Qway

This is my first post on here I apologize if im not following guidelines. I have been dealing with this issue since i got my 98 gs400 last June doesnt always do it but seems to be getting worse. I have been trying my best to get info on this issue .. the car throws the common P0171 so im gonna try and check for MAF or o2 issues. While i was digging around i ran into this ... this is exactly what my car is doing ?? Any help would be greatly appreciated !!!!


Thanks for all your replies and help here. It sounds like some of you know what you're talking about. I have a 94 SC400 that has been an absolute NIGHTMARE trying to figure out the problem.

I haven't brought it into Lexus yet because they charge a fortune for every little thing and I don't trust the dealers around here after getting ripped off by them in the past. But I have brought it to my trusted mechanics who haven't been able to figure it out. If you have ANY ideas, on what I should try next it would be greatly appreciated.

Here are my symptoms-

The check engine light is usually on, but it turns off randomly and back on again at times. It was not on at all when I first bought the car, but after I brought it into the mechanic (for stalling out in a drive-through ///and it WOULD start back up but then stall out right away again. Then it started fine after sitting for a few hours. But I had it towed in anyway) Also in the MORNINGS only when it was cold, it would take a few seconds to crank/start before it started.

But if I turned the key to the drive position for 10 seconds before trying to start it, then it would start right away. I was told that meant I had a fuel pump issue) So I figured the car dying out was my fuel pump going bad so I have it towed to the shop as I said (Please bare with me here as the list of symptoms is kind of long and crazy but I need to get to the bottom of this) and the shop tells me that my fuel pump is OK, it tested fine they said under the pressure test.

But I hear these tests are not always accurate? I still suspect it could be the feul pump but I need to tell you my issues and how the car progessively is getting worse with new symptoms. Everytime I bring it into the shop they tell me I need a new part, which has not fixed the problem. First they told me I needed a Crankshaft Positiion Sensor, because they said the Computer code told them I needed it. Now they say the computer no longer tells them it needs that(to try and justify them installing it), and now it points to some kind of timing issue they say.

Well, I am 99% SURE I did NOT need that crankshaft sensor. Never had any symptoms of a bad crankshaft sensor. My car always started up everytime, it never FAILED to start, which is what happens when that sensor is bad. So I fear the computer might be giving the wrong codes. I had an idea that MAYBE my problems are tied to a bad Computer in the car? Should I try to replace the main ECU for the car?

I recently replaced the FUEL PUMP ECU, the 2nd time I brought the car in, as it DIED again, same symptoms, stalled out and it WOULD start again right away, but then die right away. I kept trying to get it to stay running and I could not. So I knew I got ripped off on that Crankshaft Posiiton Sensor, as it never fixed the problem.

Also I forgot to mention that AFTER they put that sensor in, my car had a NEW problem (which they denied causing, but it NEVER did this before I brought it to the shop) The new problem, which is really bugging me, is that when the Car is COLD, it STUTTERS AND BUCKS EXTREMELY BADLY. Infact the RPM's are hard to get over 2000 RPM. And it won't go faster than 20 MPH when it's cold. As it starts to warm up, it stop bucking so much unless I hit the gas harder, then it still does it.

So, the symptoms are COLD- I barely hit the gas and it bucks/Stutters. HOT- I can hit the gas LIGHTLY and it won't stutter and I can drive over 20 MPH. lol But this is soooo annoying that they have done this to my car. It all started after they put that CPS Sensor in (Crankshaft position sensor) which I have no idea if it's connected to that or not. I think they might of messed up some wires or created a vacuum leak or something in the process of their repair. So I bring it in again, and the 2nd time they tell me I needed a FUEL PUMP ECU and that is why my car is stalling.

So, I bought the part myself and had it (Fuel pump ECU) installed, and since then (This was only 2 weeks ago) the car has NOT stalled yet, but I fear that it will again and that they diagnosed it wrong again. Who knows. But I am more worried about this BUCKING/STUTTERING problem, as the car is basically undrivable until it gets warmed up. Even then it doesn't seem to run as good as I can never hit the gas hard to speed up or it will bog down again.

Another thing which I find strange is that my Check Engline Light was NEVER on before I brought the car in there, and it even had a SMOG cert when I bought it. I think they may have messed it up and caused the light to come on (that would mean they are dishonest though, since they told me my Light bulb was just burned out and they even charged me for a new bulb) I believe they are honest, as the reviews say they are and I never had a bad experience with them. I think they just have NO clue how to fix a Lexus.

I am leaning towards something to do with the MAF sensor (although they claimed they checked this and it was good, but it could still be the wires or something right?) I also have a REALLY BAD SMELL (Not rotton eggs) coming from the exaust. Smells like I am running rich or something. There is definitely some kind of problem(s) going on with the car and as I said before the Check engline light turned off for a BIT when they installed the Fuel Pump ECU (Also they claimed they changed the spark plug wires for me as well, since they said those were bad, but that did nothing to help this problem) And they said they checked out my Spark Plugs and those were good.

Arcadian

Here's my recent experience. Car showed CEL, shut it off, and a few hours later it would start and immediately die, again and again. Next day charged battery, started ran rough for one minute and died. Towed car to dealer. They cleared two codes, one for the engine one for the brake system (?) and the car ran fine, I picked it up, It's run fine since. In 7 years ownership (2000 GS4), it's only done this twice, once a few weeks after I bought it. Both times the weather was cool, -1 to -15C and extremely humid. Normally it's quite arid here, humidity is weird to us. So, maybe humidity in some electrical connectors, or even icing over of the MAF or throttle body.