fuse 11? that provides power to the in-tank fuel pump, and on a non-turbo, to the oxygen sensor ('lambda sensor') heater element.

 

Results of the Diagnostic Tests using the car's built-in LED testing unit are in.

First, I must point out a potentially significant discovery regarding the Mass Air Flow Sensor unit (MAF). When disconnected, the car runs - albeit not the greatest - and does not stall out.

Upon disconnecting wire harness, I noticed something strange. In the last of the 6 "slots" or "holes" on the harness adapter that plugs into the "teeth" of the unit, I found what appears to be a remnant of a wire. It was inside the slot and it made me further confused because I noticed this last "slot" does not contain one of those little medal insert things whatever you call them that the corresponding "tooth" on the unit plugs into. Basically, what I am saying is, There is 6 "slots" on the adapter, and 5 are normal with the medal parts inside, but one has nothing inside. There are 6 medal "teeth" on the MAF unit, so, shouldn't all the slots on the adapter have the "medal" inside? Why is one missing, is it normal?

With that said, the little copper looking piece of wire found inside the slot with the missing "medal insert" would of have to been in contact with the "tooth" corresponding to the slot. Could this have caused a short or something?

Also, I noticed the medal body part of the MAF unit was considerably hot.

All diagnostics were done correctly and all checked out good with the exception of the Engine Idle Speed Compensation for Auto Trans

It is number 3 on the Diagnostic Page toward the very bottom of that section
Engine and OBD Diagnostic Codes

 

Here are some pics to see what I was talking or typing about.

 

assuming this is a LH2.4 B230F non-turbo or b230ft turbo engine, the MAF is wired like.

1 - brown - ground
2 - blue-green - goes to ECU pin 6
3 - blue-red - goes to ECU pin 7
4 - blue-white - goes to ECU pin 8
5 - blue-yellow - goes to relay-switched ECU power
6 - yellow-white - used on B200G/B230G/B230GT only - goes to ECU pin 23.


well, we don't get B230G engines in the USA. so I guess that pin 6 is unused on US models.


if you unplug the MAF and start the car and it runs, it may indicate the MAF is bad. it runs in 'limp home' mode in this case, where there's hardly any horsepower. never plug/unplug the MAF with the car switched on, you can fry it. after testing with the MAF unplugged, the engine likely will throw a diagnostic code that will need clearing.

 

Pierce - Thank you for your ability to decipher my often complex and detailed explanations. That was exactly the type of response I was looking for.

I think I will go ahead and see what I can't get for a new MAF unit, or even a good used one.

What is your take regarding the Engine Idle Speed issue? It was the only test whose result was negative. It is supposed to flash a 1-2-4 code if functioning properly when moving the shifter from park to neutral then drive with the brake pedal depressed. It did not give a code, but continued to flash rapidly, which means it failed.

If this lack of code is telling me the EIS is faulty, what possibly could be defective? Is there a sensor or something or a series of things? I am absolutely
in the dark on this one.....

 

there's a DTM3 test that cycles the idle air valve along with other things. if you disconnect one of the hoses, attach a temporary rubber hose and blow through it, you should be able to tell if its opening/closing the airflow during that test.

the idle air valve is simply a solenoid actuated air bypass on the throttle, the ECU modulates it to maintain a constant idle speed when it senses the throttle is in the idle position by way of the idle switch on the throttle.

 

I should add that today for unknown reasons the motor seems to have lost ability to sense the depression of the accelerator pedal. The throttle still moves fine when I press the pedal, but the RPM meter stays put reflecting a constant idle no matter how aggressively I hit the pedal. Not sure if the car even will move if I try. It's like I may have just inherited an additional problem. I don't so much mind problems when they arise, its the ones that appear out of thin air that perplex me.

 

Ain't long-distance diagnostics fun!? Hell, it is difficult enough with the car right in front of someone. I had a 2002 Nissan Xterra 3.3L in my shop last week. (OBD2) with an intermittent dying at idle. (Sound familiar?) Initial oscilloscope test showed the Oxy heater voltage (13.5v or system voltage) intermittently shorting to the sensor circuit, driving that reading from an average of .3 to .6 volts (normal at idle conditions) to full system voltage. "Piece of cake!" I said to myself... and replaced the right up-stream sensor, thus curing the short to voltage problem. Problem was, the vehicle continued to die intermittently at idle. Hmmm.. MAF reading was 9 GPS and fuel trims were maxed at full negative -25%. Replaced the MAF... and all is well. These problems never flagged a DTC. Only clues were the symptoms and reading inputs of sensors to the PCM, and interpreting the PCM's response of taking away all the fuel it could as a response. (The reason it kept dying).

 

Quote:

Originally Posted by gabanja05

I should add that today for unknown reasons the motor seems to have lost ability to sense the depression of the accelerator pedal. The throttle still moves fine when I press the pedal, but the RPM meter stays put reflecting a constant idle no matter how aggressively I hit the pedal. Not sure if the car even will move if I try. It's like I may have just inherited an additional problem. I don't so much mind problems when they arise, its the ones that appear out of thin air that perplex me.

I'd give the throttle position sensor a look, also the throttle cable itself. The throttle cable broke last year on my '91 745T, and it was quite an inconvenience, since I was 45 miles from home. Uncommon, but not unheard of.

As to your original problem, I'd definitely be trying a "known good" Air Mass Meter, which is what Volvo calls the MAF. I keep a spare on hand. A part that only goes out every 20 years would be considered pretty reliable, but our cars are all 20+ years old..

 

disconnect the big air hose that goes into the throttle body, actuate the cable manually from under the hood and see if the butterfly valve inside the throttle body is moving.

also check the throttle position switch with an ohm-meter, the orange wire (pin 1) should be connected to the black wire (pin 2) which is ground when the throttle is at idle, and NOT be connected as soon as you move the throttle away from idle.

 

The MAF just arrived this morning, so I will be swapping it out this evening.

I should have mentioned long ago that the clips on the air box are broken off, and now the box does not seat properly closed as it should. When I did the tune-up, I noticed this, as I just bought the vehicle, and it was duct-taped shut. I removed all the tape and did not replace with new tape.

This could not possibly be the problem, could it? As far as the stalling?

Picture attached...

 

a loose fitting airbox means the engine could suck in unfiltered air, which means it could suck in dust, which would be bad for it long term, as dust getting into the oil would increase internal engine wear, also gum up the throttle body and idle valve even more than normal, as well as the MAF.

I'd personally probably use gaffers tape as a stop gap measure until I could find new clips (or an airbox from a junk yard). Gaffers tape is a cloth tape similar to duct tape, but with a much better synthetic adhesive that is both really sticky and peels clean. its generally matte black. its used by theater stage electricians (who are known in the trade as Gaffers).

 

Loose fitting airbox wouldn't be a problem for stalling. As pierce said, it is bad, and you _really_ should not leave it that way, but because it is before your MAF, it shouldn't make a difference in stalling. Only holes after the MAF would be problematic.

But as already mentioned, it will gum up all sorts of stuff, like your MAF that isn't great.

 

Once upon a time, Ford would threaten to void warranty on vehicles with oiled permanent air filters. They gummed up many Mass Air Flow Sensors and created havoc.

 

Due to severe weather in my region its taken me awhile to provide an update regarding my car's stalling issues.

And the winner is in, turned out to be a faulty MAF sensor. Very relieved to have found the problem, especially having only gave $39 for a used MAF meter after shipping. But unfortunately, my work on the 740 is not over yet. I am now starting to recognize issues with late shift, deferred shift, and high rpm's. Oh buddy.

I do have a check engine light and the cable to the transmission is pretty beaten up, frayed, but apparently still functioning okay.

I guess I will once again go through and look for codes again.....

 

indeed, after swapping the MAF, you should clear any codes, so the ECU will start relearning the optimal mixture.

a frayed transmission kickdown cable could certainly cause funky shifting

 

Actually, the "kickdown" moniker for the TV cable is a misnomer. The TV (throttle valve) cable provides a mechanical link to the engine so as to regulate throttle pressure against governor pressure to insure later/harder shifts at higher engine loads and earlier/softer shifts at lower engine loads. The cable being frayed is likely why you have inconsistent shift points and intermittent harshness therein. NOT replacing the cable and properly adjusting it WILL DEFINITELY result in transmission failure.

 

Excuse my continued ignorance when using the term "kickdown cable", but it is the term commonly used by those I have talked to.

Anyhow, on my cable issue...

The cable has too much slack in it, and when I pull the throttle by hand the cable does not "reset" itself once the throttle is returned to its idle position.

The cable was zip tied to the throttle when I bought the vehicle, and I accidentally pulled the cable too hard creating the mess of fray I now have.

At any rate, I am almost certain the cable is faulty (confirmed by photo images).

How does the cable detach from the transmission?

I found a guy in my town with a yard of volvo's. I tried disconnecting the cable from the transmission but it actually looks as though perhaps it has to be disconnected from inside??

I left without the cable sadly, and my 740 is sitting in the scorching sun patiently waiting for a new cable.

Also-- the car from which I attempted to remove the cable was a 1986 740 sedan non turbo 4 cylinder automatic. Will this cable even work on my 740 turbo wagon? 1991.

If it will in fact fit I am going back and getting that cable immediately....

 

The business end of the cable goes inside the transmission and hooks up to a bellcrank "cam" on the valve body, which, in turn, operates the throttle valve in the valve body. Removal requires dropping the transmission oil pan, and, in many instances, requires the removal of the valve body in order to remove the cable end from the bellcrank "cam". This is not a job for a novice, but within the scope of ability for someone capable of mid-level mechanical work. It is imperative that the work area and tools be kept immaculate. I just darted over to my on-line Shop-Key (Mitchell 1) and read the instructions for replacement of the cable, and the good news is that the valve body need not be dropped! Good luck!

 

I found a great page last night that gives several detailed accounts from folks who have experience replacing theses cables.

It sounds like just another job to me.

Between the 4 or 5 volvos I have owned in my time, and the accompanying issues they have given me, there is not much I have not tinkered with on these cars.

This is my first experience however with kickdown cables in general. The experience shall be rewarding indeed.