97 lx450 Misfire below 2000 rpm, P0304 code (1 Viewer)

[basalt51]

I've read a bunch of other similar threads and clearly my first step when I can is to check my main wiring harness at the EGR, and Firewall. The main reason I am posting is I am hoping my symptoms might point to something else.

When cold, the lx450 starts and runs great for 20-30 seconds at ~1200 rpm. The misfire/rough running starts as soon as the rpms start to drop (I think when the choke goes off?). After that, it is very rough idling and any time I give it throttle up until 2000 rpm, and which point the problem is totally gone. Drop back to <2000 stumbles. Rev to 3500 and drop to above 2000 no problem. The problem seems to come and go every few seconds while it is occurring. If I pull the #4 wire the misfire is totally consistent, not so when connected.

The symptoms are the same in N, and power breaking in R, and D, though I can't get above 2000 rpm power braking. The issue also seemed to go away above 2000 rpm during little driving I have done after it started.

Headgasket has ~3000 miles on it, cap/rotor/spark plugs a little more than that.

#4 has spark. I have no idea how to get to the injector. I dropped the glove box and have no idea what I am looking at or for in there. This weekend I will pull the intake and check the wiring harness at the EGR.

What should I replace while in there?
Symptoms pointing to anything else?
The ECU in the glove box was very hot to the touch after running the motor for only 30-60 seconds. Is this a problem?

Thanks

 

[basalt51]

Can anyone explain to me what is going on when the vehicle first starts and the choke is on (higher idle) and what happens as the choke turns off?

Thanks

 

[CJF]

No codes?

 

[Cruiser Ed]

Did you wash your motor recently? I had a similar code p0303 misfire after I washed the engine and water got under the cover.

I was going to change the spark plugs anyways so I took the covers off and dried the wires and changed plugs and now it's all good.

 

[basalt51]

Nope didn't do anything under there since the head gasket.

 

[ToyotaDon]

Can anyone explain to me what is going on when the vehicle first starts and the choke is on (higher idle) and what happens as the choke turns off?

Thanks

No choke on a fuel injected engine. The ECU raises the idle to warm the engine up faster so emissions are reduced, etc. It controls the idle by opening and closing an Idle Air Control valve which bypasses the throttle plate via another passage.

If your hot ECU is related to the issue, it could be in this way: The No. 4 fuel injector could be shorted or have lower resistance than normal. The ECU turns on each fuel injector with an "injector driver". When too much current flows through the injector as the case would be if it was shorted or had low resistance, the excess current flow would cause more heat to build in the injector driver.

To check the injectors, you would first of all need at least a repair manual, preferably the EWD, to know what wires to hook up to. You would disconnect connector IL1 & ECU connector E4, then check resistance between terminal 14 of IL1 and each fuel injector terminal at the ECU (12, 11, 25, 2, 1, & 15). My recommendation is to check and compare all of them, as the FSM does not give a resistance specification for fuel injectors. If that's too confusing, just disconnect the injectors and measure them directly.

HTH

 

[jlindblom]

Agreed you should check the wiring harness near the EGR for any cracked/broken connections.

Also, have you checked all of your plug wires thoroughly (ie. swap wires from cylinder to cylinder)? I had an issue on mine where the internals of one plug wire degraded to where it would stumble on cold start, then go away as idle came up, would drive fine until it heated up and would then stumble intermittently. If I kept the revs up on the engine it would go away. It took a few days of random stumbling and poor running before it threw a misfire code on one of the cylinders.

I swapped plug wires around and the misfire followed the bad wire. Replaced all plug wires with new and the problem did not return.

Just another thought.

 

[Offroads4x4]

How many miles on it since the head gasket?
Did you clean the electrical connections and use dielectric grease when you put them back together when the head was reassembled?
Recheck your injector connections to make sure they are tight.

 

[basalt51]

Thanks for the replies

-I think the hot ECU is just due to it being 100+ here. I checked it the other day w/o having run and it was still pretty darn hot.

- I definitely swapped some plugs around. I'm not sure if I swapped the plug wires around so I'll check that also.

-head gasket was about 3-5K miles ago. I had it done so not sure what they did. I tried the checking the #4 injector connection, but it's really hard getting my hand down in there so not sure if I put enough pressure on it or not. It seems to wiggle more than I thought it should but wiggling while running doesn't make a difference.

- I started to expose the harness. What little I could get to w/o removing the air intake looks ok, though the heat wrap on it was totally charred black and crumbled right off.

I've got new spark plugs, I'm going to order new wires and cap just to eliminate that before I start removing the air intake (that looks like a pain in the a$$!), then I'll dig deeper into the harness if I still have a problem.

Thanks again. It sure runs good while warming up which is promising.

 

[basalt51]

New plugs, wires, cap, and rotor and she is purring like a kitten. I have some heat tape to wrap what part of the harness I exposed as preventative measure.

Thanks for the help!