Hey guys, I posted a while back about a 2000 GS300 that I was having a heck of a time getting up and running. Long story short, it is running again but poorly. I’m hoping someone here has some ideas of items to check because I’m at my wits end:

Symptoms:

• Slow to start when cold (have to crank for several seconds) and sometimes dies on the first attempt. Will start on the second attempt.
• Rough idle about 50% of the time.
• Severe misfiring under load. I had to drive the car over a mountain pass to get it home recently and there were a couple of times I didn’t think it would make it. Had to back almost completely off the throttle and crawl up the mountain at 25-30 until it leveled back out. CEL was on most of the drive, but flashing during two major climbs.
• Cruises great at speed in the flats as long as you stay out of the gas.
• P0300 and all of the associated mis-fire codes for the various cylinders, so it’s not just one.
• P0171 has been thrown on and off. It’s consistent lately along with the misfire codes.
• Car runs better with VVT-I OCV unplugged, obviously it throws the P01349 code if you try to rev it. Refuses to rev past 2400 RPM or so when the OCV is disabled.

Repairs completed/troubleshooting done:

• Tested compression, was all good. Within about 10 PSI on each cylinder, all near 180.
• Changed plugs, tested resistance on wires and coils, all good.
• Changed OCV.
• Changed crankshaft position sensor.
• Tested camshaft position sensor resistance, in spec.
• Changed MAF.
• Checked timing, marks are all good.
• Replaced fuel pump.
• Inspected computer, looks like it’s brand new, but who knows if there is an issue somewhere.
• Inspected all under hood wiring, looks good.
• Switched ignition coils to different spots to see if the mis-fire moved. Still a general/random code. Can’t imagine all 3 gave out intermittently and at the same time.

I’m hoping there are a couple of tests I can do to narrow down this problem. I’m supposed to be giving this car to my mother in law as she’s in need of one and I can’t get it running right. I’ve never had these kinds of issues with a Toyota product and I’ve driven a lot of them.

 

If not, replace all three ignition coil packs with new ones and the IGNITER (ignition control module) on the driver's side fender.
Also ensure that the exhaust system is not clogged. Such as clogged catalytic converters (3 pieces).
P0171 Code - Fuel Trim System Too Lean (Bank 1) - could also be a vacuum leak at the intake manifold connections (there are a multiple connections with gaskets / tubes along the way)

 

All of the plugs have spark, so I'll take another look at the ECU and keep going.

 

I pulled the ECU out. All capacitors look perfect. The only thing that looked odd was a tiny white dot on one of the chips (see attached photo). I feel good about the computer. How does one go about testing the exhaust for being clogged?

 

Have you checked for vacuum leaks? Either around the intake or the lines themselves? And how about the wires and connectors that plug into the coil packs? They're known to go bad and break apart. I had to change all of them on my 300.

Otherwise I'm wondering if it could be a fuel injector and/or regulator issue since the codes are a combination of misfiring and running too lean.

 

I have never seen or heard from anyone that the OEM injectors on Toyota / Lexus cars have failed. Even old cars with millions miles on them still work to some extent.

 

OK, so I did a couple of things and am having new weird symptoms.

• Igntion coil wire on cylinder one (from igniter) was slightly split on the insulation. I taped both parts up separately to cover the splits.
• Checked ingiter plug, all looks good, added some di-electric grease to it just to be sure.
• Switched the old OCV back in.

Now the car starts but stumbles horribly all the way down to about 200 RPM. When I give it any gas it revs lower instead of higher. Eventually it dies if I let it idle. I unpluggled the OCV, same. Put the new OCV in, same behavior. Exhaust is flowing nicely out of both pipes.

Scanned and got P1656 for OCV error, obviously because I tried to run it with it unplugged. Cleared code, same exact behavior as before. I guess vacuum leak testing is what I need to figure out next.

 

Yup. Profi do this with a smoke tester.
Search some videos online how to smoke test an intake with vacuum leaks.

 

Have you made sure the wires going to your coil packs are not deteriorating? Pull back the brittle conduit and expose the wires, i bet you find the insulation falling off.

 

I had a similar problem on my gs300. My timing had jumped, I would check your timing to make sure its in check.

 

Unless tensioner is bad how would timing jump?

 

Not sure, just what my motor did. Doesn't hurt to check.

 

I bet the problem is in his coil signal wires. You have to strip all the way to the front of the engine. Espeially the ones under the throttle body

 

I checked every vacuum hose under the hood and did a smoke test. No leaks. Airbox and resonator are both in good condition. I did get the car running enough to get it warm but it still idles way down, coughs and putters, then goes back up to 1200-1500 RPM and runs fine. I've checked the wires previously, but I'll look again. I'll also double-check the timing, but it was good last time I checked it.

 

Can you connect OBD-II diagnostic scanner and watch the throttle position sensor readings in real time?
You need to start tracking it from the beginning of the ignition ON time until it stalls.