Rough idle, what am I missing here?
Jan 29, 2023 | 09:51 AM
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Rough idle, what am I missing here?
1987 22R 2WD A/T 352K miles bone stock,
I've had this truck since 70K miles, has always run & idled perfectly (as have all the 'yotas I've owned). Recently, suddenly, started to idle rough. I have done the following to rectify, so far without any luck:
Replaced carburetor (first with a new cheap chinese knock-off (piece of crap)...then rebuilt the OE carb, then finally a new Weber 32/36 DGEV...new OE mechanical fuel pump, new fuel filter...
deleted EGR system; major tune-up (plugs,cap,rotor,wires,coil,ignitor, checked the distributor pickup airgap), checked timing (0 degrees)...
Adjusted the valves, compression test shows 160 psi all cylinders. Intake manifold vacuum at 20 inches at idle, 40 at high revs...
Tried an alternate fuel supply; bypassed brake vacuum booster, smog circuits...
None of this has resolved the rough idle. It shakes annoyingly at 700 rpm, pretty hard when idling in gear (automatic). And what I really don't understand is that if I pull off #1 or #2 plug wires while idling, it dies quickly, but I can pull #3 or #4 wire off, & it has no effect whatsoever...just idles happily & roughly on 3 cylinders. My timing light insists spark is getting thru all 4 wires, right up to the plugs.
Of course, the new Weber sucks vacuum under the mounting base, but not ridiculously so.
What am I overlooking? Sure, it has 352K on it, but I've had 22R's go to 600K & still could hold a smooth idle...no matter what I do here, makes no difference at all...
I've had this truck since 70K miles, has always run & idled perfectly (as have all the 'yotas I've owned). Recently, suddenly, started to idle rough. I have done the following to rectify, so far without any luck:
Replaced carburetor (first with a new cheap chinese knock-off (piece of crap)...then rebuilt the OE carb, then finally a new Weber 32/36 DGEV...new OE mechanical fuel pump, new fuel filter...
deleted EGR system; major tune-up (plugs,cap,rotor,wires,coil,ignitor, checked the distributor pickup airgap), checked timing (0 degrees)...
Adjusted the valves, compression test shows 160 psi all cylinders. Intake manifold vacuum at 20 inches at idle, 40 at high revs...
Tried an alternate fuel supply; bypassed brake vacuum booster, smog circuits...
None of this has resolved the rough idle. It shakes annoyingly at 700 rpm, pretty hard when idling in gear (automatic). And what I really don't understand is that if I pull off #1 or #2 plug wires while idling, it dies quickly, but I can pull #3 or #4 wire off, & it has no effect whatsoever...just idles happily & roughly on 3 cylinders. My timing light insists spark is getting thru all 4 wires, right up to the plugs.
Of course, the new Weber sucks vacuum under the mounting base, but not ridiculously so.
What am I overlooking? Sure, it has 352K on it, but I've had 22R's go to 600K & still could hold a smooth idle...no matter what I do here, makes no difference at all...
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