Things already done, in order
Replaced wiring harness with new one.
Replaced MAF with good used one.
Noid checked fuel injector wires they are firing and not a constant on.
Checked temperature sensor on block ohms at temperature right on.
Checked ecu voltage at temp sensor within parameters for the temp outside.
Cleaned injector grounds.
Sprayed carb clean over entire engine looking for vacuum leaks.
Replaced Fuel Pressure Regulator

Ok To start off this car had a bad harness that was totally disintegrated and that was the start of all these problems. I cleaned the plugs up after the last try which was fuel pressure regulator. It runs but running rich it seems to be sporadic. Meaning it has a kind of lumpy idle, not chugging. like a small miss. All plugs were carbonned badly after 150mi. If I step on the gas it will accelerate rough belch black smoke and then accelerate properly. When it is cold it will pop into the airbox. I plan on picking up injectors tomorrow as well as anything else I can get my hands on. At the moment I am borrowing parts from my 940 which runs great and swapping them to the 740.
I do have a smell of gas in my 150mi oil change and that will be addressed again as I don't feel like wasting yet another oil change. Oil level is at norm but just giving all the info I can. I am at a dead loss and stumped. Is it possible that a bad O2 can make it run this poorly ? Can it have 4 bad injectors ? Is the ECU bad ?

Thanks
Bob

 

Bob: Many things to check. I once had a similar, but not exact issue with my 740T.

First: How does it idle? Start writing down how it acts cold idle, hot idle, etc so you can start to focus in on the problem.

Did you check all the vacuum fittings UNDER THE DASH? There are several above the pedals, and one of the tees let go there on me years back. Heck of a time figuring it out.

Turbo health. you didn't mention this. Is you waste-gaste functioning properly? Is the vacuum line flexing or leaking under full boost? It sounds like you are going full rich when you step on it. This is a protection mode from the ECU....indicative of a vacuum leak. Get a vacuum gauge on your turbo and give it a spin. It should be set about 7-8 lbs of max boost on your car if you have the Mistubishi turbo. Not sure about the Garrett. If you are under or way over, you have a turbo problem too.

Throttle body. Have you given this a good cleaning? A very dirty one will aggravate the motor.

Idle speed motor: Same thing. Spray it out well with carb cleaner. This is a sensitive piece. It has a wire/needle thingy inside that oscillates very fast. It gets gunked up over time. I clean mine every 2 years.

Gasoline in your oil?

ECU: THere are a lot of ECU "crossover" charts on the internet and I feel about half of them are wrong. Yours is on the right wall of the passenger footwell behind the plastic cover. Open it up, check the number on the sticker, and verify that its a match for your VIN. That alone could cause all kinds of problems. Make sure the connection is seated firm and there is no corrosion/debris in the plug. Clean it up.

I know this problem is aggravating. So sorry. But it is likely something simple like a vacuum leak that has escaped you, or another simple issue.

 

One more thing Bob....did you replace the MAF with the same number /proper model. There were several different ones on Volvos...the Turbos had the "017" and it features an adjustment screw. Also be sure that it is clean and the filaments all intact. You can get a spray can of "MAF cleaner" at any Autozone or Advance.

 

Throttle switch adjusted? Those will wreak havoc on idle quality.

 

Hmm, Vacuum under the dash I haven't checked.
The MAF I will compare Numbers tomorrow. I do still have the old one. And one on my 940t I can swap.
It has a lope on cold start. 20degrees F here. When engine warmed it idles better with just the slightest of misses. I contributed that in my mind to 264k mileage. I will also pull the Idle speed motor as well and clean it.
Throttle position I replaced and set clockwise of the click. (or top forward of the click). I had a go about it today replacing the O2 sensor as well as a "poke and hope" f.i. temperature sensor.
With new plugs oil change as well she blacked the plugs with 15min of idling. I will go over the hoses as well and look for any and all cracks.
The ecu is the correct bosch # that I did double check.
I am unsure which vacuum line you mean for the turbo ?the line from the intake manifold to the wastegate with the check valve ? Garrett or Mitsu I am unsure of.
Thanks for the response and will get on those in the morning.

Bob