Questions and Answers
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.
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 degrees 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.
Make sure all the injectors are firing. There's two ways to check this, the easiest way is to use a mechanics stethoscope, or lacking that, a long (12" to 24"screwdriver) and place the blade at the point where the harness plugs into the injector and the other end to your ear. While the engine is running, you should hear a sharp click from each injector. If you do, that means that the injectors are working properly. Then unplug each injector in turn and see if the engine RPM's drop and the engine stumbles. If you heard the click and there is little or no change in the engine RPM, when it's unplugged, then you most likely have a clogged injector.
The fuel injector is a simple solenoid that opens and closes for a very short time. See my article on Mixing the Fuel That is why it must be kept clean. Any blockage will result in reduced fuel delivery to the cylinder. To get an idea of how small the injector opening is, take an ordinary straight pin and push it through a piece of paper. The injector opening is about half that size. So you can see how important a clean injector is. Injector cleaners that you add to the fuel are okay for maintenance, but do very little to cure a problem. The best thing to do is go to a shop that has specialized fuel injector cleaning equipment. There are some that will do it while the injectors are still in the engine and some that require their removal. After you get the injectors cleaned, you can keep using a good quality additive to help keep them clean.
I would also change the fuel filter if you have not done so. A partially clogged fuel filter will reduce the volume of fuel to the injectors.
It seems to me that your investment in an engine rebuild indicates that you plan on keeping the truck a while. If that's the case, I would consider replacing the injectors even if the cause of the rough idle is found elsewhere.
The other possibility is a vacuum leak. All air entering the engine must be measured. See my article on The Air Intake System Any unmeasured air entering the engine will cause a lean fuel mixture and will result in a rough idle. Check all the vacuum lines and hoses and make sure they are supple and have no cracks. Also make sure they are connected tightly. If the hoses are stiff or have little cracks in them, replace them. Also be sure that the lines are connected to the proper devices. There might be a Vaccum Hose Routing Diagram under the hood that will help you make sure the hoses are connected propery. As a Scottish Chief Engineer once said: "The more they overtake the plumbing, the easier it is to stop up the drain."
How can we tell if the engine is running lean? There's a simple way to check, get a can of carb cleaner with a straw attached to the nozzle. Start the engine and unplug one of the small vacuum lines on top of the intake. Stick the straw into the fitting on the manifold and squirt some of the carb cleaner into the manifold. Not a lot, just a quick squirt. If the engine smooths out and the RPM's go up. it's running lean.
Some other causes could be a bad oxygen sensor, bad Air Flow Meter and a bad Throttle position sensor. All of these should throw a code in the computer lighting up the Malfunction Indicator Light (MIL)
