Ok, here we go. my 1991 volvo 240 wagon has the following problem. i can start the engine in three to four turns of the starter. It will idel normal. no hesitation, no noise, no smoke. the problem is in the acceleration, when hitting the pedal ther is no direct reaction. Whit 3 seconds the rpm's will go up slightly, then it will bog down to idle.

I have replaced the following. new idle air control, new in tank fuel pump, new throttle position sensor, swapped fuel regulator on fuel rail, new fuel filter.
when unplugging the spark plugs and injectors one at a time, engine idles rough. meaning all spark plugs and injectors are hitting. when unhooking the hose from the idle control valve to the hose going ionto the throttle body, engine dies. when unplugging the MAF, engine dies, When unplugging the knock sensor engine dies. when unhooking the air intake pipe you hear the engine suck in all the air, and dies.
this indecates to me the MAF, knock sensor, idle air control all work correct.

I am puzzled by this. it is acting like it is not getting fuel / injectors not speeding up with RPM.
could this be a bad computer????

 

i'd be more inclined to think bad MAF.

 

thanks for your answer. I do not have a MAF i can swap. how do i test one to see if it is bad?

 

I don't know any way to test them other than swapping, the hot wire signal is quite low level.


silly question, presumably this car has thrown no OBD-1 codes ?

 

not that i can find out. i have put the pin in number 2 and 3, the only once that are hooked up, but not sure how to pull codes.

 

s/b be jumper 2 for EFI and 6 for ignition.

see Engine and OBD Diagnostic Codes
(LH3.1 is pretty much the same as 2.4)

 

Thanks. Will try when i get home. I already put the jumper in and pushed the button, no flashing. But will try again.

 

its ignition off, insert jumper into #2, key on (but not start), press button for over 1 second but not over 3, then release, and it should then slowly blink out a code. 1-1-1 is no errors. if there's any other code, press the button another 1-3 secs, see if there's another code, when the first code repeats you've got them all. key off, move jumper to #6, and repeat.

 

on my wait to test.

Thanks!!

 

oof, just looked it up, the LH3.1 cars use a unique MAF, -001, so you can't swap for any 89+ 240/740/940, only with another LH3.1 90-92 240 (and AFAIK, only some 90-92's were LH3.1)

 

Got new maf in. No difference. Could a bad o2sensor do this? Perhaps it is reading not enough air thus not allowing more fuel?

 

a bad O2 sensor would be throwing ECU faults via the onboard diagnostics.

 

Could it be a bad ecm? I am lost with this one.

 

its quite conceivable the new MAF is bad too, depending on where you got it from and who rebuilt it, especially if this was a cheap no-name rebuilder.

but its also possible there's wiring problems, and maybe even an ECU problem.

at this point, I think I'd be inclined to dig out the ECU (its just forward of the passenger door hinge, behind the plastic kick panel to the right of the passenger footwell), and unplug it, and take meter readings of the various sensor circuits connected to it. verify that the idle switch circuit opens when the gas pedal is depressed sligthly, verify the resistance of the engine coolant temp sensor is in range, etc etc.