MAF replaced (1-2-1) but still runs rough

  #1  
Old 09-29-2017, 12:03 AM
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Default MAF replaced (1-2-1) but still runs rough

Hi Folks - I'm hoping someone else has had this problem and can share:
* 1993 Volvo 940 sedan
* Check Engine and Service lights both came on, with engine running very rough and stalling out.
* Read code 1-2-1, MAF sensor. Replaced MAF and cleared codes.
* No error codes showing now, no Check Engine light, and no stalling out.
* However, symptoms persist of Service light intermittent, and is running very rough (RPM's dip by -1K or so every few seconds.

Is there something associated with the MAF that could have failed together, ie could the MAF failure have taken something else out that is still broken after MAF replacement; or, something else which could have caused MAF failure and which still persists?

Thanks!
 
  #2  
Old 09-29-2017, 04:04 AM
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RPM's dipping when you're driving is typically a sign of fuel starvation, vacuum/air leaks in the intake path, or weak/intermittent ignition.

what do the spark plugs look like?

the 'service' light comes on when you've driven 5000 miles since you reset the service button, its connected to a simple mechanical counter in the odometer. they frequently get flakey when they get old, I disconnect them unless its something easy to fix.

the CHECK ENGINE light is the one tied into the engine management
 
  #3  
Old 09-29-2017, 01:44 PM
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Does the issue persist with the MAF unplugged? (still won't run well with no MAF but is there any change/improvement)

Turn off and preferably unplug the battery before messing with the MAF (while you are at it leave the battery off for an hour or so (or however long it takes to clear the volatile memory)

Check all other things

Test ignition coil (make sure its not wet from rain or something)
check spark plugs and wires, distributor cap and rotor
Check fuel pressure (check fuel pressure regulator by disconnecting the vacuum hose and listening for any change in the engine, also smell for presence for fuel)
 
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