3FE rough idle (1 Viewer)

[peresclay]

1991 FJ80 with 245,000mi. My issue was present before and after I recently did my injectors. When idling for a minute or 2 the engine starts to misfire, lope, and generally "run rough". A quick press on the go pedal will make the engine run correct for about 5 seconds then run poorly again after that. Smoke test shows no vacuum leaks.

Trucks has 6 cleaned, re-screened, and verified OEM injectors
New AFM
Brand new fuel filter
2 year old fuel pump(even though the age could mean nothing cause we have all seen faulty 'new parts')

 

[jonheld]

That screams "unmetered air" to me.
As the idle speed returns to 650 after a quick blip on the throttle, the A/F ratio is off. Anything above idle speed will mask this.
The entire top half of the motor should be sealed. Valve cover/grommets/oil fill cap gasket/dipstick tube gasket/side cover gasket are all good places for a leak.

 

[Marco Lau]

so rig runs fine prior to injectors cleaning?

 

[peresclay]

That screams "unmetered air" to me.
As the idle speed returns to 650 after a quick blip on the throttle, the A/F ratio is off. Anything above idle speed will mask this.
The entire top half of the motor should be sealed. Valve cover/grommets/oil fill cap gasket/dipstick tube gasket/side cover gasket are all good places for a leak.

That wouldn’t show up on the smoke test I presume?

 

[peresclay]

so rig runs fine prior to injectors cleaning?

Ran okay, injector cleaning made it peppier and took away some misfiring at low rpm’s

 

[Marco Lau]

Ran okay, injector cleaning made it peppier and took away some misfiring at low rpm’s

unmetered air is my guess if lower rpm stumble, misfiring and idling. Do you have a cracked intake boot? any vacuum hoses disconnected? If you did a smoke test to test for vacuum leaks, then you should be fine. Is your timing set correctly, valves adjusted to factory spec? Then i would look into the AFM or TPS for misalignment.

 

[peresclay]

unmetered air is my guess if lower rpm stumble, misfiring and idling. Do you have a cracked intake boot? any vacuum hoses disconnected? If you did a smoke test to test for vacuum leaks, then you should be fine. Is your timing set correctly, valves adjusted to factory spec? Then i would look into the AFM or TPS for misalignment.

Intake boot replaced, no vacuum hoses disconnected, smoke test was done at the brake booster vacuum line, the only thing I haven’t checked is the TPS…what are common symptoms of an out of alignment tps? I’ve seen it pop up now and again here on the forums

 

[kelly saad]

Same exact issue with my 89 62, exactly. Just replaced my MAF box and no luck there.