M113 rough idle no fault codes.

[goblintinkerer]

symptoms there since owning the car. 120k miles FSH. at idle engine speed around 650rpm hot or cold there are engine vibrations often in the cabin. as if it turns into a diesel engine for a split second. it almost feels like a misfire but it isnt. checked smooth cylinder running data with obd tool and for reference value 0 to 2.5 is normal, 7.5 to 10 is a misfire. mine hovers often in 3-4 multiple cylinders sometimes goes up to 5.50. coil packs were changed as preventative maintenance, no difference. changed spark plugs to ngk IFR6D10, engine sounded a little healthier after. i tested ignition leads resistance w multimeter theyre all came ok. i connected all back with audible click. engine wiring look fine no corrosion or bad bends. pcv hoses around valve covers are intact since i changed valve cover gaskets. dont know what to check next. bad injector? how can i check them?

any suggestions welcome. thanks

 

[Petrol Pete]

When were the engine and transmission mounts last replaced ?

 

[goblintinkerer]

around 60k miles ago, im not exactly sure what year but ive it on a service sheet. second pair on the car

 

[Petrol Pete]

Have you inspected them ? oil leaking from the engine mounts and/or tear in the rubber on the transmission mount are pretty easy to check and eliminate from fault finding.

Also giving the engine a good rev while observing the engine movement is another cheap and cheerful check on mountings.

 

[G7Wagen]

Harmonic Balancer
The Crank pulley wheel is fitted on with a rubber bushing that can perish and wobble.
Common on M113 non supercharged engines

 

[goblintinkerer]

i wrote in the beginning of this post that i done an idle smooth running cylinder test through my obd scan tool and it gave rough idle numbers. engine mounts arent electrically connected theyve nothing to do with it

 

[Petrol Pete]

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About 50 minutes in

 

[alexanderfoti]

Do a smoke test on the intake system, you will probably find loads of leaks around the maf sensor/housing.

 

[goblintinkerer]

ill check injectors with that video and smoke test

 

[goblintinkerer]

Do a smoke test on the intake system, you will probably find loads of leaks around the maf sensor/housing.

i replaced both seals around MAF housing and the elbow fitting that connects to the throttle body. the seal that attaches the elbow to throttle body was cracked from age as i took it out. it made no difference after putting the new ones on. any other ideas? engine behaves the same both cold and warm, fuel economy checks out. 24mpg on dash with my style of driving. do i go pulling injectors or oxygen sensors? im honestly lost