back in. Lucky I cut that hole in the floor. At least then I will know for sure if that new fuel pump is to blame, and if not I can move on to testing other things.
Regards,
Alan

Interesting that you found low voltage at the 02 sensors and possible lean mixture, I wonder if that might be MAF related?
I'd also check the air intake is sealed properly, unmetered air can cause problems with idle and running.
I cut a hole to do my fuel pump as well, makes life so much easier.

Hi Peter,
well I changed fuel pumps this morning and went for a short drive. Still the same. So tomorrow I will change it back. I picked up another fuel filter today, and I will change it tomorrow as well. And I will check all the intake for air leaks. And just for the hell of it I will put some Fuel injector cleaner in the tank, as all these problems started after I filled the tank. My wife's BMW was running like a bag of s--t one day, and I was very busy so I drove it to the Holden dealer and got some of their fuel system cleaner, put it in the tank and took it for a thrash on the highway. When I started it could not get up to 80 kph. On the way back it was doing about 160kph. So worth a try for the P38. I did put new injectors in it a while back so I do have a spare set.
Regards,
Alan

Hi Folks,
well I changed the fuel pump back to the new one and I then went to change the fuel filter. I wanted to see exactly what came out of the filter so I cleaned all around it and had a clean container to catch all the fuel in. So I pulled the fuel filter and drained it and it was completely clean, not a speck of dirt. I was thinking I will have to keep looking. I put the original filter back on and went to throw the fuel in the container on some weeds, and I noticed the fuel looked like it had wax floating on top of it. So I bought some Liqui Moly fuel injection cleaner. Put that in the tank and went for a drive and after a few kilometers it was running a lot better so I took it up a big steep hill near home, and it just walked up to the top. So I am hoping it is fixed but I will see how it goes tomorrow morning. If it was a load of crappy fuel I will have to change service stations and carry a couple of cans of fuel injection cleaner withe me.
Regards,
Alan

Hi Folks,
Well I drove my P38 to work today and although it was definitely better it was not perfect. So if it was the fuel it will take a while as it has over 3/4 of a tank full. I could drain the tank but I would have to grow a lot more weeds to put the old fuel on. And the missus would complain about the smell. So I think I will take it for a long drive and then refill the fuel tank and see what happens.
Regards,
Alan