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Won't Run Guide

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Won't run guide.

Cranking = turning over. Because this is the won't RUN guide, we assume the car cranks fine. Even so, the battery wires should be taken off and cleaned, even if they look OK.

When the car cranks fine, but won't run, here's what you need to know!

To run, an engine needs spark, fuel, compression, and they all have to happen at the right time! It's really that simple...


Let's start at the beginning.

If you have any idling problem, you start with cleaning the Idle Air Control AKA Idle Speed Control (IAC, ISC - same thing) valve is clogged with carbon from the EGR system. If it's not clogged now, it will be in the future, and you just staved it off. It's not a question of if yours will clog. It's simply a question of when it clogs.

Remove the valve, and clean it by hand. 1mz-fe's, it's located on the underside of the throttle body, and is held on by four phillips screws. On 2vz-fe, and 3vz-fe's, it's on the firewall side of the throttle body, held on by two 12mm bolts.



2vz-fe 3vz-fe:


Next, check for vacuum leaks. Unplugged vacuum hoses, and especially cracks on the rubber hose that runs from the throttle body, to the air box.

Yes... 75% of idle problems are that easy. If it's not the Idle valve, clogged with carbon, it's probably a vacuum leak.


Check for spark. Pull a single spark plug out, grounding it well to the frame. Turning the engine over, you should have a strong white spark. Old plugs, or weak spark will be a blue color. That does not directly spell a problem. As long as it is a strong spark, with some white in the blue color, the plug is fine.

If you have a 2vz-fe, or 3vz-fe you have a distributor! Mark the distributor cap so you know it's orientation with paint, or a sharpie. They typically are held on by three screws, or three 10mm bolts. Check the rotor for small cracks - they *WILL* let moisture in. Check all of the contact points for corrosion. Check the rotor for corrosion. If any corrosion is present, you can take a small bit of emory paper (or very fine sand paper) and knock it off. If there is any suspect in the rotor, and cap, or you had to work them to get the car running - replace them. They're not $15 parts, and will go bad at some point.

While the cap is off, note the orientation of the rotor and crank the engine. If the rotor moves, your timing belt is in-tact.

1mz-fe's use coil on wire. Distributor checks are irrelevant.

Ignition timing is universally 10*btdc in all modern, wide-scale Toyota production engines. It is only adjustable on distributor equipped vehicles. If ignition timing is off for no reason on a distributor equipped engine, this can be indicative of a slipped timing belt.

Spark plug wires are NOT a typical wear item. If the car is kept inside, they regularly last 250,000 miles + before deteriorating. Simply said, if they are not grounding out, and the contacts are not damaged, they do NOT need to be replaced. Replacement wires ARE inferior... Spark plugs wires are also expensive! Ranging $90-$110usd for the v6 OEM replacement wires. Other than OEM wires, only use quality replacement wires, like Vitek, or extremely expensive ($250usd) Magnecor wires. No Auto store replacement wires!

Spark plugs are important. DO NOT use split electrode type plugs, or American brands in general. The resistance is far different that what the Nippon-Denso ignition system is designed to work on. Simply put... You will have a problem with putting Bosch plugs in most Toyota's. Normally in a short amount of time. Only use Denso, or NGK plugs.

NGK makes good generic plugs, that are very cheap (Typically on "permanent sale" in most areas for around $1-$2usd a plug). They are the OEM replacement plugs at most dealers (Surprisingly not Denso), they are not platinum, and last much longer than the 60,000 mile replacement interval. Making platinum plugs a complete waste of money.

Iridium plugs are nice, with 80,000 up to 120,000 mile life spans! Unfortunately, you would never want them in a Toyota factory engine that long. Carbon build-up will make you clean spark plugs around 60,000 miles. Which makes you ask the question... Why pay $11-$15usd a plug, for something you have to take out and clean, when you can pay $1-$2 a plug, and simply replace it.

If you have no spark at all. Check the 15amp EFI fuse (fuse box nearest battery). Check the 7.5 amp ignition fuse (same box). If still no ignition, Bridge E1 & TE1 in the Diagnostic's port (2vz-fe, and 3vz-fe) and make sure the Check engine light is flashing a stead on & off. If it is the computer is fine. The ignitor, coil/coil packs, and distributor can all be tested with a multi-meter, but go beyond this post. Ask for specific directions.


Check for fuel getting to the injectors / fuel rail! Fuel pressure at idle is normally only 30-35psig. If you are using a pressure gauge don't be shocked if you don't get at least 40psig.

Testing for fuel is laughably easy. Start by taking the gas cap off, and putting it back on. That will de-pressurize the fuel system.

If you have a cold-start injector (2vz-fe, 3vz-fe) Slowly unbolt the 12mm banjo bolt. If fuel starts draining out, you have no fuel problem.

Otherwise, pull the rubber fuel hose off the fuel rail. Gas will pour out. If gas pours out, don't test the fuel pump, don't change the fuel filter, don't check the injectors. Check for compression, or re-check ignition.

Forget the fuel filter... Like plug wires, they are NOT typical wear items in modern Japanese designed cars. They may claim 15,000-30,000 mile lives, you may hear it has a 15,000-30,000 mile. Barring the owner is a complete moron, and you pours dirt and debris in your gas. The simply fact is they all actually *need* to be replaced on a 100,000-150,000 mile cycle.

Fuel pumps are easy to check. When you supply them voltage, they turn on.

For Air-flow Meter cars (2vz-fe, 3vz-fe) The fuel pump will NOT turn on when you turn the ignition key is on. (except after an ECU reset) There is a switch in the air-flow meter that trips when the vane flap is sucked open (engine cranking). If you take your airbox apart and turn the iganition to ON, you can reach in and push the vane-flap open. Not only can you hear the fuel pump turn on. But you can hear, and feel the fuel injectors working.

1mz-fe's must apply battery voltage directly to the pump to check them.


Next check compression with a compression tester. On All modern, wide-scale Toyota production engines. Minimum compression is 142psig, maximum compression is 180psig. You want even compression across all cylinders.

If there is compression problems across all cylinders, check the timing belt, and cam orientation. The belt may have slipped, or snapped. (or the cams installed incorrectly after a re-build) Otherwise, there could be a blown head gasket (Common on Toyota v6's from the late 80's through the late 90's), or bad rings.

If compression tests OK, re-check ignition components, and check all the more in-depth parts skipped, or not tested.

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