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Toyota Rough Idle

Q. I have a 1996 Toyota 1-ton pickup with a 22RE engine with A/C and automatic transmission. I have a rough idle that shakes my column gearshift lever enough to blur the lettering on it and gently massage my backside though the seat, when in "Drive" at a stoplight, foot on brake.

Out Foxing The Fox?

Symptom has survived these efforts to eliminate it:

New rotor, wires, cap, plugs, air filter, pcv valve. A few days with timing retarded to 2.5° BTDC, then back to 5 BTDC. Addition of two small bottles inexpensive "injector cleaner," sequentially, at two gas fill ups. A few days with the "inlet port" from the EGR valve into the intake manifold blocked with a small aluminum plate, in an effort to shut down the EGR valve.

Other useful pieces of information: Truck has 156,500 miles on it. At 155,000 miles, truck had another engine installed, completely rebuilt by a conscientious local mechanic, at huge expense. I think I remember that this rough idle was happening before this "new" engine was installed.

Truck runs great outside of idle, but has had a lifelong history of pinging, improved somewhat by tweaking the timing by ear and by using hi-test gas, and has returned worse than ever since the rebuild break-in period has ended. Compression is +/- 195 psi all, using an inexpensive "hold-in" style tester. No coolant loss. A cracked head into the water jacket, with much water loss, was the impetus for the engine rebuild.

Please help if you can. No hurry. The vibration may even be improving the circulation in my thighs and buttocks.

THANK YOU!

A. A rough idle is usually indicative of a cylinder not doing it's job, and is more noticeable on a four cylinder engine. First thing I would do is set the timing back to spec. New wires, distributor cap, rotor and PCV valve eliminate an ignition problem. As far as the spark plugs go, I would recommend using NGK brand spark plugs. Over the years I have found that they work the best in a Japanese engine.

The compression looks good. When looking at compression, I really look to see that all the cylinder readings are within 5 to 10% of each other rather than a specific reading. At this point I'm going to assume that the valves are set to the proper specifications.

So we're left with fuel and air which gives us two common causes. A clogged or misfiring fuel injector or a vacuum leak. Either one will cause a lean fuel mixture and the rough idle. Let's look at each one separately.

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