fasted1953

I've been trying to locate and fix the problem that was causing me to get recurring P0171 code on my 99 GS400 (95K miles). I did all the normal, documented stuff. Each time I had to try something else.

1. MAF cleaning (fixed it for about a year)
2. MAF cleaning (didnt fix it)
3. MAF replacement (rebuilt)
4. Fix air box/resonator broken hose nipple with brass fitting (dealer broke and glued the part back on. I didnt break it off)
5. Check for vacuum leaks.
6. MAF replacement (new part from Lexus)
7. Throttle body cleaning
8. Replaced both front O2 sensors (one stripped and I had to rethread; all in all, not my idea of a fun time)

I thought the O2 sensors would fix it but I was wrong. The car was running better but the code returned. So today, I pulled the engine cover off to look for the ECT sensor, figuring that was the next thing to replace. I decided to check for vacuum leaks one more time. I sprayed soapy water on all the hose connections, looking and listening for a leak. I got to the front of the intake manifold and heard a faint hiss. I figured it was the water boiling off the hot engine. But I put my ear down and thought I heard a hiss. I could see the bubbles moving too. Got a piece of pvc pipe and used it like a stethascope. Sure enough, the hissing seemed to be coming from the PCV valve hose. I pushed it further on, and the hissing stopped. Looked at the dash, and the check engine light was out. Pulled the hose off, and sure enough, the hose was split on the bottom. Wrapped the hose with electrical tape, put it back on, and used a hose clamp to seal it better. I'll be ordering a new hose from Lexus tomorrow. I'll also be replacing my PCV valve now that I know where it is. Thinking of replacing the grommet while I'm at it. Cant be too hard to do I'm guessing.

I hope that the split hose turns out to be the real problem causing the P0171. Moral of the story, if you get a P0171 code, check really thoroughly for vacuum leaks before buying expensive parts like MAFs and sensors. A piece of hose or pipe for listening, a spray bottle and some soapy water is all you need.

Infamous 1

iTrader: (20)

Thanks for the great info

Mr Jokster

iTrader: (8)

Yup, always start with the cheap stuff first! I had some issues with MAF codes on my other car and found that where some air lines teed off for the supercharger had cracked... I actually found that on accident

fasted1953

I did check for vacuum leaks, and found a major one in the resonator box. After that I was convinced it was a sensor issue. My mechanic swore that P0171 on the GS400 was *always* a MAF. Then they thought O2 sensor, but they hesitated to charge me for the work because they werent sure. They spent a lot of time with my car hooked up to the computer, and the telemetry they showed me was very impressive. Air temp, intake air temp, O2 sensor data, fuel pressure, etc. Charged me for the diagnostic work that turned up nothing out of spec. Turns out all they needed was some soapy water.

Its amazing how much collective information there is here on this forum, and how little of it you find in action among the lexus pros.

I will probably keep my GS400 forever, partly because of the good quality of information, almost a cult following, that I find here on CL. Plus the GS400 is built like a tank, is still a very fast 4 door, and best of all... pushbutton shifters!!

Mr Jokster

iTrader: (8)

I personally wouldnt trust a mechanic whos says MAF code is ALWAYS the MAF. Many factors contribute to how a MAF works... at least he didnt charge you for all his work. And yea, we are like a cult LoL, mostly cause this car has aged 10+ years which means anything and everything that could have happened already has and hopefully has been written up. I still trip out on some of the retarded stuff that has happened to my car that I've found solutions for ha ha

fasted1953

Actually, it was the service writer who told me its almost always the MAF. These are very experienced toyota and lexus people who I trust. Unfortunately, they've gotten a bit too popular and busy for their own good (imo). Spoke with the owner today. He said it would have to be an awfully big vacuum leak to cause a P0171. He had some doubt it was the root of the problem. He also said that fixing the leak wouldnt cause the dash check engine light to go off immediately. He said the engine has to go thru a certain number of cycles, and the light would only go off on a restart. I swear it went off when I pushed the hose on further. Time will tell if it fixes the problem, right? New PCV hose should be in tomorrow.

Mr Jokster

iTrader: (8)

Damn, went off that fast? Good luck, hope it solves the problem. And hopefully this helps during future searches...

fasted1953

3 days now, and no CEL. And thats just with a hose taped back together with electrical tape. Picking up the replacement hose at Lexus today.

fasted1953

6 days now and no CEL/P0171.

Today I finally replaced the taped and clamped cracked pcv hose. While I was at it, I replaced some other hoses, fuel vapor hoses I think, clamps, pcv valve, pcv valve cover, pcv valve grommet. First time I've replaced the pcv valve in 10 years, 95K miles. Car ran noticeably smooter afterwards. One note of caution, the pcv valve grommet was hard as a rock. When I tried removing it, it started breaking up. I had to be very careful and account for all the pieces as I took it out. At one point, the bottom came off and fell into the camshaft area. Fortunately, it was easy to retrieve.

SirBev

iTrader: (1)

Okay then here's to hoping that nothing crazy happens that causes it to come back...Thanks for the info

fasted1953

Theres a few other vacuum hoses that are pretty dried out. I'm thinking of replacing them as time permits before they become issues. Next are the ones that go down to the power steering switch.

fasted1953

UPDATE: Its been 10 days now. No code. More about the issue here.

There is no substitute for a spray bottle of soapy water, patience, watching the bubbles and listening.

tom steele

how much was that hose by the way?

fasted1953

Around 15 bucks for just the PCV hose. Cheap by lexus standards. I replaced not just the PCV hose, but clamps, several fuel vapor hoses, PCV valve, PCV valve cover, PCV valve grommet. Spent about 75 bucks total. Thats on top of a handful of hoses I replaced on the other side of the engine earlier. Maybe 125 including a brass nipple and tap to fix the resonator pipe breakage. It adds up, but I've got fresh vacuum hoses almost everywhere now. After 10 years, and being able to do the replacements myself, it seemed like a good thing to do.

The Sewell web site looks like a great place to find and price parts btw. Better than getting stuck with an undermotivated clerk at the lexus parts dept.

eskay269

iTrader: (6)

I had the P0171 and P0174 codes and my mechanic replaced the MAF sensor, car feels much more responsive now.