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Discussion Starter #1
Hi forum,

Problem: A week ago I replaced the plugs, plug wires, coil packs, and valve cover gaskets on my 2004 IS300, and now I've got P0441 and P0446.

Observations: Of course I had to remove the throttle body and several vacuum hoses to do that job. In the process I replaced a couple of cracked, brittle hoses with non-OEM ones from Autozone. I've looked all over and don't see any hoses that I forgot to re-connect and I don't see any hoses that are pinched or anything.

I also accidentally pulled apart the fuel pressure VSV. (At least I think that's what it's called. It's the little green/grey/gold valve on the back of the throttle body, part #90910-12243.) It didn't break. The green part just came loose from the four metal clamps holding it down. I put the two pieces back together and tightened down the metal clamps. But I'm worried that I may have permanently damaged the part. Would that part failing cause P0441 and P0446?

By the way, car drives fine...no problems there. I did notice there were a few times afterward when the car didn't want to start as effortlessly as it normally does. It took a few cranks. Basically I just need to get these codes cleared before my upcoming state inspection.

Thanks in advance for any help.
 

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Yesterday was the warmest day we've had in a while (80 degrees). My car sat in the sun for several hours while I was at work. When I went to start it, it took 3 or 4 tries to get ignition. That never used to happen before I did this job. The car always started the first try. Isn't "trouble starting when warm/hot" a potential symptom of that fuel pressure VSV failing? Doesn't that valve do something to allow the car to start better when it's warm/hot?
 

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That solenoid will not cause a no start but it will cause p0441 and possibly a rough idle if stuck fully open, bring the vehicle to temp and see if it’s activating. The fact that it fell apart already is a bad indicator in my eyes.
 

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That solenoid will not cause a no start but it will cause p0441 and possibly a rough idle if stuck fully open, bring the vehicle to temp and see if it’s activating. The fact that it fell apart already is a bad indicator in my eyes.
The only way that failing would cause an issue. Would be if you got so much vacuum in the tank built up. The pump could not over come the pull back to the tank.

I have run cars without any of the system. Just a vent. With no issues other than OB2 complaining on evap. Witch is for emissions only.
 

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The only way that failing would cause an issue. Would be if you got so much vacuum in the tank built up. The pump could not over come the pull back to the tank.

I have run cars without any of the system. Just a vent. With no issues other than OB2 complaining on evap. Witch is for emissions only.
I agree with you but he’s asking what can cause the codes and failure on that solenoid will cause that code. If you’re sure the hoses are routed correctly and tight then remove the solenoid to check for continuity. You can also check it with shop air, with it closed it should not flow air to the engine side port. With it on it should.

As far as the hard start it might be your fuel pump like Solar said. Either not priming or not holding residual pressure after shut off. Best to check pressures. You don’t mention your miles but all these cars are definitely up there in age now.
 

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Discussion Starter #8
For anyone who has this same problem in the future, it turns out my instinct was correct...it appears that replacing the fuel pressure VSV solenoid on the back side of the throttle body fixed the problem. I found a used one at a junkyard for about $6, and when I bench-tested it (by connecting a 9v battery), I felt a definite difference in the amount of "click" than I had with the solenoid on my car. I replaced that part, reset the codes, and they haven't been back in several drive cycles now. Also, the difficult starting has gone away. The car cranks on the first try just like it used to before this whole thing started. I know I read somewhere (can't find the link) that if that solenoid is stuck open, it can cause difficult starting because it's allowing air into the throttle body at ignition that isn't being accounted for by the ECM, causing an imbalance. Thank you both for the help.
 
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